Spiders

Spiders have an ominous, but often undeserved reputation. Though most spiders are venomous and considered predators, of the thousands of species found in Canada, few are actually considered a health threat. In fact, spiders are actually helpful in controlling other pests in the home or garden since they feed on other insects and spiders. They generally bite and inject venom into their prey. Spiders, however, rarely bite humans.

Although spiders are often unpopular, the venom of most species is not very toxic to humans, usually resulting in no more than a slight swelling, inflammation, or itching sensation. Most spiders’ fangs are too small or weak to puncture human skin. Spiders usually will not attempt to bite unless accidentally trapped against the skin or grasped, although some species actively guard their egg sacs or young.

Two spiders that can be a health risk are the brown recluse and black widow.

One of the most common misconceptions about spiders is that they are insects. Spiders are arachnids and are actually closely related to mites, ticks and scorpions. Spiders have two body parts (cephalothorax and abdomen), eight legs and usually six to eight eyes, while insects are classified by having three body parts (head, thorax and abdomen), six legs, and generally two compound eyes or up to three single eyes. The average life span of a spider is usually one to two years, but some can live five years and up to 20 years.

Life Cycle and Habits

Spiders lay eggs within a silken egg sac that is often ball-shaped and either hidden in a web, affixed to a surface, or carried by the female. Spiders may produce several egg sacs, each containing up to several hundred eggs. A spider grows by shedding its skin (molting), usually four to twelve times before maturity. In many species, the mature male often wanders about in search of a mate. Some species of spiders may live for years, but most spiders only survive for one season.

All spiders produce silk, which is secreted as a liquid through the spinnerets and hardens on air contact. Spiders use silk for a variety of purposes, such as making egg sacs, capturing prey, holding prey, making shelters or retreats, and transferring sperm during mating. Also, spiderlings extrude silk threads that enable them to be transported by air currents, a process called “ballooning.”

Spiders are predators that typically feed on living prey. They produce venom that is poisonous to their normal prey of insects, mites, and other small arthropods. Venom is injected through the hollow fangs to immobilize the prey and begin the digestion process. Spiders can only ingest liquids, so they either inject or regurgitate digestive fluids into the prey. They then suck in the digested liquid food.

Spiders use a variety of tactics to capture prey. Some species are web builders that use webbing to ensnare their prey. Others are active hunters that actively search for their prey. Passive hunters are spiders that lay in wait for their prey rather than searching for it.

Control Measures

The simplest method of controlling spider infestation is to reduce the pest population (other insects) inside the home so they seek a more dependable food supply outside the home. Control of spiders is best achieved by following an integrated pest management (IPM) approach that involves multiple tactics, such as preventive measures, exclusion, sanitation, and chemicals applied to targeted sites. IPM requires a thorough inspection of the building to locate the pest and its harborages. An inspection should be done at night if the species is nocturnal.

An important first step is to correctly identify the spider, as this determines which management tactics to adopt that take into account specific biology and habits. For example, if the spider is a web builder, control efforts should target its web because that is where this spider spends most of its time. On the other hand, active hunters are spiders that move about widely, and some species are most likely to contact insecticide-treated surfaces at ground level.

Within each of the following categories, particular tactics may be more or less applicable, depending on the species of spider:

Preventing spider bites

Shake out clothing and shoes before getting dressed.
Inspect bedding and towels before use.
Wear gloves when handling firewood, lumber, and rocks (be sure to inspect the gloves for spiders before putting them on).
Remove bedskirts. Move the bed away from the wall.
Don’t store boxes and other items underneath beds.
Exercise care when handling cardboard boxes (some spiders may inhabit the space under folded cardboard flaps).

Exclusion

Install tight-fitting screens on windows and doors; also install weather stripping and door sweeps.
Seal or caulk cracks and crevices where spiders can enter the house.
Equip vents in soffits, foundations, and roof gables with tight-fitting screens.
Install yellow or sodium vapor light bulbs outdoors since these attract fewer insects for spiders to feed upon.
Many web-making spiders set up residence near lights that remain on at night. Locate such lights away from the house or turn them off when not needed.
Tape the edges of cardboard boxes to prevent spider entry.
Use plastic bags (sealed) to store loose items in the garage, basement, and attic.

Sanitation

Remove trash, old boxes, old clothing, wood piles, rock piles, and other unwanted items.
Eliminate clutter in closets, basements, attics, garages, and outbuildings.
Store items off the floor and away from walls in basements, crawl spaces, attics, garages, and outbuildings in order to reduce spider harborage sites.
Eliminate household pests (prey) such as flies, ants, and cockroaches that attract spiders.
Do not stack wood against the house.
Remove heavy vegetation and leaf litter around the foundation.
Wash spider webs off the outside of the house using a high-pressure hose.

