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Pests in Buildings

Pests In Buildings
It is inevitable that pests will invade buildings from time to time. Some pests are unlikely to be of any real bother, particularly in small numbers (e.g. an occasional spider), but other pests can become a serious problem.

Problems resulting from pests in a building can include:

  • Deterioration of the building (e.g. rodents making holes, termites destroying wood).
  • People developing allergies (allergies to animals such as possums and rats, or dust mites, are common).
  • Pests can bring & spread diseases (e.g. flies, rodents).
  • Bites (from spiders, fleas, mosquitos, etc.).
  • Psychological affects

Hygiene is important to deter many types of pests. Pests enter a house in search of food, and will stay if they find food. If a pest is to enter a house it needs to have somewhere it can enter. Often the point of entry is only a small hole. If the point of entry can be found and blocked, this is perhaps the simplest method of control. Traps may be used in some cases, located near the point of entry. However, some native species might be considered pets so be sure that they do not become trapped within the walls if you block off the hole.

Dust Mites
Mites are small, eight legged animals related to spiders (Phylum arachnida). These pests are responsible for allergic reactions in some people, and, as they are microscopic in size, are difficult to identify. They are likely to be found in carpeted areas, bed linen and anywhere dust accumulates. They may also be responsible for spreading disease.

Mites also exist in the garden and therefore may be present in indoor plants.  They are often barely visible to the naked eye. They feed on a variety of plant and animal materials, and are active mainly during the warmer months of the year. There are also predatory mites that can be used to attack and control harmful species.

The flea prospers in dry, dusty conditions. The adults feed on blood from various animals such as dogs, cats, horses and pets but will feed on human hosts. The larvae feed on any organic material available from food crumbs to hair. They can cause rashes and spread disease. Once infestation occurs they can be very difficult to rid due to their cyclic breeding patterns.

When disturbed, tiny adult fleas will move very fast. They are readily seen, but not easily caught. They live in a wide variety of climates and under warm, humid conditions can breed to very large numbers both indoors and out in loose sand, soil or dust, on animals or long grass.


Ants tend to be a problem in areas where food preparation takes place i.e. the kitchen. Often they will be entering the building from an outside source and as such will resist localised efforts at their removal. Hygiene in the form of removal of food scraps, especially sweet foods will often be enough to deter them. Holes around doors, floors and windows should also be sealed.

Ants are a minor nuisance, but can sometimes become a very major problem, invading homes and other buildings. Some can actually be beneficial, particularly larger ants, attacking and killing other insects which are plant pests.

Problems can vary from minor to very serious:

  • Nesting in and destroying wood (e.g. seats, walls, buildings).
  • Biting people (some types give far worse bites than others).
  • Shifting soil, creating unsightly nests, undermining structures.
  • Moving from the garden indoors, particularly into the kitchen in search of foodstuffs.  Ants can carry various human diseases such as dysentery, salmonella and smallpox.
  • Nesting in container plants.

There are many types of ants; some are more destructive than others.  Different ones feed differently - some on wood (e.g. termites), some on other animals, some seed, fungi, sugar, food scraps or exudations from scale and aphis.

Eliminating ants can sometimes be a problem though in termite prone places. If the ants that attack termites are eliminated, the termites may then be free to attack structures without anything tempering their spread.

Common Types of Ants
Argentine Ant (Iridomyrmex humilis)
Light brown to brown, and around 3mm long. They are more destructive than most other species, feeding on many different things. They move in well defined trails, often moving to drier places in wet periods. Commonly nests under organic mulch or rotting timber. They prefer sweet food, but will eat many things, including meat, seeds, insects, and fruit.

Coastal Brown Ant (Pheidole megacephala)
Around 1.5-2.5 mm long and brown to light yellowish brown in colour. The soldiers have a very large head. They tend to nest in buildings; or in cavities between bricks, stone, concrete, and rocks. They feed mainly on animal matter (dead insects, meat, grease, etc.).

