Spiders - pest control

Spiders are arachnids, a class of animal that includes scorpions, harvestmen, ticks and mites.

Spiders have two main body parts, eight legs, simple eyes, piercing jaws (fangs) and silk-spinning organs. Arachnids are different to insects. Insects have three main body parts, six legs, compound eyes, antennae and chewing jaws (mandibles). However, like insects, spiders have an exoskeleton that is shed periodically to allow the spider to grow, a process known as moulting.

Spiders play an important part in our environment, because they are essential to natural ecosystems. Some spider populations are threatened because of habitat destruction, but many spiders have adapted to live alongside humans in houses, sheds and gardens. Spiders usually feed on insects, making them quite beneficial to humans. Very few are harmful.

In Australia, there are about 2,000 described spider species. Even though most spiders are not aggressive, they may bite in self-defence if frightened, threatened or accidentally touched.

Spiders use venom to subdue their prey. Occasionally, this venom is used against a human in defence. Spider fangs are often unable to penetrate the human skin. However, some spiders that can bite humans may inflict painful and, in rare cases, dangerous bites.

Spider venom consist of a complex mixture of chemicals of biological origin. In humans, the effects of spider venom usually only causes localised pain and swelling, but may include:

• interference with blood clotting
• breakdown of muscle and tissue
• paralysis and effects on the cardiorespiratory.

Redback spiders and Sydney funnelweb spiders are the only two spiders that have caused deaths in Australia in the past. Sydney funnelwebs are not found in Victoria. Effective antivenom for redback spiders was introduced in 1956, and one for funnelweb spiders in 1980. There have been no deaths in Australia from a confirmed spider bite since then.

Common pest spiders

Redback spiders

Redbacks are found all across Australia, but are less common in the colder regions. They are often found in backyards.

The females build loose, untidy webs in dry, sheltered sites. The top of the web is funnel-shaped and this is where the spider hides. In the lower part there are sticky threads used for catching prey. There may also be up to 10 round egg sacs suspended within the web.

Redback spiders are black and shiny, with a red or an orange hourglass marking under the abdomen. Most also have a longitudinal stripe on the upper surface of the abdomen. They have long legs and a large, bulbous abdomen. Females (body length of about 10 mm) are significantly larger than males (body length of about 4 mm). Females live for 2–3 years and may produce several thousand offspring during that time. The males live for about 6–7 months – they are usually killed during mating by the female.

Due to their proximity to humans, hundreds of bites are reported each year. Only the female’s bite is dangerous and may require antivenom. As they are quite small, many redback bites are do not cause serious negative reactions in people.

Early symptoms of a redback bite include escalating pain, localised sweating, nausea and vomiting.

Whitetailed spider

Whitetailed spiders are found all across Australia. They usually live under bark and logs and in leaf litter, but they often enter our houses. These spiders are most active at night when they wander about hunting for other spiders, including black house spiders.

Whitetailed spiders do not make webs, but instead temporary silk retreats for moulting and egg laying. They have disc-shaped egg sacs.

Whitetailed spiders are grey to black with a cigar-shaped body and a distinct white mark on the tip of the abdomen. The female is about 18 mm long and the male is smaller, at about 12 mm.

Whitetails are not aggressive, but inflict a poisonous bite that is painful. Occasionally, local blistering or ulceration occurs, which could be due to a secondary bacterial infection.

There is little supporting evidence to link whitetailed spider bites with skin necrosis.

Funnelweb spiders

Funnelweb spiders are found around the east coast and the highlands of Australia (from Queensland to Tasmania) and small regions of South Australia. Most are found on the ground where they build burrows in moist, cool, sheltered areas, but some are tree-dwelling.

They are regarded to be the most notorious of the Australian spiders due to their highly toxic and fast-acting venom. However, out of at least 40 species, only the male Sydney funnelweb spiders have been responsible for recorded deaths.

Sydney funnelweb spiders are not found in Victoria.

The two Victorian funnelweb spider species are relatives of the Sydney funnelweb spider. However, their venom has been reported to cause only general symptoms such as headaches and nausea.

