Pests

Introduction

Buildings provide warm, sheltered, and occasionally moist environment for a variety of living organisms. In addition, the building, or its contents or occupants may also provide a supply of food. Such organisms can cause damage to buildings or inconvenience to building occupants. Pest organisms range from spiders to sycamore trees, from feral cats to fungi, and from the greater spotted woodpecker to the more infamous lesser spotted lead nicker. In most cases, exclusion and environmental control are preferred methods of dealing with the problem. Occasionally, more drastic measures may need to be taken, but legal restrictions should be borne in mind, and also the need to protect the health of the building occupants.

Building pests

Arachnids

Mites
Window-sill mite
Flour mite
Cheese mite
Furniture mite
Furniture mite
House dust mites
Itch mite
Straw itch mite
Clover mite
Predator mite
Other arachnids
Spiders
False scorpions
Scorpions
Ticks

 

Insects: miscellaneous

Ants Bees
Honey bees
Mining bees
Wasps
Social wasps
Solitary wasps
Woodwasps
Horntails
Ichneumon wasp
Earwigs
European earwig
Cockroaches
German cockroach
Oriental cockroach
Cockroach control
Termites
Natural history of termites
European termites
Damage caused by termites
Prevention of damage by termites
Eradication of termites
Beetles
Weevils
Euophyryum confine
Euophyryum rufum
Pentarthrum huttoni
Oak longhorn beetle
Bark beetle
Ptilinus pectinicornis
Spider beetles
Ptinus tectus
Ptinus fur
Deathwatch beetle
Steely blue beetle
House longhorn beetle
(see also timber decay)
For common furniture beetle (woodworm) go to timber decay
Woodworm (separate article)
Flies
Mosquitoes
Aquatic larvae
Culicine mosquitoes
Anopheline mosquitoes
Control of mosquitoes
Eliminate breeding sites
Insecticides
Physical destruction

Other flies

Hover flies
House flies
Face fly
Cluster fly
Lesser house fly
Bluebottles
Greenbottles

Bugs
Bedbug
Natural history
Control
Butterflies and Moths
White shouldered house moth
Brown house moth
Common clothes moth
Case-bearing clothes moth
Tapestry moth
Fleas
Human flea
Dog flea
Cat flea
Tropical or oriental flea
Other invertebrate pests
Woodlice
Slugs and snails
Tapeworms, flukes and roundworms

Birds and buildings

Type of buildings

  • Type of buildings
  • ‘modern’ buildings with curtain walls
  • ‘traditional’ styles
  • ledges
  • cornices; parapets
  • sills
  • bridges

Purpose of building

  • purpose of building
  • locality
  • construction and ease of cleaning

Effect of droppings

  • on materials
  • on appearance; on paved areas
  • on health; physical effects
  • nests and carcases
  • directly caused damage
  • maintenance

Birds: miscellaneous species

Pigeons: (see also timber decay)

Natural history of the pigeon

  • Behaviour
  • Food
  • Breeding
  • Survival in towns

Problems caused by pigeons

  • Health and safety issues
  • Diseases spread by pigeons
  • Pigeon faeces problems

Pigeon control

Investigation of pigeon problems

  • Site investigation
  • Analysis of data
  • Remedial programme
  • Specialised control and exclusion techniques;
  • Damage control measures
  • Routine inspection and cleaning
  • Food reduction
  • Management measures
  • Overview

Mammalian pests

Exclusion of mammalian pests

Species

Natural history of rodents

  • Brown rat
  • Black rat
  • House mouse
  • Field mouse
  • Rodent control
  • Identifying a rodent problem
  • Tooth marks and gnawing
  • Faecal droppings; Urine droplets
  • Grease marks and dirt
  • Nests of shredded material; Paw prints
  • Burrows or holes
  • Sounds of gnawing, squeaking, or scampering
  • Odour
  • Live or dead rodents observed
  • Capabilities of rats
  • Capabilities of mice
  • Additional exclusion methods
  • Metal cladding
  • Prevention of climbing
  • Poisoning and trapping
  • Rat baits and poisons
  • Mouse baits and poisons
  • Traps
  • Anticoagulant poisons
  • Acute poisons
  • Antidotes to poisons
  • Fumigation

Plant growth and buildings

Plants, building users and building owners

  • structural considerations
  • plant growth over boundaries;
  • poisonous plants
  • plants and planning
  • other restrictions

Climbing plants

  • Climbing plants and moisture
  • root damage and climbing plants
  • above ground physical damage from climbing plants
  • general recommendations
  • types of climbing plants

Weeds

Mosses and lichens

Fungi and bacteria

Trees


Insects: miscellaneous

Beetles

Weevils

Weevil infestations are a consequence of fungal infection and like fungal infections they are eradicated by drying out and ventilation. However, weevil infestation increases the structural damage caused by the fungus. Where it is expected that the wood will remain damp, it may be protected by a suitable fungicide-insecticide treatment

Euophyryum confine

Euophyryum rufum

Euophyryum rufum is similar to Euophyryum confine and is also a native of New Zealand. It is widely distributed throughout Britain

Pentarthrum huttoni

Pentarthrum huttoni is an indigenous species and widespread in Britain and Ireland. Brownish to pitch black in colour it is 3 to 5mm long. Attacking damp, partially decayed timber (usually involving Coniophora cerebella), the larvae burrow for about six months in the wood, before pupating. The flight holes are ragged and irregular and are inclined at 45 degrees to the surface of the wood.

Oak longhorn beetle, Phymatodes testaceus

This beetle lives entirely on bark and is harmless. It lays its eggs only under the bark of newly felled oak, chestnut or other hardwood. If this bark is not completely removed the wood is used in building, oval flight holes are produced, resembling those of the House Longhorn beetle.

Bark beetle, Ernobius mollis

The bark beetle, 3 to 6mm long and light yellowish brown in colour, is sometimes mistaken for the Death-watch beetle. Originating in northern Europe, the beetle is now distributed worldwide. The larvae tunnel in the sapwood of newly felled coniferous timber, being found up to 50mm from the bark, and consequently end up in timber used for building purposes. After pupating, the adult beetle tunnels to the surface, making a flight hole 2mm in diameter. Building timber is not re-infected and apart from correct identification no action needs to be taken in response to the adult beetle’s emergence.

Ptilinus pectinicornis

Common throughout Europe and the middle east, this insect is not much seen in Britain. It is reddish in colour and about 3mm long, and like the woodworm beetle, it causes damage to dry wood. An infestation resembles that caused by the Woodworm beetle.

Spider beetles, Ptinus spp

Voracious and omnivorous, these beetles have long spindly legs and a constriction in the thorax, giving them a superficial resemblance to spiders.

Ptinus tectus

Ptinus tectus is said to have originated in Tasmania, but has now spread worldwide, particularly in the colder regions. Unable to survive above 28 degrees celcius, it remains active down to 2 degrees. 3.5 to 4mm long, the beetle is a dull reddish colour. The larvae eat almost any type of dry, stored food, as well as carpets and furs. In dwellings, the beetles live on food and other organic debris, frequently hiding between floorcoards, and sometimes emerging in large numbers. Mainly confined to towns.

Ptinus fur

Ptinus fur is an indigenous species found mainly in the rotting bark of old broad leaved trees. 3 to 4.5mm long and rusty brown, it will eat almost any organic matter of vegetable origin – stored food, paper, old fabrics, cork, decayed wood, sawdust or woodshaving. Infestation often starts in birds’ nests in and around buildings.

Deathwatch beetle, Xestobium rufovillosum

Reddish brown, 8 to 10 mm long, with patches of short stiff yellow hairs. Often has dust from emergence hole sticking to it, obscuring red-brown colour. Infestation indicated by perfectly circular flight holes and by circular bun shaped pellets of wood dust. Adult stage lives less than six weeks, larvae remain in wood for 3 to 10 years. Outside the sapwood, the beetle only attacks wood which has been previously decayed by the fungus Coniophora cerebella. In Winchester Cathedral, an infestation followed after damp-related decay by another fungus, Phellinus megaloporus.

Steely blue beetle, Korynetes caeruleus

Bright steely blue beetle, predator of the deathwatch beetle, and slightly smaller. Indicates the presence of deathwatch infestations, and may also be used for biological control.

longhorn
lhbhole2House longhorn beetle, Hylotrupes bajalus

Adults
black or dull brown beetle, 10-20mm long, grey patches of hair on wing covers, smooth central line with shiny bumps either side. Emerges from infected timber from July to October.

Larvae
up to 30mm long, straight, pale cream, three small black dots on either side of mouth.

Found in sapwood of most softwood. Infestations mostly in area around Surrey and SW London, where the Building Regulations stipulate treatment of timber intended to prevent the further spread of the insect.
Infestations may be recognised by oval, 6mm to 10mm oval, often ragged emergence holes. The bore dust consists of gritty-feeling cream, sausage shaped pellets. Larval activity may occasionally be audible as a scraping sound. Badly infected timber should be removed and burned.

Note: Details of all suspected outbreaks of House longhorn beetle should be reported to the Building Research Establishment’s Timber and Protection Division, Princes Risborough, Bucks, where records are maintained of all infestations in Britain.

Flies

Mosquitoes

There are two groups of mosquitoes, culcicine and anopheline, the larval stages of both are spent in stagnant water. At best, these insects are a serious nuisance, and several species are vectors for a number of diseases

With climatic warming, increasing frequency of overseas travel, and decreasing effectiveness of both anti-malarial drugs and insecticides, the importance of eliminating breeding sites for mosquitoes cannot be over-stressed.

Aquatic larvae

The larval stages of mosquitoes develop in stagnant water and live by filtering micro-organisms living in the water. Any temporary ponding may be used for breeding; bottles, cans, gutters, rainwater butts, old tyres etc. Removal of water containing rubbish can greatly reduce the numbers of urban mosquitoes. Covering the surface of necessary still water such as water butts inhibits egg laying and removing light inhibits micro-organism growth and hence reduces larval growth. Eggs, once laid, can remain dormant for months if the water dries up. Mosquito larvae, when disturbed, move in a characteristic jerking, curling movement.

