Aggressive House Spider

AGGRESSIVE HOUSE SPIDER The aggressive house spider, Tegenaria agrestis, is also called the funnel-web or hobo spider. These spiders build funnel webs in dark, moist areas, often in basements, and sit in the mouth of the funnel waiting for prey. The funnel opens at both ends and the web expands outward into a broad, slightly curved sheet. When prey, usually an insect, becomes entangled in the web, vibrations from its struggle alert the spider, which scurries out to bite the prey. The subdued prey is then carried into the funnel. The hobo spider is one of three very similar spiders found in homes in the Pacific Northwest. It is often found in basements and in window wells of houses. It rarely climbs vertical surfaces and is usually found on the ground or lower floors. It is called the aggressive house spider because it bites when cornered or threatened. These are fairly large, swift running spiders. Mature adults range from ¾ to 1 inch in diameter, not including the legs. Mature males and females are abundant from mid-summer (July) through fall. During this period males tend to wander relatively long distances in search of females. Eggs are laid into a spherical silken sac spun by the female, usually in September or October. The sac is then placed within or adjacent to the funnel, usually on the underside of a rock or other object. This sac is usually covered with a thin layer of soil, wood chips, or other debris. The debris-coated sac is then often covered with another layer of silk. Eggs hatch the following spring. Research on the bites of the aggressive house spiders determined that the venom produces skin injuries or lesions similar to those produced by the brown recluse. In Washington, Oregon and Idaho ulcerating lesions of this type are probably due to bites by the aggressive house spider. Bites commonly occur when a spider is squeezed against the body when a homeowner picks up a firewood log with a spider on it or when a spider is located in an article of clothing and is squeezed when the clothing is put on. The initial bite is not painful. It has been described as producing a very slight prickling sensation. However, a small, insensitive, hard area appears within 30 minutes or less, and is surrounded by an expanding reddened area 2-6 inches in diameter. Within 15 to 35 hours the area blisters. About 24 hours later the blisters usually break and the wound oozes serum. A cratered ulcer crusts over to form a scab. Tissues beneath the scab may die and slough away. In some cases the loss of tissue may become so severe that surgical repair is needed. The fully developed lesion can vary from about ½ to 1 inch or more in diameter. Lesions may take several months to heal, and frequently leave a permanent scar. Systemic illness may or may not accompany the bite. The most common symptom is a severe headache, sometimes occurring within 30 minutes, usually within 10 hours, which does not respond to aspirin. The headache may persist for 2 to 7 days, and is sometimes accompanied by nausea, weakness, tiredness, temporary loss of memory, and vision impairment. The symptoms are similar to those experienced with migraine headaches. Bites of the aggressive house spider have not caused a recorded death. In Europe, their area of origin, there are few records of bites by these spiders causing medical problems. However, a person bitten by one of these spiders should seek immediate medical treatment. Control Most spider problems can be solved without the use of chemicals. The first and best control is exclusion. Inspect door and window casings in the house for closeness of fit. Repair holes large enough to admit spiders. Other areas to inspect include entry points of water pipes and electrical lines. Caulk any cracks and other small openings. Screen vent openings. Before bringing firewood into your home inspect it for spiders or their egg sacs. In addition, keep woodpiles and other debris away from the house. Second, vacuum, vacuum, vacuum! If possible, use a vacuum with a hose that will readily remove all spiders and webs from corners and nooks. Removing the funnel web eliminates the spider’s habitat. Crush spiders by stepping on them, or capture them with your vacuum. Dispose of the vacuum bag immediately after capture so spiders will not escape. If spiders are persistent, use sticky traps sold at nurseries and garden stores. These are safe and have been demonstrated to be effective. Use of chemicals inside the home is not recommended and seldom necessary.