Trapdoor spiders, mouse spiders and black house spiders are commonly mistaken for funnelwebs.

The entrance to the burrow of a funnelweb spider has a funnel-like structure with one or two openings. Typically, the vibrations from silk triplines that extend across the ground alert the spider to possible danger or prey. Female funnelweb spiders spend most of their life in their burrows, but adult males wander in search of females, particularly during summer and autumn.

Funnelweb spiders have a shiny black head and legs, and black to brown abdomen covered in fine hairs. The females are slightly larger (35 mm) than the males (30 mm).

The female produces a pillow-shaped silk egg sac, which she defends vigorously if disturbed. The spiderlings hatch about 3 weeks later, and stay with the mother for a few months. Funnelwebs reach maturity in about 2–4 years. The females live for 10 or more years, whereas the males die 6–9 months after maturity.

Mouse spiders

Mouse spiders are widely distributed throughout Australia. The mouse spider lives in burrows in the ground, often near creeks and rivers, but is sometimes found in suburban gardens. The burrows are built with double trapdoors, which are set almost at right angles to each other. The females tend to remain in or near their burrows throughout their life, whereas the males wander during early winter, especially after rain. They are only rarely aggressive.

Mouse spiders are squat animals. They are 10–30 mm long, and the females are generally larger than the males. Their head area is high and broad with very large, bulbous jaws.

Female red-headed mouse spiders are dark brown to black, and the jaws are sometimes red-tinged. The males have a red head and jaws, and a blue abdomen. The eastern mouse spider’s males are black with a bluish white patch on the front of the abdomen.

The female lays eggs within an egg sac that she places into a brood chamber in her burrow. Males reach sexual maturity at about 4 years and then leave their burrows to find a mate. They wander during the day.

Some reports suggest that mouse spider venom may be very toxic. Fortunately, the bites usually cause only minor effects, but one serious poisoning has been recorded. Until more toxicity data are available, the bite should be treated as for a funnelweb spider bite.

Black house spider

Black house spiders are widely distributed in southern and eastern Australia. These spiders are naturally found in the bark of trees, but are common to urban areas and are often called window spiders. Their webs form untidy, lacy silk sheets with a funnel in which the spider sits. The female constructs several white egg sacs, which are secured within the web.

In the house, they feed upon insects such as flies and mosquitoes.

Black house spiders are robust and dark brown/black in colour. They have black legs and a large abdomen, and their fangs are not obvious. The females (up to 18 mm) are larger than the males (about 9 mm). The female spider never leaves her web unless forced to. Males, when ready to mate, go in search of females in their webs. The spiders mature during summertime and live for about 2 years.

Black house spiders are not aggressive and bite infrequently. Their bites can be quite painful with local swelling. Symptoms such as pain, nausea, vomiting, sweating and skin lesions have been recorded in a few cases.

Black house spiders are sometimes mistaken for funnelwebs because of the funnel in their web. However their webs are commonly found above ground level. True funnelwebs live in burrows in the ground.

Huntsman spider

Huntsman spiders are found living under rocks and loose bark, in crevices, on the ground and on foliage. They sometimes enter houses or cars. They do not build webs.

Huntsman spiders are very large, and can grow up to 15 cm across the legs. The females are bigger than the males. They are usually brown or grey in colour, and may have banded legs. The two front pairs of their legs are significantly longer than the back two.

The females produce a flat, oval white egg sac. They place it under cover and defend it for about 3 weeks. Even after the spiderlings emerge from the egg sac, their mother stays with them for several weeks. The lifespan of most Huntsman species is about 2 years or more.

Despite their size and appearance, huntsman spiders are relatively harmless and generally not aggressive. Their bites usually result only in local pain lasting for a short time, and swelling. However, huntsman spider bites have caused prolonged pain, inflammation, headache, vomiting and irregular pulse rate.

Trapdoor spiders

The common name trapdoor spider covers several families of spiders. In urban areas, trapdoor spiders control many of the garden pests. Since they are not considered to be dangerous to humans, it is best just to leave them alone.