Culicine mosquitoes

Culicine mosquitoes are represented in Britain by Culex pipiens and Theobaldia annulata. Culex pipiens commonly seeks shelter in buildings, but rarely attacks humans. Theobaldia is one of the largest mosquitoes and has a particularly painful bite which often becomes inflamed. Mosquitoes of this group do not appear to transmit disease in Britain, but in the tropics they are vectors for yellow fever, dengue fever and filariasis. The adults rest with their abdomens parallel to the wall and the larvae hang down from the water surface.

Anopheline mosquitoes

Anopheline mosquitoes, represented in Britain by Anopheles maculipennis are vectors for malaria. Malaria is rare in Britain and is mainly seen in people recently arrived from overseas, but was endemic in East Anglia and elsewhere until the 17th century. Adults in this group rest with their abdomens pointing away from the wall. Larvae at rest in water lie with their bodies parallel to the surface.

Control of mosquitoes

There are three approaches to mosquito control; removal of breeding sites, destruction of larvae, destruction of adults, and deterring the insects from biting.

Eliminate breeding sites

Mosquitos have a range of several kilometres, and have an extremely sensitive sense of smell. While the individual householder may have little control over land use over the surronding area, every bit helps. Eliminate open stagnant water, or at least prevent aerial access to it. Examples include ponding in gutters, water cisterns, stagnant streams, bogs and drains. Rainwater collecting in discarded tyres is said to be one of the commonest breeding sites in South Africa.

Where stagnant water can neither be covered nor drained, stocking with predators such as fish should be considered. However, it should be noted that fish may be affected by insecticides, particularly the pyrethroids. As a last resort, pouring oil onto the water surface is said to block the larval breathing tube, and prevent them from adhering to the water surface.

Insecticides

Destruction of larvae by insecticides is not recommended as relatively large amounts of insecticide are needed to obtain a lethal concentration. This not only causes pollution, it tends to encourage the development of resistant strains. However, adult mosquitoes frequently enter buildings, either in search of victims, or in order to shelter, and fumigation or insecticide sprays may then be useful.

Physical destruction

Mosquitoes at night are strongly attracted to short wavelength light, green to ultra-violet. They are also attracted by butyric acid, reportedly the smell of smelly feet. Insects so attracted may be destroyed by electrocution, a rapidly spinning blade, by sticky fly papers, or even by insecticide.

Other flies

Hover flies

Harmless or beneficial insects, often disguised to look like wasps or bumble bees. The black, bee-like Eristalis tenax, lays its eggs in stagnant water containing rotting animal or vegetable matter, eg in drains, gutters and sewage disposal pits. The eggs hatch into ‘rat tail maggots’ which suspend themselves from the water surface by means of a breathing tube attached to the posterior part of the abdomen.

House flies, Musca domestica

Associated the world over with human habitation, the house fly creates great annoyance and some threat to health. The adults, because they feed on a wide range of food ranging from sugar to dung, are passive vectors of pathogens. The larvae develop in decaying foodstuffs, preferably in warm places up to a temperature of 50 degrees celsius. The larvae, when fully fed, burrow in soil for up to 50m to find a cool dry place to pupate.

Face fly, Musca autumnalis

Cattle pest which feeds on secretions from the eyes, nose and mouth of cattle, as well as any sweat or blood from wounds or scratches. The larvae develop in animal dung. The adults can be a pest in buildings when they hibernate in large numbers in roof voids, walls and other spaces.

Cluster fly, Pollenia rudis

Recognisable by the furry golden hair on its thorax, the adult cluster fly is in itself completely harmless. The larvae are parasites of earthworms. However, in rural and semi-rural areas, the flies enter buildings and building spaces in huge numbers at night, and in the autumn to hibernate. When the flies wake in response to warmer conditions, they can cause considerable annoyance, and by falling into unprotected tanks they can foul the water supply.

Lesser house fly, Fannia canicularis

Similar to the common house fly, but smaller, this fly is very common throughout Europe. Its larvae develop in animal dung. It has not been shown to spread any particular disease, but its habits are similar to those of the common house fly, and it must therefore be regarded as a health hazard. A peculiarity of the species is that the males fly backwards and forwards in short, jerky movements eg around a light fitting. They can keep this up for hours

Bluebottles, Calliphora vomitoria

Bluebottles, recognisable by their large size (8 to 14mm), bluish tinge and bristly bodies, only enter buildings in order to lay their eggs on meat. Their maggots may appear after migrating from roof spaces etc, where they may have been feeding on the carcases of pigeons, rats or other vermin

Greenbottles, Lucilia spp

Like the bluebottle, these flies, only enter buildings in search of animal matter on which to lay their eggs. Greenbottle larvae have been found in unhealed wounds both in humans and livestock.

Bugs

Bedbug, Cimex lectularius

Originating in the middle east, the bedbug is now found around the world. The adult is about 6mm long, leaf like, its colour varying from amber to red or mahogany colour. There are no wings, but the legs are well developed. The larval stages are smaller and more translucent versions of the adult.

Natural history

Bedbugs in the daytime hide in cracks in buildings and furniture and emerge at night time to find a human or animal host. They puncture the skin and drink up to four times their own volume of blood. When alarmed they emit a noxious odour, which combined with the smell of an unhygienic bedroom is particularly nauseating. The bugs leave characteristic speckled brown or black deposits of faecal matter around their hiding places

Control

Bedbugs and their eggs are killed by very high or low temperatures – 2 hours at -17 degrees celsius or 1 hour at 45 degress celsius. Eggs and immature bugs die off after 30 to 60 days below 9 degrees celsius, but adults are not much affected, although largely dormant. Insecticides, eg pyrethroids are effective against bedbugs, provided that it can reach the crevices where the insects hide. Ants, spiders, false scorpions and assasin bugs are enthusiastic predators of bedbugs. Bedbugs are not known to spread disease, but a minority of people are very sensitive to their bites

Other bugs

Bat bugs, poultry bugs and swallow bugs may be introduced into buildings as a result of the roosting or nesting activity of their hosts. These bugs occasionally bite humans.

Butterflies and Moths

Butterflies do not damage buildings, but it must be borne in mind that some species which hibernate in buildings are protected under the Wildlife and Countryside Act. The larvae of several species of moth may damage building contents. Wood in contact with infested material may be damaged by shallow boring or scoring

White shouldered house moth, Endrosis sarcitrella

Scavenger feeding on grain or vegetable debris in dwellings, farm buildings, warehouses. Wingspan 12-22mm, wings grey with dark patches and white ‘shoulders’

Brown house moth, Hofmannophila pseudospretella

Scavenger feeding on grain or other vegetable debris, but requiring damp conditions for development. May occur in large numbers in warehouses, but also in houses where it may damage clothes, furnishings and cork floor inlays. Bird’s nests are a frequent route of entry of the moth larvae into buildings. Wingspan 15-22mm, bronze brown with dark brown or black flecks in the fore wings

When the ambient conditions become less humid, the larvae are not destroyed. Instead they enter a dormant phase, and can stay like this for weeks until suitable conditions arise again. This moth is one of the most destructive of the house moths. Able to eat a wide variety of animal and plant material, it wreaks havoc, particularly in museums. Furs, skins, insect collections, seeds, dried fruit, carpets, herbs, clothing, leather and bookbindings can all be destroyed in a remarkably short period of times. Museums are notoriously short of money for capital expenditure and repairs and may as a consequence be damp and unheated. Neglect, damp conditions and storage that is not moth-proof have often led to the loss of irreplaceable material

Common clothes moth, Tineola bisselliella

Pest of wool in warehouses and dwellings. Wingspan 12-17mm, golden buff to yellowish grey. Very agile, but the female only flies when disturbed. Eggs 1mm diameter, white found attached to wool or fur. Larval faecal pellets, 1mm diameter and not attached to materials are sometimes mistaken for eggs. The larvae usually spin tubes of silk in which they live

Infestations may be counteracted by washing, dry cleaning, ironing or airing woollen clothes before storing them in sealed units, and using proprietary anti-moth compounds. Clean clothes are much less likely to be attacked than worn clothes

Case-bearing clothes moth, Tineapellionella

Pest of wool, hair, feather pillows and stored dried food or vegetable drugs. Dusky brown with three, (sometimes feint) spots on the forewing. Wingspan 12-17mm. The larvae makes a case of silk (and any available cloth fibre) which it drags with it as it moves around. The case is 6 to 9mm long and the larva dies if separated from the case

Tapestry moth, Trichophaga tapetzella

Mottled black and white, wingspan less than 12mm, only rarely found in dwellings.

Fleas

Small wingless insects, yellow to almost black in colour, with a hard narrow body covered in backward pointing spines. About 1000 species are known
all are in their adult stages are external parasites on mammals and birds, and feed on their blood. They are attracted by warmth, avoid light, and are intensely sensitive to vibrations. Most species have eyes, except those that parasitise nocturnal or subterranean species

The eggs are white or cream coloured, and unlike those of most other external parasites, do not adhere to the host, but instead fall to the ground, where the larvae feed on debris and faecal matter. The larvae are whitish, very active, worm-like and up to 4mm in length. When fully developed, the larva spins a cocoon to which stick fine dust particles, thus concealing it. The length of time pupating varies, but hatching may be triggered by vibration, for example, that caused by a person walking across the floor of a deserted house

Flea infestations are not related to building defects, but the nature and contents of buildings and building finishes can affect the ease with which infestations can be eradicated. When rats and mice are eliminated from building, their fleas can often, out of hunger, attack Man. It is therefore prudent to follow rodent eradication procedures with insecticidal sprays such as pyrethrins

Fleas are responsible for the transmission of a number of diseases, most notably plague and typhus

Human flea, Pulex irritans

Occurs throughout the world. Main host is Man but domestic animals such as dogs and cats also attacked, and with some wild animals such as foxes, badgers and hedgehogs. It is also particularly well adapted for living on pigs, and can occur in great abundance in pig sties

The human flea can transmit the plague bacterium, Pasteurella pestis, between individual humans, but it is not responsible for the major outbreaks

Dog flea, Ctenocephalides canis

Cosmopolitan, parasitises cats, rabbits and Man as well as dogs. The flea larva may act as the vector for the dog tapeworm

Cat flea, Ctenocephalides felis

Affects mainly cats, but other animals, including Man affected. May cause serious skin inflammation in victims who become sensitised to its saliva. Acts as a vector of plague in Africa

Tropical or oriental flea, Xenopsylla cheopsis

The most effective vector of plague, this flea is mainly tropical in distribution and is only rarely found in Britain.