Pharaohs Ant (Monomorium pharaonis)
Grows to about 2 mm long, and are yellowish brown to brown in colour. They commonly nest in buildings, and can travel long distances for food. They prefer meats, fatty foods and any plant material, but can eat sweets also.

White Footed House Ant (Technomyrmex albipes)
Has a black body with pale amber feet. It grows about 2.5 to 3 mm long, nests both inside & out, and eats most types of food.

Black House Ant (Iridomyrmex glaber)
Grows to about 2.5 to 3 mm long, with a black body, nesting mainly outdoors, but sometimes in building cavities. It eats most foods.

Odorous Ant (Tapinoma minutum)
A brown to dark brown body, up to 2-3 mm long, commonly nesting in buildings, and eating all types of food scraps.

Carpenter Ant (Camponotus spp.)
A large ant 6-12 mm with variable colour, commonly nesting in wet or rotting wood, usually in bush or rural areas. It hunts for food mainly at night.


These pests can cause large scale structural damage to buildings, and if allowed to gain a foothold can make buildings completely unsafe and requiring demolishing. They are really only a problem in wooden structures.

These are not true ants and they are not always white. They create colonies in soil or wood (sometimes building large earth mounds). They can cause serious damage to timber.  They like high humidity and usually like temperatures between 20 and 24 degrees Celsius. Most termites eat grass and organic debris, but some species attack wood causing damage to furniture, floor boards, walls, struts, trees or timber walls or structures in the garden. These can be a problem. Dry wood termites don't usually need as much water. The nests tend to be more vigorous when temperatures outside are very hot or cold.

Control is difficult without either extremely poisonous chemicals, or else using woods which contain chemicals that deter termites. Alternatively wood can be treated with timber preservatives (e.g. treated pine, creosote soaked timber).

Woods naturally resistant to termites include:

  • Acacia acumibata.
  • Callitris collumellaris.
  • Castenospermum australe.
  • Eucalyptus camaldulensis.
  • Eucalyptus corymbosa.
  • Eucalyptus marginata (Jarrah) - resists most, but not all, termites.
  • Eucalyptus polyanthemos (Red Box).
  • Sequoia sempervirens.
  • Taxodium disichum.


The use of flyscreen doors and windows will keep this pest in check. Flies can be irritating and are known disease carriers. The strategic placement of certain plants (mint, fennel) around a building can deter flies as the scent of these plants repels them. The larvae (known as maggots) of a large variety of these winged insects. The adult flies of some species can also be particularly annoying to humans, and domestic animals (e.g. house flies).

General Control
Spray with Malathion or Pyrethrum. Plants that have been used in the past for centuries to deter flies include: garlic, tansy, citronella, pennyroyal.

House Flies (Domestic Flies)
A very common black fly, 4-8 mm long, prefers to breed in warm, moist organic matter (e.g. compost heaps, piles of lawn clippings, rotting food). Removing these breeding places is important to controlling numbers.

Sciarid Flies
These are tiny black flies that lay their eggs on decomposing organic matter. The larvae hatch and eat that organic material. These flies can be a problem with indoor plants and mushrooms in moist, highly organic potting mixes. The flies can be a real nuisance to humans. They are difficult to control.


Mosquitoes attack people mostly outdoors, but they certainly can be a problem indoors as well. Mosquitoes need still water to breed, so they are more likely to occur if you have a pond, dam (or even puddles of water) in the garden or nearby. Apart from discomfort, mosquitoes can transmit a variety of diseases including Ross River Virus, Malaria and some parasitic worms. They are more prolific in wet, warm conditions.

Control is best affected by disturbing or destroying breeding habitats. Be sure to stock ponds with fish and other animals which will attack and eat mosquitoes and their larvae. Be sure not to leave containers lying about the building which can collect water. Use natural repellents if mosquitoes are prevalent. Or cover up yourself with long sleeves and trousers.


