The Hobo Spider
Common Name: Hobo Spiders Scientific Name: Tegenaria Agrestis (Walckenaer) Class/Order/Family: Arachnida/Araneae/Therididae Metamorphosis: Simple
INTRODUCTION
The common name comes from this spider's method of very rapidly expanding its distribution by hitching rides with humans along major highways in the Pacific Northwest; it was formerly known as the aggressive house spider. Their webs are a nuisance but their bite is of medical importance to both humans and pets because it may result in a slow-healing lesion. This species was introduced from Europe and first found in Seattle in the 1930's, and is currently common in the Pacific Northwest (Idaho, Montana, Oregon, Utah, Washington) and British Columbia. The hobo spider appears to be rapidly expanding its range, displacing many native spiders as it spreads.
RECOGNITION
Adult female body length about 7/16-5/8" (1 1-1 6 mm) including oblong abdomen, male body length about 5/16-7/16" (8-1 1 mm); total size including legs about 1-1 314" (40-50 mm) in diameter. Color variable with carapace (cephalothorax dorsum) light to medium brown, with dark stripe to either side of lighter midline stripe, dark stripe with lateral extensions in posterior half; abdomen with interrupted light midline stripe with about 5 light colored triangular shaped loops on each side bordered by a dark background but usually 1st I or 2 and last 2 or 3 loops incomplete, last 2 or 3 loops chevron-shaped (stripes meeting at angle medially; "army sergeant stripes") with enlarged ends, white on darker dorsal coloration gradually changes to dark blotches on a lighter background on sides and venter; sternum (venter central area between coxae) with light midline stripe and usually solid dark lateral stripe on each side; legs solid light brown, no bands. With 8 eyes in 2 transverse lineslrows, front row slightly curved forward and rear row almost straight. Cephalothorax, abdomen, and legs with plumose (featherlike) hairslsetae. Abdomen with longer posterior spinnerets extending beyond abdomen, visible from above. Tarsi with 3 claws each.
SIMILAR GROUPS
- Domestic (Tegenaria domestics) and giant (Teganaria gigantea) house spiders with posterior line of 4 eyes curved rearward and sternum with lateral dark stripes containing 3 pairs of light circular marks each; in addition T. domestics has banded/ringed/annulated legs.
- Grass spiders (Agelenopsis spp.; Agelenidae) with carapace (cephalothorax dorsum) yellowish to dark brown with 2 dark longitudinal stripes, abdomen yellowish gray to dark brown and patterned, and legs banded/ringed/annulated.
BIOLOGY
Hobo spiders have a 2-year life cycle. Mating occurs in the autumn. In mid- September to October, the female spins a hemispherical silken egg sac into which she deposits her eggs. In the spring, spiderlings molt once within the sac before emerging as 2nd instars in early June. They molt a second time about one week after emergence and continue moiling monthly for about 12-15 molts. They spend the second winter as immatures. Males mature the second summer from June through September, and females mature from late June to September. Mating occurs, and most males die before October. Females lay eggs in sacs until cold prohibits activity and usually die from late autumn to early spring. However, some females may live 3 or more years.
The bite of these spiders typically produces a necrotic lesion similar to that caused by brown recluse spiders, Loxosceles spp. The initial bite produces a very slight prickling sensation. Within 3 minutes or less, a small, insensitive, hard area appears which is surrounded by an expanding reddened area of 2-6" (51-153 mm) in diameter. Within 15- 35 minutes the area blisters. About 24 hours later the blister usually breaks, and the wound oozes serum. The cratered ulcer crusts over to form a scab. Tissues beneath the scab may die and slough away; severe bites may require surgery to close. The fully developed lesion may be up to 1/2-1" (12-25+ mm) or more in diameter. It may take several months to heal and often leaves a permanent scar.
Systemic illness occasionally occurs. The most common symptom is a severe headache, sometimes within 30 minutes but usually within 10 hours, which does not respond to aspirin and may last for 2-7 days. The headache may be accompanied by nausea, weakness, joint pain, fatigue, and vision impairment, symptoms commonly associated with migraine headaches. A low blood platelet count (<150,000) may occur at about 36 hours which recovers in about 7-10 days.
Only a few dozen bites are attributed to this spider for several reasons. Rarely is the culprit caught in the act, captured, and/or properly identified. It is common for people to use home remedies and never see a physician unless severe conditions develop. Many physicians in the Pacific Northwest attribute necrotic lesions to the brown recluse spider, which does not occur in these states, because of a lack of knowledge that the hobo spider is a problem and of brown recluse distribution. Fortunately, treatment is similar and a physician should consult brown recluse bite treatment resources for treating hobo spider bites. Antibiotics do nothing to alleviate the effects of the venom, although they are often prescribed. At least a couple of deaths may have resulted from hobo spider bites.
HABITS
Hobo spiders may be found in almost any habitat containing holes, cracks, or crevices which can support tunnel formation. Since they are poor climbers, they are rarely found above ground level. They frequent dark, moist areas, and are most often found in basements, window wells, and crawl spaces. Common web sites include rock retaining walls, soil and concrete cracks, the junction of foundations and tall grass, firewood and lumber piles, landscape timbers, stones and rocks partially raised above the ground, etc.
These spiders build funnel webs opening at both ends with one end expanding outward into a broad, sightly curved sheet. Vibrations from struggling prey (usually insects) ensnared on this sheet alert the spider which runs out of the funnel, bites the prey, and quickly carries it into the funnel. An escape tunnel is commonly built in the back of the web which leads to a deep crack or other protected area.
From late June to October, males extensively wander about seeking a female mate. It is not uncommon for several roving males to enter the ground level of a structure each day. lmmatures wander about in the spring in search of a web site. This wandering tends to bring them into contact with humans. They can be seen moving on floors or get trapped in various objects such as buckets, sinks, bath tubs, open jars, and children's toys. Immatures can be found year-round in basements and garages behind stored items, behind furniture, under raised baseboard heaters, in closets, etc.