Other invertebrate pests

Invertebrates other than the arthropoda cause little damage to buildings, although some may pose a health risk to occupants

Woodlice

Woodlice are crustaceans. They have little ability to prevent water loss from their bodies, so they must of necessity frequent damp places, where they feed on fungi and decaying vegetable matter. They do no harm to sound materials, but the dark faecal matter can cause spoiling

Slugs and snails

These are rarely found in buildings, except in areas of extreme and persistant damp. One species of snail, has been observed to gouge tracks on the surface of calcareous surfaces, such as lime plaster

Tapeworms, flukes and roundworms

These are agents of disease for both Man and his animals. They are often spread as a result of faecal contamination or contaminated water supply. The the risk of their spreading should be taken into account in the design of buildings and building services, particularly in areas where they are endemic.

Birds and buildings

Birds, on account of their being able to gain access at all levels of a building, and on account of their propensity to carry around nesting material and other debris can indirectly cause both structural and environmental health problems in buildings. More infrequently, birds in their search for food, nesting materials or roosting or nesting sites, can also directly cause actual damage to the fabric of a building. Birds may also cause serious inconvenience to building occupants as a result of noise, aggressive behaviour and fouling

Type of buildings

Building type more than anything determines the degree of nuisance posed by birds

Birds: Miscellaneous species

Gulls

There are three main species of gull: Larus argentatus, the herring gull, Larus fuscus, the lesser black headed gull and Rissa tridactyla, the Kittiwake

Since about 1940, gulls have increasingly taken to occupying buildings for both nesting and perching. Their numbers have been increasing throughout most of this century, although a recent decline has been reported. Nests on houses are usually on the roof, often between the chimney pots. Nests have also been reported on the flat roofs and even window sills of warehouses. Apart from the soiling of the building fabric by excrement, fouling and blockage of gutters, during the breeding season, the birds tend to attack anyone approaching the nesting sites thus rendering maintenance impossible. The birds also cause noise nuisance, particularly in the early morning

Sparrows

Passer domesticus, the house sparrow, is widely distributed and lives in close association with human activities. Damage is caused by the transport of nesting materials which can block spouts, gutters and downpipes, pose a fire risk and cause fouling of tanks and cisterns

Tits

Tits have been reported to peck away putty on freshly glazed windows. They have also been reported to cause minor damage to interior finishes and building contents

Starlings

Starlings are middle sized, sociable, aggressive birds recognisable by their jerky walk and iridescent plumage. Although rarely seen far from human habitation, starlings were not noted in towns prior to 1900. Problems arise both from nesting and communal roosting. The nests are large, untidy masses of feathers and vegetable matter fitted into any suitable aperture such as hopperheads, gutters, downpipes and roof or wall spaces if a bird sized hole exists. Apart from the effect on drainage, the nests become particularly insanitary as the chicks hatch. The communal roosting habit of starlings also creates problems. Since the same roosts may be used for months at a time, large amounts of faeces may build up, and the noise, from late afternoon until well after nightfall, may be intolerable

Control may be achieved by spasmodic scaring of the roosting birds, preventing access or even using repellent chemicals

Woodpeckers

There are two British species of woodpecker, the Greater Spotted and the Lesser Spotted. Both are protected under the Wildlife and Countryside Act.

Woodpeckers cause occasional damage to the exterior woodwork of buildings. The most common is drumming, which male birds indulge in to define territories and as part of the courtship ritual. Targets are chosen for their resonant characteristics rather than their insect content, and include shingles, cladding, eaves and even aerial masts and downpipes. The behaviour may be deterred by painting the surface with 10 per cent pentachlorophenol oil (this may cause staining), by suspending strips of aluminium foil over the surface, or by shielding with chicken wire or nylon netting

Occasional damage to insect infested timbers has been reported. The wooden churches of Romania, sadly neglected during the Communist era, have recently suffered severe damage from woodpeckers in search of wood boring insects.

Pigeons

The feral pigeon Columba livia var. and its by-products are very familiar to those involved in building surveying and maintenance
especially to those working in city centres

Many pest control companies offer pigeon control services and many pigeon exclusion systems are marketed. However there is a general lack of understanding of the problem among management and building professionals. This means that the control techniques used are often inappropriate or misapplied with the result that they are ineffective. This is not an insignificant problem as tens or even hundreds of thousands of pounds can be spent on pigeon related contracts without proper independent advice or specification and without proper competitive tendering. Such ‘one off’ measures applying a single technique with no reference to other factors are often doomed to failure. This is because pigeons are living organisms and are able to adapt over time and space to circumvent most measures

As with other biologically based building problems their control requires the application of a continuing strategy of measures to control the combination of environmental factors which favour their activities. This requires some background knowledge and the careful assessment of each case

Natural history of the pigeon

The feral pigeon Columba livia var. is descended from the wild rock dove which inhabits both inland and sea cliffs around the mediterranean and along the west coast of Europe [1]. This species was domesticated by the ancient Egyptians and has spread all over the world in many different domestic strains. The feral pigeon stocks are derived from many different strains of escaped ornamental, racing and domestic stocks but tend to revert to a wild type of colouring and conformation

These birds are well-adapted to survive in a modern city environment where the tall buildings provide habitats very similar to the cliff homes of their ancestors.

Behaviour

In all activities that do not involve reproduction, the pigeon is a social bird which will actively seek the company of others in order to rest, preen, and feed. They may therefore form flocks of anything from tens to hundreds of individuals, depending on the available food sources. These flocks develop a set pattern of activity, based around a defined set of feeding, resting and roosting sites. However, birds disturbed from one roosting area may choose another, and continue there just as if they had never been disturbed.

Food

The natural diet of pigeons is one of seeds and grains but they easily learn to exploit a large range of processed vegetable and animal products. In addition to which, they also require a source of a grit for their crops, and a source of water

Breeding

Given an adequate food supply the pigeon can breed throughout the year and a stable pair bond is formed. Preferred nesting sites are dark enclosed areas simulating a cave or a crevice [3]. Two eggs are usually produced, and hatch within 17 to 22 days. Incubation is shared. The young reach maturity in about 4 weeks. When newly hatched, the young are very immature, being blind and without feathers. For the first few days, they are fed with ‘pigeons’ milk’, a cheesy substance produced in the wall of the crop. Three broods may be produced by a pair each breeding season and individuals may live as long as thirty years

Survival in towns

The most important factor in pigeon survival is the active promotion of their population by man, for recreational and emotional reasons. This is most significant in the provision of food, and in giving protection from human predation. The uncontrolled increase in populations of feral pigeons resulting from this commensal relationship has produced considerable problems in many city and seaport environments. These can be reduced by appropriate management and public education programmes

Problems caused by pigeons

Pigeon activity in and around a building may directly damage the structure as pigeons are capable of lifting roof coverings to force an entry, especially if these are already slightly displaced. This activity can allow significant water penetration into the building and subsequent decay. More seriously, they block rainwater drainage systems with their faeces, feathers and other detritus. This can cause massive water penetration and severe decay problems. Nesting activity is particularly dangerous in this respect as pigeons frequently nest in hopperheads and parapet gutters causing complete blockage in a very short time. This disruption of drainage and the resultant water penetration is especially damaging in unoccupied buildings where problems are less likely to be detected before major damage has been done. The results of water penetration are also more serious as there may already be serious damp and decay problems in the buildings. Pigeon activity of this sort can thus negate the effect of conservation and remedial work. This represents a considerable waste of time and money, and may lead to the degradation and loss of valuable building features

Pigeon detritus and especially pigeon faeces represents both an aesthetic and a public health problem. This is particularly so when pigeons obtain access to the interior of a building. Pigeon droppings quickly deface finishes both to the inside and outside of buildings and are difficult and expensive to remove

Health and safety issues

If measures are not taken to minimise pigeon activity around a building, their presence will cause significant problems for building management and maintenance. These problems are both avoidable and expensive to deal with. They can also have an appreciable effect on the cost of renovation works and the time taken to complete a project

Though they are actively fed and encouraged by many members of the public, pigeons represent a public nuisance as well as a health hazard. This may be because of disturbance caused by calling or nesting activity in the early hours, by spreading of fleas and other parasites into inhabited buildings and by pestering for food. However, the most resented nuisance is caused by faeces. This is a potential problem where arches or ledges projected over public areas. Further problems might be expected if the pigeons are allowed to occupy scaffolding to be erected around a building

Diseases spread by pigeons

The presence of feral pigeons and most especially their faeces represents a potential health hazard to employees and to the general public. This is particularly so when large accumulations of filth build up inside a building

They are commonly carriers of a number of serious human diseases including salmonellosis, psiticosis and pseudo-tuberculosis. Their faeces provide an ideal environment for the growth of the organisms causing such diseases as histoplasmosis, aspergillosis, cryptococcis and listeriosis. Although the risk of infection from pigeons may be relatively low, the diseases are severe and may be life threatening

Pigeon faeces
problems

Health and safety problems are also caused by the build up of faeces due to the slippery and unsafe footing it provides on walkways and ledges endearing proper maintenance. This may also be a particular problem during building works and renovation

Pigeon faeces represent a health and safety hazard for employees who have to remove them or work in their vicinity. They are thus a special problem in the renovation of buildings where large accumulations have been allowed to build up. Dealing with such accumulations can be expensive and time consuming because of the protective equipment and procedures that may be required

Pigeon control:
reducing bird populations

Many techniques have been used for controlling pigeons around buildings all of which have advantages and disadvantages [4]. Some of the more common techniques currently employed are listed below when considering control options it is useful to distinguish those that reduce pigeon numbers in an area or merely modify their behaviour

Food reduction

This is the most successful long-term measure for controlling absolute numbers of pigeons in an area. During the Second World War reduction of food availability dramatically reduced the numbers of pigeons despite the increase in suitable nesting and roosting sites

Poisons and narcotic baits

Poisons can provide an effective control especially those producing a period of deranged behaviour. This alarms other birds in the flock and they will avoid the location in the future. Narcotic baits are available which stupify the birds which may then be collected and disposed of by licensed bird handlers. Poisoning of birds is illegal in the UK

Trapping

Pigeons may be caught in live traps after a short period of baiting. A large proportion of a flock feeding in a given area can be removed by this technique. Traps require a private area for operation and regular attention by an experienced operator. The problem of this technique and others that involve the removal of birds from an area without reducing the suitability of the environment is that other birds will soon move in from adjacent areas.