There are many different types of wasps that can be found in the garden. Some are pests, some are predators of other pests, but some can sting and as such are undesirable. Wasps frequently build nests which look like a blob of mud. These may be found on the foliage or wood of a plant or even on the outside of a building. Unless the wasp is known to be dangerous (e.g. European Wasp), the nest may be left undisturbed so the wasps can help you destroy other less desirable insects.

Ichneumon Wasp
There are many different types of this wasp. They have long slender bodies, and feed on pollen and nectar; attracted to flowers in the garden. They lay eggs in the larvae of other insects, including aphis, caterpillars, and beetle grubs.

European Wasps (Vespula germanica)
Similar in size and shape to a bee, but less hairy and with a longer abdomen. They can be distinguished from a bee by a black body with lemon yellow bands. Unlike bees they can sting more than once. When disturbed the wasp will release a pheromone (a chemical signal) that attracts other wasps. Their stings can be very poisonous, and can cause serious reactions in some people, occasionally even death. They should not be swatted as this will only aggravate them. They are attracted to a wide variety of foodstuffs, including sweet foods, ripe fruits, meat, nectar, caterpillars, pet food, garbage and sweet drinks. They can create large nests of wood pulp in such spots as in the ground in gardens, in hollows in trees, in rockeries, in piles of rubbish, or in the walls or roofs of buildings. In some states this wasp is a gazetted pest requiring the owner or occupier of the land were the wasp nest occurs to be responsible for destroying it. This should ideally be done by suitably trained and equipped pest control operators. Your local council will usually have information on the control of these pests, or be able to recommend someone to you.


Cockroaches are scavengers, like ants. They are closely related to termites and are more of a pest in warm climates. The major problem is that they transmit human diseases. Some may bore into wood, or feed on roots or shoots. They like food scraps - so clean up. They eat a very wide range of things: virtually any food that people or other animals might eat including fabric, leather, paper and even glue.

They like protected places to breed - in wood heaps, under bark mulch, in loose bark of trees, behind dead palm fronds still clinging to palm trees. Control involves minimising such situations; and keeping these situations well away from the building.

Hygiene is extremely important. Not only inside but also outside.
Some animals, such as frogs, spiders, lizards, birds, and some wasps will attack cockroaches.


Millipedes are small animals which usually have up to a few hundred legs. They differ from Centipedes in that they have two or more pairs of legs per body segment, except for the first few segments at the rear of the insect’s head, while Centipedes only have one pair of legs per body segment. They are black with a hard, shell like skin, and eat rotting, dead and living vegetation, in particular the roots of seedlings, and can even cause damage to root vegetables such as potatoes or beetroot. They can become a pest after prolonged rain.

Control (Of Millipedes and Centipedes)
Some types of snail baits will have an effect (but not all).
Diatomaceous earth dusted over the garden may also have some effect to discourage millipedes and centipedes.

Millipedes breed in moist organic material such as mulch on garden beds.

Black Portuguese Millipede (Ommatoiulus moreletii)
This millipede has a smooth cylindrical body 20 to 45mm long. They have 50 segments, each with two pairs of legs. The adults range from slate-grey to black, while the juveniles are light brown with a darker stripe along each side. When disturbed, Portuguese millipedes often curl into a tight spiral, or will sometimes try to escape with trashing, snake-like movements. They occur in the southern states of Australia and have a tendency to rapidly multiply and invade buildings in large numbers.

Non-chemical: Although some spiders, beetles and at least one type of scorpion will eat millipedes, these have not controlled the pest naturally. A parasitic fly from Portugal is being developed as a control measure in South Australia. Thorough removal of damp, decaying leaves and other garden litter outside of buildings is important. Physical barriers can also prevent the millipede from entering houses.