Non-chemical control

Capture the spider and release it outdoors. An effective technique for capturing hunting spiders is to place a cup over the spider and then slide a piece of paper underneath to entrap it.
Dust and vacuum thoroughly to remove spiders, webs, and egg sacs (dispose of the vacuum bag in a container outdoors).
Outdoors, use a water hose or broom to regularly destroy any webs that are constructed on or around the house. Spiders often move elsewhere when their webs are regularly destroyed.
Use a rolled up newspaper or fly swatter to kill individual spiders.
Use sticky traps or glueboards to entangle spiders.
Eliminate or shield outdoor lights or bright indoor lights that attract the spiders’ insect food source.
Trim vegetation around the building foundation and remove debris to discourage insects and spiders from living next to a structure.
Seal openings and install screens and door sweeps to prevent spiders (as well as other unwanted pests) from moving indoors.

Insecticides

There are many labeled pesticides for spider control. Some are labeled for homeowner use, while others are labeled only for the licensed, certified pesticide applicator. If insecticides are used, read the label and follow the directions carefully. A pest professional is familiar with the safe use of insecticides and may be the best choice to safely control spiders. (Directory of Canadian pest professionals)

Individual exposed spiders can be killed with a nonresidual aerosol spray, but any egg sacs will be unaffected. It generally is best to use a vacuum cleaner so that the egg sac is removed from the premises.

For web builders, insecticide treatments should be applied so that the chemical contacts spiders in their webs. A nonrepellent insecticidal dust is useful to treat webs because the dust clings to the silk and is likely to be contacted by the spider. Residual dusts can be applied to voids and inaccessible areas where spiders may hide.

A wettable powder or microencapsulated “slow-release” formulation of a residual insecticide can be applied to corners, behind and under furniture, behind stored items, etc. to control active hunting spiders. This approach also is useful to prevent establishment of new spiders. Aerosol flushing agents such as pyrethrins, though ineffective by themselves in providing long-term control, can cause spiders to move about so that they contact treated surfaces.

Residual liquid sprays can be applied to the outside perimeter of the home (including under eaves, patios, and decks; behind window shutters), cracks and crevices of decorative molding, undisturbed corners, and other suspected spider harborages. Residual liquid sprays applied to the outside perimeter of the home are not very effective for species that display web-sitting behavior.

Black Widow

Brown Recluse

House Spider

Spider Identification photos

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Spider Bites In the Pacific Northwest There is much confusion regarding poisonous spiders found in the Pacific Northwest (PNW). This confusion extends, in many cases, even to the medical community. Only four spiders of medical importance occur in the PNW. Two of these, sac spiders in the genus Cheiracanthium, are rarely encountered. The other two, the aggressive house spider, or hobo spider, and black widow spider occur commonly in association with human activity and present a real danger in terms of bites. However, many insect/spider bites reported in the PNW are, unfortunately, attributed to a spider that does not even occur here, namely the brown recluse spider. While the bite of the aggressive house spider is similar (see below), the brown recluse spider does not naturally occur in the PNW. The only known cases of this spider have been linked to people moving into the PNW from areas of known distribution. The following characteristics should help to separate these spiders. The black widow spider (Latrodoctus sp.) occurs in the PNW generally in dry, undisturbed areas such as firewood piles, old lumber, dry crawl spaces, bales of hay, etc. The adult female is 1-1/2 inch in diameter, including legs, jet black with red markings on the underside of her abdomen. Males and immatures may be striped white or yellow. This spider is secretive, not aggressive, and rarely causes bite injuries. The venom is neurotoxic and may lead to systemic effects, sometimes even death. Aggressive house spider (Tegenaria agrestis) is common in the PNW in and around houses, barns and sheds. It is a member of the funnel-web spider group. This is a relatively large spider (body size, excluding legs 3/8" - 5/8"; 1" - 1-3/4" including legs) with long, hairy legs and chevron-shaped abdominal markings. The venom is necrotic, causing open, localized wounds that may be slow to heal. Males may be more venomous than females and become quite common in mid-summer through the fall during the mating season. Despite its aggressive nature, however, reported bites from this spider are relatively rare. There are several closely related species that look very similar but whose venom is not as toxic.

The two most common types of spiders that are considered health threats in Canada are
the black widow and brown recluse.