Birth control and removal of nest sites

Baits impregnated with birth control agents can be used but have limited uses as decreases in reproduction are made up by increased recruitment of birds from other areas. Removal of nest sites reduces reproduction but more importantly obliges breeding birds to leave the area. Nesting activity is a major source of the detritus blocking drainage around the building.

Shooting

Shooting using an air gun or .22 garden gun may not significantly affect pigeon population. However, it is an effective method of scaring the birds away from a location. If carried out regularly at the time birds are settling for the night it will prevent a roost being established at that location.

Predators

Food supplies rather than predators are the main determinants of pigeon numbers. However, falcons and other raptors are used successfully to clear birds from feeding sites such as airfields. In buildings the problem often arises from roosting rather than feeding behaviour. When threatened by a raptor, pigeons tend to cower into their roosts rather than fly away. Therefore the use of trained airborne predators would not be useful in these circumstances, but around airfields, the aim of control methods is to reduce the risk of aircraft bird strikes, rather than to prevent roosting. Domesticated carnivores such as mink, ferrets or cats will kill individual birds. More significantly they will disturb the birds in those areas where they hunt, preventing roosting, resting and nesting.

Reducing pigeon occupancy

In general, methods of reducing pigeon populations available to the owner of an individual building in an urban area are unlikely to be effective, and even less likely to be acceptable

Bird scarers

Bird scarers may be visual, audio, mechanical or a combination [2]. They work by producing a stimulus that is perceived as frightening or noxious by the pigeons. Unfortunately they have proved generally ineffective for this species due to its great adaptability and learning powers. Unless reinforced by actual pigeon deaths, they soon learn to ignore alarming sights and sounds. Appropriate reinforcement may involve killing pigeons and displaying their carcasses

The use of recorded alarm calls is also ineffective in this species, primarily because no true alarm call has been identified but also because when alarmed the rock pigeon tends to sit tight on its perch. The use of noxious stimuli such as loud sirens or explosions often becomes ineffective for similar reasons. These techniques are also unacceptable around occupied buildings due to the disturbance and nuisance they cause to people

Bird nets

Fine, standard large mesh plastic nets are used to exclude pigeons from areas of a building. They may be used in large sections to wall off whole areas or in small strips to prevent pigeon access to individual features. Fixing should be by stainless steel pins and wires. Colour is generally black to reduce decay of the plastic by ultra violet sunlight

Netting is a very effective and economical way of preventing pigeon damage on a building, but may have the following problems
netting may give a hazy appearance to buildings with finely detailed decoration and it may be obtrusive on light or brightly coloured buildings. The use of netting in small sections requires relatively high numbers of fixing points and it has a life of five to ten years

The heaviest gauge netting possible should be used and special attention paid to reinforcing it at edges or attachment points. If this is not done it will soon tear loose. In large areas and in exposed locations the net should be reinforced with stainless steel wire

Sprung wires

Stainless steel wire may be mounted on thin stainless steel brackets via short springs of the same material. These are placed a few inches above ledges at an appropriate height to interfere with landing and take-off by the pigeons. This is especially useful on narrow ledges and very cost effective where long straight runs of a few metres can be laid. Such wiring is unobtrusive, is easily removed and replaced for maintenance work, and has a life of at least ten years

Spikes

Several different systems of stainless steel or plastic spikes are available for fitting to buildings to discourage pigeons from landing. Although some of these are quite effective they suffer from a number of problems
sharp steel spikes are very dangerous to maintenance personnel, litter may become caught on the spikes, build-up of faeces makes them ineffective, their appearance may be unattractive, they are relatively expensive and they may require more fixing points than nets or wires

Repellent gels

A number of adhesive gels are available which are intended to be spread on surfaces so as to make it unpleasant for the birds to perch. These can be effective when fresh. However they are expensive and loose their effect after a year or so. This means they require regular replacement and are uneconomical in most cases. The gels can also cause damage or fouling problems themselves and can be very difficult to clean off a building once applied. They may be unaesthetic and hazardous for those working on the treated surfaces

Investigation of pigeon problems

The control of pigeons and pigeon related problems requires the coordinated application of a combination of measures and attention to detail. Application of single techniques is at best inefficient and is often ineffective. What is required therefore is a careful assessment of the pigeon problem, the ecological factors favouring the pigeons and those factors that could be most cost effectively controlled. This necessitates a site investigation and some analysis

Site investigation

A specialist investigation should be carried out to determine the activity of the feral pigeons at the building. This investigation should define the extent of the problem. Often the most significant problems are not immediately obvious and those which may be causing most management disquiet may in reality be trivial. The short and long term consequence of the problem should be assessed and costed so that their relative importance is appreciated The next stage is to carry out a detailed study of the ecology of the pigeon population in the area. This should include mapping of pigeon numbers and activity around the building through a 24 hour period, assessing critical factors such as feeding sites, roosting sites, nesting sites and loafing areas The factors limiting pigeon population in the area should be assessed. The most important of these factors is usually the availability of food sources. The proportion of sick and out of condition birds in the population and the general condition of the birds should be determined. The effect of current and previous pigeon control measures should be noted. It is important to identify which of the pigeons activities are causing the identified problems, for example, nesting activity causing blocked drains, or roosting causing faecal contamination

Analysis of data

The results of the investigation of pigeon ecology around the problems building should be analysed in detail. Using the data it is possible to determine which pigeon activities and environmental factors are significant in causing the problems identified. Simple statistical techniques and graphic representation of the can be especially useful for this purpose. They are also very useful in demonstrating the problems to the property owner or manager. The next step is to identify the factors limiting the pigeon population, and those limiting the troublesome activities. For example the availability of safe nest sites may be the critical factor attracting activity around a particular building. Alternatively the availability of sheltered roosting sites may be crucial It is essential to identify factors which can be controlled in a cost-effective manner. Required works and/or management measures can then be identified

Remedial programme

A comprehensive remedial programme should be developed using the results of the investigation and analysis. This must take into account the management and use of the building as well as aesthetic and financial constraints Only rarely will it be possible to eliminate a pigeon population or to totally exclude pigeons from a building. In most cases a percentage reduction in pigeon numbers or the control of a particularly damaging activity is all that is required. Appreciation of this fact, and the presentation of achievable targets to the building owner or manager will prevent disappointment The early definition of acceptable limits to pigeon activity will also prevent the over-use of particular techniques where the law of diminishing returns can result in wasted resources and defaced buildings

Specialised control and exclusion techniques

A combination of specialist techniques should be chosen taking into account their costs and limitations Care and attention to detail in specification and application are essential, or even the most suitable techniques or product will be inefficient or ineffective. For example, the positioning of wires can be critical and a single faulty attachment point in a net system can make it useless The side effects of each protection technique on other aspects of the performance of the building must be carefully dealt with. For example, nets or spikes may trap rubbish, fixing points may allow water ingress or accelerated erosion of surfaces, and most products will restrict access by maintenance personnel

Blocking up of internal cavities, for example roof spaces, without due regard to the provision of suitable ventilation, may result in condensation and damp related decay problems

Damage control measures

It is often cost effective to take steps to limit the damaging effects of pigeon activity and this can often be easier than controlling the pigeons themselves. To this end hopperheads and secret gutters draining the roof surfaces should be cleared of all pigeon detritus. They should then be protected from future blockage with ‘sausages’ of crushed chicken wire or secured with mesh grills. In either case provision should be made for clearing any debris that accumulates. The provision of adequate access facilities and safety points for clearing pigeon affected areas is also important

Routine inspection and cleaning

The building should be routinely inspected for pigeons, fresh faeces, nesting materials and pigeon related problems such as blocked roof drainage systems. The building should also be checked for building defects that could allow pigeon access to the interior of the roof spaces. Any detritus should be cleaned off the structure and any defects should be repaired as necessary. Such a programme would require a minimum of monthly inspection. Again provision of adequate access and equipment is very important.

Food reduction

A continuous and vigorous policy of food restriction should be applied around the building. This should involve the elimination of refuse and litter by regular cleaning, the use of pigeon-proof refuse containers, and public education to discourage voluntary feeding. This is the most important measure in any pest control strategy.

Management measures

Responsibility for aspects of the control of the pigeon problem must be specifically included in the programmes for the management of the cleaning and maintenance of the building. This will require appropriate budget provisions to be made.

Overall responsibility for pigeon management should be given to an individual manager and relevant accounts kept so that the cost of pigeon damage and its prevention can be assessed. In addition the overall pigeon problem in the area should be assessed annually as part of the building management programme in order to assess the efficiency of the programme.

Usually such a programme would be the responsibility of those managers responsible for cleaning, but there may be advantages in making pigeon control a Health and Safety responsibility in order to increase its priority.