The Melbourne trapdoor spider is common in our backyards. It is a ground dweller and builds burrows that have no trapdoor. They can be distinguished from funnelweb burrows by the absence of silk triplines around the entrance.

The Melbourne trapdoor spiders are robust, 15–35 mm in body length, light brown to dark brown in colour, and covered in fine hairs. Females are larger than males. These spiders tend to be quite timid.

The female lays her eggs in her burrow. Trapdoor spiders have a long life span (5–20 years) and take several years to reach maturity. Once mature, the males leave their burrows to search for a mate. The females stay in or near their burrows.

Trapdoor spiders are often mistaken for funnelwebs, but their bites are not dangerous. Due to the size of their fangs, the bite can be deep and painful with local swelling.

Wolf spiders

Wolf spiders are found throughout Australia in habitats ranging from dry inland to wet coastal areas. This distribution is aided by their ability to disperse on air currents as spiderlings.

They live on the ground in leaf litter or burrows, and are often found in lawns and gardens. They do not build webs and are often active during the day.

There are many species of wolf spider, ranging in size from about 10 mm to 80 mm. Their body colours are typically brown to greyish brown, with various patterns.

Wolf spiders have a distinctive eye pattern of two large eyes at the front with four small eyes in a line beneath them. The other two eyes are set back on the sides of the front segment, or cephalothorax.

The female wolf spider constructs an egg sac shaped like a ball, which she carries around attached to her spinnerets at the end of her abdomen. When the spiderlings emerge from the egg sac, they are carried around on her back until they are ready to disperse. Wolf spiders live for up to 2 years.

Wolf spiders are not aggressive, but can run very fast when disturbed. Symptoms of their bite are usually minor, such as local pain or itchiness. Less commonly, they have caused swelling, dizziness, nausea and a rapid pulse.

Daddy longlegs spider

Daddy longlegs is a common name used for a group of spiders, but it is also used for a different group of arachnids called harvestmen. Unlike spiders, harvestmen bodies do not have a 'waist' and do not produce silk. Daddy longlegs spiders are often found inside houses whereas harvestmen are not.

Daddy longlegs spiders are commonly found in dark areas. They build tangle webs and eat small insects and other spiders. They are pale brown to cream with long slender legs and relatively small bodies.

Females can grow up to 20 mm and are slightly larger than males, which can grow up to 16 mm.

Daddy longlegs spiders are harmless. The bite causes only a local reaction, if any.

Spider bite first aid

Those at greatest risk from a spider bite are the very young or elderly, and those with pre-existing cardiovascular disease.

If a funnelweb spider bite is suspected, it should always be treated quickly by applying a pressure bandage and immobilising the victim.

For redback bites, do not apply pressure – this often worsens the pain. For other spider bites, the area should be washed with soap and water, and a cold pack applied if the bite is painful.

For most spider bites, no other first aid is necessary. However, seek medical attention for any suspected funnelweb or redback spider bite, and for any other bite if symptoms develop or persist. If possible, catch the spider to help correctly identify it.

Spider pest control

Simple measures can be used to limit the number of spiders entering the house. Flyscreens can be fitted to windows, and weather strips or draft excluders will block their entry under doors. Trees and bushes planted away from the house will discourage spiders from making burrows close to, and wandering into, the house.

It is important to check clothes that have been left on the floor for spiders. You should wear shoes in the garden. While gardening, wear long trousers and thick gloves.

Insecticide spraying is not recommended for ground-dwelling spiders as it may make them more active and they may wander into the house. Boiling water may be poured down individual burrows.

Spiders are also known to fall into swimming pools and may survive submerged for a number of hours. People should be taught to respect spiders, rather than be frightened of them. Though many of them are harmless, it is still best not to touch them.

If spiders are controlled using chemicals, ensure that the pesticide is suitable for a domestic situation and appropriate for spiders. This information is on the label of the product.

Acknowledgements

The department would like to acknowledge the assistance and advice from Catriona McPhee.

Images reproduced courtesy of the Australian Museum and Museum Victoria.