Brown Recluse
DESCRIPTION
The brown recluse spider (Loxosceles spp.) is a poisonous spider that is light brown in color. It is about 1/2 inch in length, has a violin-shaped marking on the thorax (mid-section) and is sometimes called a fiddleback spider due to the unique markings. While most spiders have 8 eyes, the brown recluse has 6 (3 pairs). The brown recluse spider received its name because of its color and reclusive behavior. These spiders make an irregular and sticky web that is used for shelter rather than for trapping insects.

BIOLOGY
There are seven species of brown recluse spider that are a health concern in the United States. Though active throughout the year, they often go unnoticed because of their reclusive habits. Adults may be found in dark, secluded indoor places that are dry, cluttered, undisturbed and contain a supply of insects for food. They are most commonly found behind baseboards, under tables and chairs, in the basement, crawlspace, attic, infesting cedar shake roofs, and in garages and sheds. Another common hiding place for a brown recluse is in garments that are left hanging undisturbed for some time and in the linens of beds that have been unoccupied for a long while. Bites often occur when the spider is trapped in shoes or clothing, rolled on while in bed, and encountered when cleaning storage areas.

The brown recluses venom is a cytotoxin that attacks the cells of flesh and produces necrosis or dead tissue in humans. Though fatalities from the venom are very rare, the reaction to the venom depends on the amount of and individual sensitivity to the toxin. The bite is not usually felt, but a stinging sensation may develop shortly after, followed by intense pain. The reaction, however, may not occur until an hour or more after the bite. The bitten area will first develop a small, white blister and enlarge to the size of a silver dollar as the venom attacks and kills the tissue in the affected area. Eventually, the affected tissue will die and leave a sunken, ulcerated sore. The healing process is slow, generally six to eight weeks. If bitten, call a physician or go to the emergency room immediately. If possible, exterminate the spider and take it along for identification purposes. Though no antitoxin is available, prompt medical treatment can prevent severe reaction and minimize the extent of damaged tissue and eventual scarring.

SOLUTION
To avoid getting bitten by the brown recluse, shake out unworn or stored shoes and clothes before wearing, check bed linens of unoccupied beds and wear leather gloves when working around potential habitats. Use caution around spider webs in basements and crawlspaces. If a brown recluse is encountered, contact a pest control professional.

Black Widow
DESCRIPTION
The female black widow spider (Latrodectus spp.) is a poisonous spider that has a somewhat round, shiny black abdomen with red markings that resemble an hourglass on the underside. The size of the body is approximately 1/2 inch wide and 1 1/2 to 1 3/8 inches long. Despite common opinion, the female rarely kills the male after mating.

BIOLOGY
Five different species of the black widow spider are prevalent in North America. They generally live under rocks and under fallen trees outside the home. In and around the house they are often found in firewood piles, basements and crawlspaces. They are also found in secluded places, such as garages and sheds. They feed on insects and other spiders that are trapped in their web. They are usually not aggressive spiders, but if handled or accidentally touched, they may bite.

The black widow’s venom is a neurotoxin that attacks the nervous system and may cause pain and serious illness in humans. Though the bite is not often felt, pain will develop immediately. Reactions to the black widow’s venom include increased body temperature and blood pressure, profuse sweating, dizziness, blurred vision, nausea, and pain and swelling around the bite. Antitoxin is available to combat the neurotoxin. If bitten, call a physician or go to an emergency room immediately. If possible, exterminate the spider and take it along for identification purposes. Bites are rarely fatal when promptly treated, however, small children are at greater risk.

SOLUTION
To avoid getting bitten by the black widow, wear leather gloves when working around potential habitats. Use caution around spider webs in basements and crawl spaces. If a black widow is encountered, contact a pest control professional.
The university of Arkansas has a good web page on Black Widow Souders

The House Spider is brown in color and its body is about 3/8-inch long. Its abdomen is spherically shaped, and is white to brown in color with several dark markings. Males are smaller than females, and their legs are orange in color. The female's legs are yellow. This spider is the most common type of comb-footed spider, a group that includes the black widow species. They are urban pests named after the comb-like row of bristles located on the tarsi of their fourth pair of legs. House spiders are common throughout the world, and their webs are most often found in corners, basements, crawlspaces, under furniture and around windows. The venom is necrotic, causing open, localized wounds that may be slow to heal but Despite its aggressive nature, reported bites from this spider are relatively rare.

Source: New Age encyclopedias, Truman's scientific guide to pest control operations ( Purdue University), Compton's ency. on CD, Random internet research.