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Hobo Spider (a.k.a. Aggresive House Spider)
The Aggressive House Spider, Tegenaria agrestis, is called such because some specimens bite with little provocation and because they move forward to attack when cornered or threatened. More importantly, the name serves to alert individuals to the fact that this spider is potentially dangerous and should be approached with caution.
BITE: Investigations of aggressive house spider bites show that the venom produces skin injuries, or lesions, similar to those produced by the brown recluse (which is NOT found in this area!).Therefore, ulcerated lesions of this type are probably due to bites by the aggressive house spider. Males are somewhat more venomous than females.
Bites commonly occur when firewood is picked up because spiders love to build their webs in places that are dark and secluded. Bites can also occur when putting on an article of clothing that has been left on the floor, because this is another desired spider habitat. Although these spiders are not known climbers, bites do occur in the bed as they can crawl up any bedding that is floor length. They also have been found in sinks, bathtubs, shoes, and childrens’ toys. The initial bite is not painful and has been described as producing a very slight prick sensation. However, a small, insensitive, hard area appears within 30 minutes or less, and is surrounded by an expanding reddened area of 5 cm to 15 cm in diameter (2 inches to 6 inches). Within 15 hours 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 inch 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 headaches that does not respond to aspirin. The headache may persist for two days to seven days, and sometimes is accompanied by nausea, weakness, tiredness, temporary loss of memory, and vision impair-ment. Bites by T. agrestis have not caused a death. However, a person bitten by one of these spiders should seek immediate medical attention.
HABITAT: A member of the family Agelenidae, this spider is commonly called the funnel-web spider as it builds funnel webs within practically any habitat that has holes, cracks or crevasses to support tunnel formation. The funnel is open at both ends, and the web expands outward into a broad, slightly-curved sheet.; When prey, usually insects, becomes entangled in the web, vibrations from its struggle alert the spider which dashes out to bite.
These spiders are poor climbers so are rarely seen above ground level. But they are one of the most common spiders found in houses; (basement, closets, behind furniture, on window sills), and in garages.
Curently T. agrestis has not been found east of Billings (Yellowstone) or Havre (Hill) counties.
HISTORY: Although this spider was first reported in Seattle in 1930, it did not become common in the Pacific Northwest until the 1960's. In Europe, members of the genus Tegenariaare often called house spider since they are common inhabitants of houses and; adjacent vegetation. Only a single species of Tegenaria, (T. chicicahuae), is native to the United States, occurring in caves and other dark places in Arizona and New Mexico.
The other six species of Tegenaria found in the U.S. are of European origin. They were probably introduced to this country very early through commerce. Three species occur in the Pacific Northwest.
Tegenaria domestica, the domestic house spider, is common in both the Northeast and the Northwest, while Tegenaria gigantea, the giant house spider, has been collected in Seattle and near Pullman, as well as in Vancouver and in Winnipeg, Canada.; Neither of these two species are known to cause serious bite reactions in humans.
DESCRIPTION: Tegenaria agrestis is a relatively large, swift-running spider. Mature adults range from 4cm to 5cm diameter (1 inch to 1¾ inches) including legs (Figure 3). As with most spiders, males can be identified readily by the expanded, swollen tips of their palps.
Sexually-mature males and females are abundant from late June through fall. During this period, males tend to wander long distances in search of females. Eggs are laid into a spherical silken sack 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. The sac is then covered with a thin layer of soil, wood chips, or other debris, including prey. The debris-coated sac is then often covered with another layer of silk. Eggs hatch the following spring.
Most Tegenaria molt about ten times over a span of two years before reaching sexual maturity.; Immatures are commonly found wandering in the spring searching for webs.
CONTROLS: All spiders are beneficial! They catch and eat nuisance insects such as flies, ants, aphids, plant-feeding bugs, cock-roaches, small grasshoppers and crickets, thrips, leafhoppers, whiteflies and mosquitos. They are also excellent indicators of carpenter ant infestations as their webs are commonly near the house where ants forage, and become trapped. While elimination of some spiders is acceptable when they are an annoyance, wholesale elimination is ecologically unsound and results in more nuisance pests.
Cultural
The best method of control for Tegenaria is that of prevention. Prime habitat, such as tall or matted grass next to the house or fence, should be cut and/or removed and replaced with at least a 12-inch gravel edging. Cracks and deep cavities in rock walls should be filled with soil or cement. Lumber and firewood piles should be modified to eliminate cavities. Holes in the walls of the house for pipes or electrical lines should be sealed, as should the holes resulting from broken windows or screens, and ill-fitting doors. Always inspect fire-wood for spiders and their egg sacs.
Once a spider is in the house, the best elimi-nation is to crush the spider with a news-paper or flyswatter. Spiders found in sinks or bathtubs can be killed with hot water. Another good method for elimination is to vacuum the spiders and then immediately dispose of the dust bag by sealing it inside a plastic bag so the spider cannot crawl out.
Traps
No traps have been constructed for Tegenaria spp. but some people have had success using a small box (about 2 inches by 8 inches) with two ends open and applying Tangletrap (or some other sticky material) to the bottom and sides. Traps should be placed in basements, crawl spaces, along walls or passage ways from the outdoors where the spiders are most apt to be. Place the traps in June and change every two months while spiders are visible. The only problem is that females rarely wander. Therefore, only males in search of mates and immatures in search of a web site in the spring will be caught.
Insecticides
If spiders are numerous and constantly entering the house, insecticides labeled for spiders are available on the market. How-ever, according to research, insecticides are not particularly effective on the Aggressive House Spider. For example, in one study, only 23% of spiders exposed to Dursban were killed. Labeled materials include sprays containing Dursban (chlorpyyrifos microencapsulated - ME) and Knoxs-Out (encapsulated diazinon). Do not exceed the recommended dosage given on the label. These materials are probably best applied only along baseboards, door casements, and corners, and then only where spiders are present. But spraying the house foundation perimeter BEFORE spiders begin to move indoors is the preferred control option.
Firewood Management
Bora Care (sodium octaborate), Ortho Diazinon Insect Spray, or Green Thumb Termite Killer (chlorpyrifos) are products currently registered for use on firewood; however, do not breathe smoke from treated wood! The best protection is to wear gloves and a heavy, long-sleeved shirt when hand-ling firewood or debris that may harbor spiders. Adults spiders in an outdoor wood-pile should die over the cold winter months.
Written by Will Lanier
INFORMATION TAKEN FROM:
Biology & Medical Importance of the Aggressive House Spider in the PNW Roger B. Acre and Elizabeth Myhre Dept. of Entomology, WSU, Pullman WA.
EB1548 “Insect Answers”, WSU Cooperative Extension
1999 Pacific Northwest Insect Control Manual
MSU Pest Recommendation Database
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