Overview

The control of feral pigeons is a management problem which requires the continuous application of a number of measures over a period of time. Control is therefore unlikely to be achieved by the application of a single product or technique. The most important measures to be taken are often general maintenance and management works. This is especially true as total elimination of the pigeons and their associated problems is unlikely to be cost effective or even achievable.

Efficient pigeon control requires that the extent and nature of the problem should be defined before any action is contemplated. Goals should then be set that are acceptable and achievable within the resources available. It is then important to monitor the effect of any measures taken and to take further actions as necessary.

As in all building remedial work the key factors are independent investigation and advice, careful specification, competitive tendering, a holistic approach, and continued monitoring [5]

Mammalian pests

Effective pest control programs emphasize preventative measures. The first and best defence against mammalian pests is to exclude them from the building. Until exclusion methods are in place or if exclusion proves impossible, continuous trapping may be necessary. After trapping has been effectively carried out, exclusion techniques should be maintained to prevent more pests from entering the building.

Resort to chemical control methods only when trapping methods have failed. Contact poisons, poison baiting, and fumigation result in animals dying in inaccessible locations where their corpses will putrefy and attract insect pests. Poisons will not prevent recurrence of the pest problem unless exclusion methods are thoroughly carried out.

Because many recommended pesticides are, to varying degrees, toxic to man and to wild and domestic animals, caution must be exercised in their use, and the manufacturers’ directions must be closely followed. The use of many pest control chemicals is restricted, and the service of a professional pest control firm is required for their application.

This section covers the most common mammalian pests encountered in buildings. The guidelines for dealing with these pests may be applicable to other species. Before dealing with an unfamiliar animal, check local and national regulations on its status. Many fur-bearing mammals are protected, but this does not necessarily exclude the possibility of trapping or destruction if they are a persistent threat to a property. Live trapping may be considered. The animals may be subsequently released at some distance from the building. However, such subsequentrelease is not permitted for introduced species such as the grey squirrel.

Exclusion of mammalian pests

Most authorities stress that prevention by exclusion is the most effective long-term solution to a mammalian pest problem. The following precautions will discourage entry of rodents and other small animals into a building.

Eliminate food sources

Keep food out of the building or, at least, in sealed metal containers. Keep garbage in an enclosed area away from the building. Practice good housekeeping methods in kitchens, cafeterias and lunch rooms. Clean spills immediately and thoroughly.

Eliminate sources of drinking water

Eliminate sources of drinking water by repairing leaky pipes and taps, and by covering open drains with heavy screens using 6mm galvanized wire mesh (16 to 19 gauge). Prevent the formation of condensation on cold pipes by installing pipe insulation.

Block off entry points

Ensure that doors and windows are tight-fitting and latched. Secure all vents and louvres, and cover openings with 6mm galvanized wire mesh. Ensure that attic vents are screened. Use sheet metal or concrete to block off all small openings to the outside, particularly in the foundation and ground floor of a building. Exclusion methods must not interfere with normal ventilation of buildings. Inadequately ventilated buildings can accumulate moisture, leading to fungal problems

Avoid clutter

Keep storage areas uncluttered and orderly, and inspect them frequently. Shelving and cabinets should be mounted a minimum of 10 cm off the floor to allow for thorough cleaning and inspection and to discourage pests from residing there

Prevent entry by climbing

Cut back any overhanging branches to beyond 3 metres from the building, and remove any climbing plants which animals could use to gain access at upper levels

Deter animals from living close to a building

Dig up, disturb or remove nesting sites, burrows and hiding places. Eliminate from around buildings all undergrowth and debris, which can provide protective cover

Refuse management

Keep all refuse, especially food matter and material suitable for nesting, in secure, rodent-proof containers. If practicable, avoid leaving plastic refuse bags out overnight

Species of mammalian pest

Correct identification of the pest causing the problem in a building is essential for choosing an effective solution. Use field guides to aid this identification. Apart from rodents, the following animals may be encountered

Feral cats

Feral cats live on discarded food, rats, mice and birds. Being extremely timid, they may occur in quite large numbers without often being seen. They generally cause little damage, but they may introduce cat fleas into buildings, especially in their sleeping places

Squirrels

Squirrels are generally only a minor irritation, but they have been known to chew cables and electrical wiring. They can create much noise and disturbance, can introduce parasites and may bite fiercely if cornered. They may be deterred from climbing trees or walls by placing a 2 feet wide metal band around the tree or on the wall, about 3 to 4 feet above ground. They may be repelled from entering roof and other spaces by spreading napthalene: physical exclusion is preferable wherever possible. Note that grey squirrels are an introduced species, and consequently, if they are caught alive in a trap, they must not be released at some other location

Rodents, Rodentia

Rats and mice are potentially damaging in both urban and rural settings. These animals may also carry diseases that can infect man through bites or by contact with hair, excreta, or parasites, such as fleas, lice, and mites

Natural history of rodents

Two types of rat are found in Britain, the black rat, Rattus rattus, and the brown or Norway rat, Rattus norvegicus. The brown rat is larger, more heavily built and agressive than the black rat and has consequently ousted the black rat from most habitats. However, the superior climbing abilities of the black rat allow a degree of co-existence. In Britain, the black rat is mainly confined to sea ports

Both species are omnivorous, but the black rat prefers vegetable food. Except in rapidly expanding populations (where white and black individuals are common), the brown rat is almost universally brown, with a paler underside. The black rat varies in colour from tawny yellow to black

Mice are found in perhaps the majority of homes around the world, in addition to food stores, agricultural land etc. Mice often enter buildings in autumn to overwinter, and constitute a common rodent problem

Brown rat, Rattus norvegicus

Brown rat, Rattus norvegicus (Norway, Common, Sewer, Wharf or House Rat) Total length 30 to 45 cm Weight 200 to 550 grams Colour Brown or reddish-grey with a lighter grey belly Nose Blunt Ears Short and thick Tail Shorter than head and body lighter underside rough and thick Reproduction Sexually mature in 8 to 12 weeks average 24 young per year Females have 12 mammae Food Omnivorous Droppings Capsule-shaped average 20mm long 40 to 125 passed daily Range worldwide Habitat Individuals range over half a kilometre outdoors, and often along established runs indoors burrow approximately one metre underground or inhabit lower levels of buildings good climbers and swimmers, and can jump heights to 80cm and gaps to 1.5m

Black rat, Rattus rattus

Black rat, Rattus rattus (Roof or Ship rat) Total length 42cm Weight Up to 300 grams Colour Black or brownish-grey with a lighter belly Nose Pointed Ears Thin and large Tail Slender, longer than head and body Reproduction Sexually mature in 12 to 16 weeks capable of a litter every 3.5 to 4 weeks fewer young per year than R. norvegicus Females have 10 mammae Food Omnivorous Droppings Tear-drop shaped average 12mm long Range ports and coastal areas Habitat Individuals usually range within 100 metres prefer upper levels of buildings good climbers and swimmers, and can jump 1.5m

House mouse, Mus musculus

House mouse, Mus musculus Total length 17.5 (body, 8.5 cm tail, 9cm) Weight Up to 25 grams Colour Brownish-grey with grey belly Nose Pointed Ears Large Tail Longer than body dark in colour Reproduction Sexually mature in 5 to 12 weeks capable of a litter every 3.5 weeks to 4 weeks, and up to 60 young per year Food Omnivorous but prefer cereals Droppings 6 mm long narrow Range worldwide Habitat Individuals usually range less than 12 metres from nest; can pass through 10mm (3/8″) hole enter buildings in fall for shelter during winter inhabit enclosed spaces such as wall cavities burrow 20 cm deep excellent climbers, good swimmers, and can jump 30 cm

Field mice (several species)

Field mice are protected wild animals. They may occasionally enter buildings in the autumn or winter. The mice, if identified, should not be poisoned, but should either be ignored, or caught alive in special traps, and subsequently released in the countryside

Rodent control

Rodent infestations create considerable hazards for buildings, their contents and their occupants. Prevention of infestations should be approached from three angles
discouragement of entry into buildings, prevention of access to food and water, and destruction of animals which do gain entry. Destruction of external animals is of limited usefulness, except where the external population is high and its food supply is limited, resulting in unusually determined attempts to enter buildings. However, removal of shelter close to buildings can help reduce the external population, and discourage attempts to gain entry

Identifying a rodent problem

The following signs, often evident before rodents are even seen, indicate that rodents are present

Tooth marks and gnawing

Tooth marks from gnawing
wood chips near baseboards or cabinets
or irregular losses, tears, or soiling of fabrics. Rodents engage in gnawing to wear down their constantly growing incisor teeth, to gain access to food, and to make nests. Most soft materials, including aluminium, asphalt, and lime mortar, are susceptable to rodent knawing

Faecal droppings

Droppings are produced in large numbers and will dry in one or two days. Rat droppings often contain hair. Because of the possibility of disease, do not handle rodent droppings directly
wear gloves or use a dustpan

Urine droplets

Urine deposited as small dribbles or as a line of droplets. Dried rat urine stains may not be visible to the naked eye, but will fluoresce blue-white under ultraviolet illumination. Avoid contact with urine. Use germicidal janitorial detergent to clean rodent urine off surfaces

Grease marks and dirt

Greasy smudges on wals, beams and pipes deposited from dirty and oily rodent fur. These marks are only visible in high traffic areas, or around holes etc, where the animals have had to squeeze against a surface to pass

Nests of shredded material

Nests made from shredded material, such as paper or textiles. Nests will usually be found in dark, dry, sheltered, and undisturbed areas, and are usually well concealed

Paw prints

Tracks of paw prints on dusty surfaces. Apply a non-toxic tracking powder, such as talc (not flour), along walls or suspected runs, and observe for several days to confirm the presence of rodents. Inspect the tracking powder with a raking light to enhance the visibility of the tracks. The front paws of rodents leave tracks showing four toes, the rear paw tracks are elongated and have five toes, and the tails leave short lines as marks