Spiders attack and control many different insects and other small pests. For this reason, they should not be discouraged from the building surrounds unless they become a nuisance (e.g. in the case of some poisonous spiders, causing concern that someone may be bitten). Poisonous spiders are unlikely to bite unless disturbed and threatened, and, in most cases, there are treatments which can be administered. Large numbers though are an unnecessary risk.

The most effective procedures are to discourage spider habitats by keeping the garden free of rubbish. Also wear gloves and practice caution when working in areas where dangerous spiders may be present.

Some dangerous Australian & Asian spiders include:

Redback Spider
These have long legs and a large black ball like abdomen. The female usually (not always) has a red or light brown stripe on the back and can be to 1.5 cm long. The male is much smaller, less commonly seen, and does not bite. The species is widespread, throughout all of Australia and some other countries. Numbers may increase under hot dry conditions.  They seem to nest in junk, timber, under the eaves of the house, and along wooden fences. Removal or the cleaning up of the garden may help in reducing likely nesting areas.

Funnel Web
More than one species; they are black with reddish hairs; to 3.5 cm long. The Sydney Funnel Web dwells in holes in the ground; the Northern Tree Funnel Web dwells in holes in trees; both are aggressive and very toxic.

White Tailed Spider
Has a white marking on the end of a long tail. It is not deadly but will give a nasty bite.  Symptoms to humans are necrotic wounds that can be highly problematic in treating and often require skin grafts. Infected area may be quite large.


Rodents (Mice/Rats)
Rats and mice will use buildings for shelter and food. Scraps should not be left lying and even bins should be regularly emptied. These pests, along with being carriers of disease can also play havoc with electrical wiring which they chew through.   Rodents can be a serious pest invading compost heaps, store sheds or other parts of the garden where they can find shelter. They can move into a property from drainage pipes, bushland or other unattended places, in search of food and shelter.

Control can be achieved by the use physical (traps), biological (predators), and environmental (building design) means. Toxic alternatives, whilst relatively effective can create further unforeseen hazards, especially as far as children and pets are concerned.

Hygiene is essential to their control. Keep food items in sealed containers. Don't leave rubbish about. Be careful of pets and native wildlife when using poisons.


Birds can be both pests or of benefit around a building. They may nest in ceilings and walls. They are, however, an important means of control over insects and other pests. It is illegal to poison birds. It is also dangerous to poison birds (domestic pets may eat poisoned birds and themselves become poisoned). Birds nesting in buildings are a nuisance due to factors of excessive noise (especially during the breeding season), disease and as carriers of lice. From a positive perspective, birds should be appreciated for their aesthetic and natural worth by encouraging them to stay out of buildings but within the immediate vicinity. This can be done by bird baths and appropriately placed nesting boxes, and in some cases supplementary feeding.  

Cover areas you wish to protect with bird netting. Strips of aluminium foil, or light globes, can be hung in eaves to keep birds away from specific areas.
Provide alternatives for birds (e.g. nesting boxes in trees).


Generally snakes will avoid contact with humans and their dwellings, however, they sometimes will use buildings for shelter or, in cases of rodent infestation, a food source. It is a good idea in areas where snakes are likely to be found to create a barrier of open ground between the building and the surrounding vegetation. Snakes are very conscious of moving away from natural cover. Holes in floorboards or walls should be sealed.

Snakes will help control rodents, insects and some other garden pests. Snakes like many other pests will be encouraged by undisturbed long grass, piles of wood, rubbish or any other hiding places. By keeping the building surrounds clean, neat and tidy the likelihood of snakes will be reduced.

Disturbing nearby bushland sometimes chases snakes into your building and closer to homes. Snakes do not tend to like crawling over rough surfaces such as wood shavings, so using wood shavings as mulch may help deter them. They also do not like travelling over wide expanses of lawn as this exposes them to their predators.


Learn more about your environment - learn about healthy buildings, or about looking after plants.  Choose from a wide range of courses including:

Healthy Buildings I

Healthy Buildings II

Horticulture I

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