Spiders Pest Note

Spiders - What are they?

Spiders commonly found in Canadian homes include house spiders, wolf spiders, cellar spiders, fishing spiders and, much more infrequently, black widow spiders. They are usually found in corners of rooms, closets, boxes, dark crevices, basements, garages, and gardens.

Household spiders

The spider has an unsegmented body with two main divisions and four pairs of walking legs. It also has organs for producing silk, which is used for making nests, webs to catch prey or cocoons for its eggs.

Spiders can have up to eight eyes. With so many eyes, it is surprising that most spiders are near-sighted. Most spiders prey on insects, many of them pests. Once the prey becomes tangled in the web, the spider immobilizes it by wrapping it in more silk and then injecting venom to paralyze it. Later, the spider injects a predigestive liquid and sucks out all the nutrients from its prey. Not all spiders are web spinners, and there are many types of spiders that use different strategies to catch their food. Most are nocturnal, shy, and avoid confrontation by running away. They will only bite if they feel threatened, for example being squeezed or held.

Wolf spiders

Wolf spiders are unusual because they do not build webs but rather hunt for their prey. These spiders can be as large as 3 cm in length and are dark brown in colour. The female spins a large white spherical egg sac that she attaches to her body and carries around until the eggs hatch, after which the newborn spiders stay on the mother's back for about a week. They are generally found on the ground in grasslands, woodland floors, beaches and gardens where they mostly feed on insects. In the fall, they look for warm places so they are more likely to enter our homes around that time.

Cellar spiders

These spiders have very long legs and build their webs in the corners of cellars or cool, damp basements. Cellar spiders are harmless and can be eliminated by removing the webs and reducing the humidity in that area of the house.

Cellar spiders have also been called daddy long-leg spiders and can be confused with another spider-like relative, commonly known as the harvestman or daddy long-legs. The harvestman does not have two distinct body parts like true spiders and it does not have silk-producing glands either, but it does have four pairs of long slender legs which make it look like a spider at first glance.

Household spiders and black widow spiders

The house and black widow spiders belong to the same family. The house spider is more commonly found within the house whereas the black widow spider is more likely to be found in dark crawl spaces, garages or outhouses. The house spider varies in colour from dirty white to nearly black with more or less visible markings on its body, and its first pair of legs is almost three times the length of its whole body. It builds webs in dark corners, under furniture and anywhere insects might be caught.

The black widow spider is shiny black with a distinctive red hourglass-shaped mark on the underside of the stomach. It spins a small, silk web close to the ground and is found in secluded places such as garages and sheds or under rocks or fallen trees when outside. It is not aggressive and prefers fleeing when disturbed, so it will bite only defensively. There are a few black widow species that can be found in Canada , mainly in the southern parts of the country, but they are not common. If you are concerned about the potential presence of black widow spiders, be careful when working around spider webs in secluded areas and wear protective gloves if needed.

Fishing spiders

Although fishing spiders look like wolf spiders, they have a different eye pattern. The adults can reach up to 7.5 cm in width. They are commonly found near cottages and waterfronts, especially around rocks near the shoreline. These spiders forage for their prey (insects, minnows, etc.). The females carry their eggs around in a spherical sac until ready to hatch. They then spin a web to surround their eggs and guard them until the spiderlings have all grown and dispersed. Unlike wolf spiders, which carry their egg sac behind the body, fishing spiders carry their egg sac under their head and front thorax (upper body).

What can they do?

Spiders are excellent pest control agents. Wolf spiders are especially helpful to farmers and gardeners because they prey on common crop pests like caterpillars, plant bugs and aphids. Spiders do not transmit any diseases. Although nearly all spiders have venom glands, they rarely bite humans, and only a few species, like the black widow spider, can have a dangerously venomous bite.

The degree of reaction to the black widow spider bite depends on the area of the body bitten, amount of venom injected and a person's sensitivity to the venom. Serious long-term complications or death are very rare. However, if bitten, remain calm, and immediately seek medical attention by contacting your doctor, hospital and/or poison control center. Apply an ice pack directly to the bite area to relieve swelling and pain.

How can I manage them?

Prevention

Keeping your house clean reduces the number of pests that are food sources for spiders. To prevent pests from entering your home, weather strip or caulk windows and doors and repair screens. When cleaning your garage or basement or working in your garden, it is a good idea to wear gloves to avoid exposing yourself to unexpected spider bites. Spiders are generally beneficial: a few spiders left in your basement and crawlspaces will help to capture earwigs and other insects.

Physical Control

• Sweep or vacuum baseboards and corners of rooms often to remove any food debris.
• Remove spider webs when spiders are not in them.
• Sweep behind washers and dryers often and rearrange furniture periodically to avoid spiders spinning webs in the same location.
• Keep clothing, shoes and blankets off the floor so that spiders do not hide in them during the day.
• If there is a spider near a door or window, chase it outside with a soft brush.
• You can also trap live spiders with a glass jar and a piece of stiff paper and then release them outdoors.
• If needed, they can be eliminated by using a fly swatter, rolled-up paper or magazine.
• Use yellow light bulbs outdoors to attract fewer insects, thereby discouraging spiders from spinning webs near your house.
• If you have an outhouse at your cottage, always check to make sure there are no spiders underneath the rim of the seat. Make sure that the outhouse is clean, the door is weather stripped and closes tightly, and all openings are screened properly.

Products

If the infestation of your house or garden is severe enough to warrant the use of pesticides, products containing the following chemicals are registered for controlling most common spiders: pyrethrin, permethrin and d-trans allethrin.

These products can be bought in hardware stores and garden centres. They can be applied around the exterior surfaces of window and door frames to prevent entry. There are also products that can be sprayed or painted on interior window and door frames, baseboards, floors, floor coverings, underneath furniture and in closets and crevices. Complete removal of spiders using chemicals is not recommended because spiders are natural and efficient pest control agents.