Burrows or holes

Burrows in the earth around buildings, or holes in the building foundations of 100mm in diameter that were made or enlarged by rodents. Rat nesting and access burrows are usually less than 1.2m deep. Fill in burrow entrances and check for excavation on the following day to determine if they are in use

Sounds of gnawing, squeaking, or scampering

Sounds of gnawing, squeaking, or scampering in walls. Sounds will be heard mainly at night unless the rodent colony is overpopulated

Odour

Rats have little odour unless the population is large or well established. Mice can often be detected by their musky odour

Live or dead rodents observed

Live or dead rodents seen in the building. Do not handle live or dead rodents with bare hands
see precautions described below

Capabilities of rats

Rats are able to
gain entrance through any opening larger than 13mm square
Climb both horizontal and vertical wires and cables
Climb the inside of vertical pipes which are 40-100mm in diameter
Climb the outside of vertical pipes and conduits up to 75mm in diameter
Climb the outside of vertical pipes of any size if the pipe is within 75mm of a wall or other continuous support for the rodent
Crawl horizontally on any type of pipe or conduit
Jump vertically as much as 1 m from a flat surface
Jump horizontally 1.2 m on a flat surface
Jump horizontally at least 2.4 m from an elevation of 4.5 m
Drop 15 m without being killed or seriously injured
Burrow vertically in earth to a depth of 1.25 m
Climb brick or other rough exterior walls which offer footholds to gain access to upper storeys of structures
Climb vines, shrubs and trees, or travel along telephone or power lines to gain access to upper storeys of buildings
Reach as much as 330mm along smooth, vertical walls
Swim as far as 0.8 km in open water
dive through water plumbing traps and travel in sewer lines even against substantial water currents
Gnaw through a wide variety of materials, including lead sheeting, lime mortar, aerated concrete blocks and aluminium sheeting

Capabilities of mice

Mice are able to
jump to heights of 800mm
Jump gaps of 1.5m
Gain entry through 8mm holes
Burrow up to 1m underground
Travel up to 0.5 km from their nest
Climb up pipes and wires
Swim
Survive on as little as 1ml of water per day while eating dry food

Additional exclusion methods

Total exclusion of rodents may not be cost-effective, but deterrence of entry most certainly is. Apart from the general exclusion methods detailed above, the following techniques may also be necessary

Metal cladding

If rodents are gnawing at wooden doors or window frames, apply sheet metal cladding as a deterrent

Prevention of climbing

Place large sheet metal cones (300mm long and 450mm in diameter) on exterior pipes and poles at a height of 2.5 metres to prevent the animals jumping past the cones and climbing up to points of access. Fasten 400mm squares of sheet metal over small pipes and wires that run up walls. Caulk gaps between sheet metal guards and wires to prevent mice crawling through

Poisoning and trapping

Poisoning and trapping are most effective when combined with suitable exclusion measures. In general, trapping is more effective for mice, while poisoning works better with rats. Trapping has the advantage that it prevents the rodent from dying in an inaccessible location where it will produce a foul smell and attract insect pests. Live trapping is possible
the animals may subsequently be released at some distance from the building, or killed by fumigation

Rat baits and poisons

Rats are inquisitive
they are also creatures of habit. Traps and baits should be laid on well used runs. New traps, or unaccustomed food sources will be treated at first with caution. If regular inspection of traps or baits is possible, unpoisoned bait or unsprung traps should be first laid. Once the rats have become used to them, add poison to the bait, or set the trap springs.
In the case of poison, it is essential to lay enough so that every rat that eats it receives a fatal dose, as any surviving animals will be warned off such baits. Extreme care must be taken to ensure that the carcases of poisoned rats are either removed and buried or burned, or else that they are completely inaccessible where they die, otherwise dogs, cats, pigs and wildlife may also be poisoned

Suitable baits for rats include bacon, raw or cooked meat, fish, peanut butter, fresh bread and oatmeal

Mouse baits and poisons

Mice are much less sociable animals than rats, and their feeding habits are very different. A rat, on finding food to its taste, will gorge itself until either it can eat no more, or the food is exhausted. Mice, however, nibble, rarely taking more than a few mouthfuls at a time from each source of food. Mice are also highly territorial, and the males constantly patrol their territories. Consequently, mice are much easier to trap than rats, even with unbaited traps, but they are much more difficult to poison. Bait shyness develops rapidly, and even with Warfarin-type baits, it is difficult to persuade the animals to eat enough over a period to be lethal

Suitable baits for mice include fruit, cake, peanut butter, seeds, sugar candy, gum drops and oatmeal

Traps

The snap trap, also called the guillotine, spring or break-back trap) is cheap, effective and widely available. Since it usually kills instantly, it is perhaps the most humane of all rodent control methods. Considerable suffering, however, can be caused if the animal is not killed but caught eg by one of its limbs

Traps must be placed out of the reach of the public, especially children. Traps should be placed near holes or runways, or at sites of previous damage. Ideally, traps should be secured in place to prevent them from being dragged away by a trapped animal. Keep a record of places where traps are laid in order to prevent their being accidentally tripped.

Traps should be checked daily. Take care when setting traps – traps, particularly those for rats, can break a finger if accidentally tripped

Anticoagulant poisons

Anticoagulant poisons, the best known of which is warfarin, cause the animal to die of anaemia after prolonged internal bleeding. Repeated dosage over five days is needed. The animals are said to feel no discomfort and hence are not usually warned off the baits. Warfarin resistant strains of rats have been reported, so higher dose baits may sometimes be needed. However, it has been suggested that so-called ‘super-rats’ are not so much resistant as wise to warfarin baits

Wild and domestic animals are unlikely to be harmed as a result of eating a single rat poisoned by Warfarin. However, where a large population of rats is gradually killed off, repeated scavenging of the carcases may result in an animal receiving the lethal repeat dose

Acute poisons

The most frequently used acute poison is fluoroacetamide, sold under the trade names ‘Fluorakil’ and ‘Compound 1081′, usually as cereal bait. It is extremely poisonous with a LD50 dose of 15 mg/kg for rats, considerably less for dogs. The chemical is a colourless, crystalline solid, very soluble in water, and odourless and tasteless. No antidote exists, and it is readily absorbed through cuts and abrasions, so great emphasis must be placed on safe handling and storage. Under the Poisons Rules 1970, its use in Britain is restricted to sewers, drains, docks and some other areas where human access is controlled

Other acute poisons include strychnine, phosphorus paste, zinc phosphate and sodium fluoroacetate

It is essential when laying baits with this type of poison that sufficient is eaten by the animal to kill it outright, otherwise bait shyness develops. As a consequence of the large dose which may be ingested, a relatively small amount of poisoned rodent eaten by a much larger scavenger (eg a dog), can prove fatal

Carcases of animals killed by these poisons must be incinerated or securely buried

Antidotes to poisons

No antidote exists for acute poisons, eg fluoroacetamide. Vitamin K acts as an antidote to anticoagulant poisons. In the event of accidental ingestion of the poison, Vitamin K should be administered under medical or vetinerary supervision

Fumigation

Fumigation should only be resorted to when all other methods have failed. The bodies of the animals remain in inaccesible locations, where their decay is likely to cause health problems. Fumigants may also damage building contents

Animals trapped in their burrows, or inhabiting air-tight buildings may be killed with fumigants such as methyl bromide, chloropicrin or calcium cyanide. These may only be used by registered pest control officers

Carbon dioxide fumigation, in a sealed container, may be used to dispose of animals caught alive in traps, which are not intended to be released. It is regarded as the most humane method of killing such animals

Diseases spread by rodents

Rats can spread disease both directly and indirectly. Food poisoning organisms such as Salmonella may be spread via rat faeices and urine. Weil’s disease, a severe and often fatal form of jaundice, is spread, particularly in water, by rat (and less often mouse) urine. Mouse faeces may spread tapeworms

Plant growth and buildings

There is a tendency in the building industry to regard plants, and particularly trees, with suspicion, if not outright hostility. Building users, on the other hand, tend to welcome plants in a building’s environs. While plants can damage buildings, or more often, exacerbate the effects of building defects or poor maintenance, they can also protect. They are also the most cost effective decoration available

Plants growing in the environs of a building benefit not just the users of the building, but the whole community, and also wildlife. This can have legal and planning implications. Careful management of plant growth not only enhances the aesthetic benfits of the plants, but also reduces or removes most of the associated problems

Plants, building users and building owners

Plants can improve the appearance of a building, and the local microclimate, but plant growth has structural and legal implications for building owners and landowners

Structural considerations

Buildings can provide plants with support, or a place to grow undisturbed. Damp masonry and accumulations of debris can provide a substrate in which roots may grow. Plant growth, whether deliberate or accidental, can in some circumstances protect buildings, and in other circumstances damage them

The presence of plants can reduce the rate of drying, block ventilation holes, further the accumulation of debris, lead to the raising of external ground levels, and provide protection and cover for animal pests of all types. The most common problems are caused not but the plants themselves, but by dead leaves and other matter building up in rain and other drainage channels. Ultimately, however, such problems are due to building defects, poor maintenance, or poor management of plant growth

Plant cover can reduce erosion by wind and rain, reduce the force with which draughts and rain can penetrate a building, and reduce the rate of cooling of a building at night

Plants may cause direct damage
roots and shoots can exert very great forces when penetrating masonry and other surfaces. Plants, especially trees, growing in the vicinity of buildings may also have adverse effects
disturbance of ground water by trees, fire risk, lightning hazards and physical damage, especially in relation to storm damage

Plant growth over boundaries

Landowners are obliged to cut back plant growth where it interferes with the safe passage of vehicles or pedestrians

When plants are growing over neighbouring properties, the owners of the neighbouring properties are entitled to cut back the plants at the boundary line, regardless of whether (in the case of trees) this is compatible with good arboricultural practice

Landowners are responsible for any damage caused by plants growing within their property, eg trees falling onto neighbouring highways or properties

Poisonous plants

Where the public has right of access, or a poisonous plant grows over the boundary, landowners are responsible for its effects. For example, if a neighbour’s animals are poisoned by eating yew growing on or over the boundary, the the landowner is responsible for the consequences. However, the landowner is not liable if the animals are poisoned as a result of straying or stretching into the land – unless the landowner has a responsibility to maintain the fences, and the poisoning was the result of the landowner’s failure to do so. Local authorites have been held responsible for deaths by poisoning as a result of children eating the berries of poisonous plants growing in parks and botanic gardens. Presumably, this responsibility applies to plants growing on any land to which the public has access, or a right of way exists
Glasgow Corporation v Taylor, 1922

Plants and planning and other restrictions

Tree Preservation Orders are discussed below

The planting or the retention of plants, trees or gardens can be a condition of planning permission, or can form part of the conditions governing a conservation area. Under the National Heritage Act 1983, English Heritage may include parks and gardens on the ‘Register of Historic Parks and Gardens’. The register has no statutory effect, but local authorities are said to give ‘a fair degree’ of weight to it

Sites of Special Scientific Interest may be declared around existing or proposed buildings. Under the 1981 Wildlife and Countryside Act, this is the responsibility of English Nature (formerly the Nature Conservancy Council), if it considers that the land is of special interest because of its flora, fauna, geological or physiographical features. After recommendations are made to the local planning authority and the Secretary of State, the site is given special protection against any activity that could harm or destroy the item of interest. Under the Act, 93 types of plant are currently protected, with special protection for birds, wetlands and forestry

Climbing plants

Most types of climbing plants can use a building for support
often this has a decorative effect so that the plant growth may have been welcomed or even initiated by the building owner. The appearance of a many a grim structure has been improved by the growth of flowering plants or creepers, but if plant growth is permitted at all, it must be very carefully managed, and its effects carefully monitored

Climbing plants and moisture

Opinions differ over the effect of climbing plants on the moisture balance of buildings. Some feel that the overall effect is negligible, while others feel that climbing plants should be avoided at all costs. Neither school of thought appears to be supported by actual measurements.

Plant growth may cover up ventilation channels, especially air bricks and vents for under-floor spaces and roof voids, especially at the eaves. If vegetation is to be permitted, these ventilation channels must be regularly checked and cleaned

Deciduous, and to a lesser extent evergreen creepers can deposit large quantities of dead leaves, petals or even fruiting bodies into rain and other drainage channels, leading to their blockage and subsequent water ingress into the building. Regular inspections are therefore a necessity when creeper growth is permitted. When specifying for new building or building refurbishment, it is advisable:
i) to make arrangements to assist access for inspections
and
ii) to specify larger rainwater drainage gutters, downpipes etc than would otherwise be strictly necessary

Plant growth, especially creepers, can cover up damp problems arising from unrelated building defects such as leaking gutters, downpipes or cistern overflow. The fact that damp problems go unnoticed, and hence uncorrected, is arguably the most serious of the potential problems caused by creeper growth on buildings

Plant growth involves the transport of substantial quantities of water up from the roots to the leaves, where the water evaporates. Even in the hottest, dryest weather, the building is surrounded by a cool, damp envelope. In poorly insulated buildings prone to overheating, building occupants may see this as an advantage, and in hot damp weather, the effect on the building moisture balance may be positive

While it may be true that a dense covering of leaves may repel light rain, it has been argued that the net effect of vegetation is to make the external walls of a building damper. In heavy or driven rain, vegetation does not prevent water penetration, but it can in principle impede water run-off, and by cutting out sunlight and impeding air circulation, vegetation can slow the drying off process when the rain has stopped. Without actual measurements it is not possible to establish the veracity of these claims

Older buildings without damp proof courses depend on the evaporation of water from the surface of the masonry. Dense vegetation may impede this evaporation, causing dampness in the walls

Root damage and climbing plants

Inevitably, the roots of climbing plants will be close to the building, where they may damage masonry and foundations. Damage may include:

  • disturbance of foundations as a result of localised withdrawal of water from around the foundations
  • physical displacement of foundations and masonry components as a result of the increasing girth of the roots
  • penetration of joints and cracks in drains and water courses, leading to blockage or leakage – such penetration is usually the result of an underlying defect, eg the cracking of clay waste pipes as a result of ground movement
  • Above ground physical damage from climbing plants

Physical damage may include:

fire risk. The leaves and stems of evergreen creepers such as ivy can burn fiercely, and enable a fire to be carried on the outside of a building to areas that might otherwise be unaffected by the fire. Deciduous creepers may build up dead leaves, birds’ nests and other debris, with much the same effect

storm damage. Creepers on the surface of a building marginally increase its wind resistance, and thus the likelihood of damage in a storm. Creepers may also be blown off in a storm, causing damage in their fall, or bringing with them items such as gutters or downpipes

damage to surfaces. Creepers such as ivy put out rootlets which adhere strongly to the surface on which it is growing, and which may be very difficult to remove without either damaging the surface, or leaving highly visible areas of woody deposits. Paint is particularly vulnerable and may be stripped off by contact with ivy

interference with drainage. Growth of creepers can block gutters and spouts and other rain drainage routes, leading to blockage and subsequent water penetration into the building. Deciduous creepers also deposit large quantities of leaves directly around the building

displacement of building elements. The shoots of creepers can displace slates, coping stones, bricks and other elements, causing water penetration through roofs, water penetration into walls, and in extreme cases, creating a risk of masonry elements falling off

problems with lofts. Creepers can block ventilation routes, either by growing through them or over them, or as a result of the build up of debris. Shoots growing into loft spaces may cause further damage in attempting to grow back towards the light

pests. Creepers provide cover for all manner of animals which may cause a nuisance in buildings – flies, wasps and other insects, sites for birds to nest and roost, and parasites associated with this, and lead to periodic invasions of normally harmless creatures such as spiders. In addition, vegetation can provide high level access for rodent pests, which might have been successfully excluded at ground level

General recommendations

The growth of climbing plants on buildings may be desirable for aesthetic reasons, but there are no other proven benefits. If the building owner feels that the aesthetic benefit justifies the physical disadvantages, the following management steps must be taken:

check the building detailing. Ensure that gutters and downpipes are firmly fixed and adequately sized. Ensure that cladding and other surface finishes are sound and firmly affixed

choosing where to plant. Plant in clear ground, well away from drainage pipes or other water-containing services which may be damaged by root action

site preparation. Before considering planting, bear in mind that ground levels must be at least 150mm below dpc level, and that dpc bridging by plant stems, soil or debris must be avoided. Soil near buildings is seldom at its most fertile, and it may be necessary to import humus to enable healthy plant growth. As the plant grows, ground levels around it will tend to rise, for which allowance must be made. Often it will be necessary to dig out the soil first

trimming. It is essential that the growth be regularly trimmed so that growth remains well away from windows, ventilators, areas of delicate finish, and well below the level of the eaves

on no account must the building owner permit growth over gutters or roofs, or into the eaves or any other point of entry into the building

large, well established rootstocks should be avoided as these are more likely to cause problems. Regular and drastic pruning above ground helps reduce the rate of increase in the diameter of roots

Types of climbing plants

Weeds

A weed has been defined as a plant growing where it is not wanted. For present purposes, however we shall use the word for small herbaceous plants growing in a building environs. Unlike climbing plants, herbaceous plants are not generally wanted in or on a building, let alone introduced there, by the building owner

Weeds are often a sign of other underlying building defects. Weeds may grow from seed in damp masonry, in accumulated debris in gutters, and other areas where ponding has occurred, such as flat roofs, and in yards and other exterior areas. Existing weeds in the ground, if not killed or removed before building work starts, may damage asphalt, masonry and even concrete in their attempt to grow out into the light

Weeds growing in masonry

Weed growth in masonry indicates chronic water ingress into the masonry, which has also resulted in deterioration of the mortar. Weeds, and as much mortar as is practicable must be removed, and sources of water ingress such as leaking downpipes, defective coping, defective flashing or roofing, should be rectified. When the masonry has dried out, and all signs of plant growth have ceased, the masonry should be properly pointed

Weeds growing in roofs and gutters

Weed growth in roofs and gutters indicates poor detailing or maintenance, resulting in ponding of water, or the build up of debris. Debris may build up as a result of bird action, and moss and other matter falling off roofs. Weed growth increases the rate at which soil and other debris accumulates. Weeds and the soil or debris in which they are growing should be removed during regular inspections, and any faults in the detailing should be rectified

Regrowth of existing weeds

Weeds with strong root or rhizome structures such as dandelion, dock, bindweed and ground elder can break through asphalt, paving and even concrete laid on top of them. Such rootstocks are difficult to remove by mechanical means. If they are present, long acting herbicides should be used.

Mosses and lichens

The growth of mosses and lichens on buildings is frequently welcomed for aesthetic reasons. However, moss growth in particular may have a number of undesirable consequences:

  • surface erosion – as a result of physical adhesion and chemical breakdown of surface by rootlets of moss
  • water retention. Mosses in particular inhibit drying and retain moisture, increasing the chance of frost damage to masonry and roofing materials
  • blockage of rain drainage channels. Moss falling off roofs can build up in gutters and block spouts and downpipes
  • encouraging other plant growth. Mosses and lichens, and the build up of soil around them, can provide areas in which seeds of destructive building weeds such as Buddleia can germinate, and having germinated, cause serious damage to building facbric

Fungi and bacteria

Older classifications place fungi and bacteria in the plant kingdom, but they are now generally regarded as two separate kindoms, separate from both plants and animals. Apart from timber decay organisms, the main problems caused by bacteria and fungi in buildings are related to the health of the occupants

Timber decay fungi

See timber decay document.

Mildews and other fungi

See timber decay document.

Bacteria

See environmental health section

Trees

Trees are sometimes regarded as a nuisance near buildings. They can be blamed for subsidence and heave, they can block drains and gutters with their leaves and occasionally as a result of root penetration, and they can attract the attentions of officialdom in the form of Tree Preservation Orders. On the other hand, trees have great amenity value, and they can protect a building against snow cover, and from the wind. Conifer trees to the north and deciduous trees to the south can help make a building warmer in winter and cooler in summer

Trees growing within buildings

Trees and building structures

Trees and ground water

Trees can draw large amounts of water from the ground around buildings. In areas of clay subsoil, the increased growth, or the removal of trees can contribute to the localised expansion or contraction of the clay, with possible harmful effects or subsidence or heave on a building structure

Trees growing close to buildings

Trees on balance enhance a good building, but they can also exacerbate a building’s defects. Not entirely surprisingly, the issue is contentious

Trees growing close to buildings:
benefits

Trees growing close to buildings can have beneficial effects:

  • shelter from strong wind and driven rain, consequently reducing water penetration, wind borne erosion, interior draughts and hence heating bills
  • protection of buildings from ‘cold air drainage’ at night
  • shelter from the heat of the summer sun
  • improved appearance and greater comfort, and an enhancement of the value of a building which more than offsets the possible financial disadvantages of the presence of trees in the proximity of a building
Trees growing close to buildings:
risks

Trees growing close to buildings can have harmful effects:

  • structural damage due to the removal (or the cessation of the removal) of groundwater
  • structural damage due to the increase in the physical girth of the tree or of its major roots
  • structural damage due to the tree, or part of the tree falling onto the building
  • increased risk of lightning damage as a result the tree being higher than the building, and hence more likely to be struck. This can result in side-strikes from the tree to vulnerable parts of the building, and, in the case of more combustible trees such as conifers, there is also a definite risk of fire following a strike
  • shading of the building from sunlight, rendering the building darker, colder and damper than it otherwise might be
  • root penetration can severely damage drains, particularly older ceramic pipes with cement joints. Rootlets can penetrate and force open cracks in the pipe or its junctions, arising from ground movement or deterioration of the cement junctions, leading to both blockage and leakage of the drains
  • blockage by dead leaves and other tree derived debris is one of the main reasons that gutters and downpipes become blocked, resulting in water overflowing into the building structure. Such blockage can arise for other reasons. If problems arise, the owner’s first response should be not to remove the trees, but to provide adequate and properly maintained rain drainage systems
  • trees near buildings can provide a means of entry for rats and mice, and can attract roosting pest birds such as pigeons, starlings, sparrows and rooks
  • trees growing in built up areas can attract Tree Preservation Orders, which can restrict the building owner’s options in exercising what he considers to be proper management of the trees. However, such orders are not applied unreasonably, and they do induce the owner to seek proper advice on the best means of managing the trees, rather than acting rashly on the strength of uninformed prejudice. Owners irritated by the restrictions posed by TPOs should remind themselves that trees imrpove the appearance of an area, and hence the value of the properties within it

Trees and legal responsibility

Landowners are responsible for the safety of the trees growing on their land. While it is accepted that trees may have hidden and unforeseeable defects, legal liability can apparently be established, if, with the benefit of hindsight, an expert arboriculturalist could reasonably have been expected to have observed the defect which caused the tree (or part of it) to fall. However, it would appear that the owner has an additional duty to observe and care for the trees – it is not enough merely to ‘hire an expert to cover one’s back’. A higher standard of expertise appears to be expected from knowledgeable and well funded bodies such as the National Trust, than is expected of private individuals

Trees and legal responsibility:
case law

Landowners are liable for injuries caused by defective trees to persons entitled to access to the land. In <<1>>, a boy was injured as a result of the collapse of a tree on which he was climbing

In <<2>>, the bough of a tree overhanging a road fell and damaged a motor coach. The tree had been inspected the previous autumn by a competent woodman and no defect had been found. The defect was latent and could not have been noticed in a reasonable inspection

Case <<3>>, a tree owned by the National Trust fell onto a road causing an accident which resulted in serious injury. The court held that the Trust had a ‘special duty of care’. It was ‘not expected that they should have the knowledge of an expert arboriculturalist, but something more than the ordinary countryman’. The Trust had employed experts to look at the trees, but some thinness of foliage and dieback had not been noticed
1. Cronin v Slough Corporation, 1975
2. Noble v Harrison, 1926
3. Quinn v Scott, 1965

Trees and legal responsibility:
statutory provisions

Highway authorities may require owners to cut back trees or shrubs which grows over the highway, thus causing danger to or impeding the passage of vehicles or pedestrians. Similar provisions exist for trees, hedges or dead planting which damage the highway, or which make the highway dangerous by excluding the sun or the wind

Trees and legal responsibility: tree preservation orders

Tree Preservation Orders (TPOs) are made by local planning authorities ‘in the interest of amenity’. TPOs prevent the cutting down, topping, lopping, uprooting, and deliberate damage or uprooting of trees without the consent of the local planning authority. Trees growing in conservation areas are given much the same statutory protection, even though they may not be individually listed for protection. Unlike TPO provisions, planning rules can enforce the planting of new trees, or the replacement of trees felled for whatever reason

There clearly comes a point when a seedling or a sapling becomes a tree, but this point was not defined in the TPO legislation. Lord Denning suggested during the case <<1>&gt
that a tree be defined as having a main trunk diameter of six or seven inches

The penalty for destroying or damaging trees protected by TPOs is a fine not exceeding œ2000, or twice the value of the tree destroyed or damaged

There are exceptions to the rule, which allow the felling of protected trees:

  • the trees are dead or dying, unsafe, or have become statutory nuisances
  • woodland schemes approved by the Forestry Commision
  • trees cut down under a felling licence from the Forestry Commision
  • tree on local authority land, felled with the local authority permission
  • trees not exceeding 75mm in diameter
  • trees not exceeding 100mm in diameter if removed to help the growth of other trees

Although in these cases it is not necessary to inform the local authority of one’s intention to fell or lop a tree, it is usually advisable to do so. It may, for example, be quite difficult to prove that a tree was dangerous once it has been cut down and removed. In the case of a protected tree suddenly requiring urgent attention, for example after a storm, the evidence of an expert, or failing that, photographic evidence, should be obtained

It was noted that a disproportionately large number of trees subject to TPOs fell in the great 1987 storm. This was largely – but not entirely, on account of the greater average age of protected trees
1. Kent CC v Batchelor

Trees and planning enforcement

The retention or planting of trees can form part of the conditions of the granting of planning consent, and can form part of the area plans in conservation areas. Planning restrictions are at once more and less binding than TPOs. TPOs refer to individual trees
if the tree dies, or is destroyed, the landowner is under no obligation to replace it. With planning regulations, this is not necessarily the case, but on the other hand, the building owner may be obliged to replace the tree or trees, with similar ones

Characteristics of trees

Lifespan

The maximum lifespans in years of some common British species are as follows:

Species

Years of lifespan

Yew 1500
Oak 500
Sweet chestnut 450
London plane 400
Sycamore 400
Common lime 400
Horse chestnut 350
Walnut 200
Crack willow 100

Arboricultural Association method of evaluation of trees

For legal and accounting purposes, it is often necessary to calculate the amenity value of trees, using a system of points. This is based on a combination of measurable factors, such as girth, and subjective factors such as suitability for setting. Consequently, disagreement can be over whether a tree is worth say œ300 or œ400, but it is much less likely over whether a tree is worth œ300 or œ3000. This evaluation has little or no relation to the commercial value of the tree for its timber

The seven value factors

The following factors are used to make the analysis:

  1. Size: ‘small’ (3 – 10m2), ‘medium’ (10 – 50m2), ‘large’ (50 – 200m2), and ‘very large’ (over 200m2)
  2. Life expectancy: this depends on the age and type of tree, its position and its general state of health. An expert arboriculturalist may be required to assess this
  3. Scenic importance: ‘little’ importance (trees in woodlands, in groups or in back gardens)
    ‘some’ importance (individual trees by roads, in parks)
    ‘considerable’ importance (prominent individual trees in town centres, sopping precincts etc)
    and ‘great’ importance (trees of crucial importance as main features in a public place)
  4. Other trees present: ‘many’ (more than 10 trees in total or 30 per cent of the visual area covered by trees
    ‘some’ (4 to 9 trees in total or 10 per cent of the visual area covered by trees)
    ‘few’ (1 to 3 other trees present or less than 10 per cent of the visual area)
    and ‘none’ (no other trees present in the area under consideration)
  5. Relation to setting: a largely aesthetic judgement, depending on the size of the tree in relation to its surrounding, species, form, general condition and its contribution to the landscape
  6. Form
    an aesthetic judgement, but fairly self evident – badly mutilated examples, or tree suffering from storm damage or disease are classed as ‘poor’, while particularly elegant or well maintained trees are ‘good’ to ‘excellent’
  7. Special factors: these include matters such as unusual botanical or historical interest, rarity, or unique contribution to a landscape, such as the tree being part of an avenue, or the focal pont of a scene. Such trees may form an important part of the designation of a Conservation Area

Evaluation table for trees

To calculate the ‘amenity value’ of a tree, multiply all the points awarded to it together and then multiply the result by a conversion factor. In 1990, this was set at œ10.00

Conversion Factor

Points

1 2 3 4
a Size Small Medium Large Very Large
b Life expectancy 10-20 years 20-40 years 40-100 years Over 100 years
c Scenic importance Little Some Considerable Great
d Other trees Many Some Few None
e Setting Just suitable Fairly suitable Very suitable Esp. suitable
f Form Poor Fair Good Excellent
g Special factors None One factor Two factors Three + factors

Thus a large (a=3 points) oak tree (g=1 point), life expectancy 200+ years (b=4 points), forms an important part (c=3 points) of an avenue (d=3 points) in a country house park (e=4 points). The tree is healthy and symmetrical, but has been slightly damaged by lightning (f=2 points). It therefore has an ‘amenity value’ of œ10 x 3 x 1 x 4 x 3 x 3 x 4 x 2 = œ8640. These points are shown highlighted in the table.

Any tree which fails to score on any of the first five value factors is given a total amenity value of zero. Examples of such trees might be very small, very old, seriously rotten, or quite unsuitable for their surroundings.