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NPS Arrowhead National Park Service
US Department of the Interior
Office of Public Health 1201 Eye Street, NW
Room 1131
Washington, DC 20005

Phone: 202-513-7215
Fax: 202-371-1349
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Office of Public Health - Hobo Spiders Factsheet
Points Of Contact
(202) 513-7217
Assistant to Director for Science
(202) 513-7097
(505) 248-7806
Assistant to Director for Field Operations
(202) 513-7056
National Capitol Region
Northeast Region
(215) 597-5371
Southeast Region
(404) 507-5730
Mid-West Region
(402) 661-1718
Intermountain Region
(505) 988-6040
Pacific West Region
(510) 817-1375
Alaska Region
(206) 220-4270

How to identify a Hobo Spider?
There are three main types of Hobo spiders; Tegenaria agrestis, T. gigantic, and T. domestica. These spiders, also referred to as the Aggressive House Spider, have been suspected of living in the United States as early as the 1920's and 1930's. They are brown and the adults measure roughly 10-15 mm (0.4 - 0.6 inches) in body length and 15 to 45 mm (0.6 - 1.8 inches) in leg span. Their legs show no distinct rings and have short hairs. Their abdomens have several chevron shaped markings. Males are distinctively different from females in that they have two large palpi (mouth parts) that look like boxing gloves. These palpi are often mistaken for fangs or venom sacs, but they are in fact the male genitalia. The females also have these palpi, but the ends are not enlarged as they are in the males. Females tend to have a larger and rounder abdomen when compared to males. The Hobo spider has a distinctive web that is horizontal and flat with a funnel at one end. These funnel shaped webs are often attached to an object in the yard, by the foundation of structures, or anything that remains stationary near the ground. The spiders rarely climb vertical surfaces and are uncommon above basements or ground level.

Male Hobo Spider
Male Hobo Spider
Female Hobo Spider
Female Hobo Spider

These species were originally from Europe. It is believed that they were transported to the US via shipping lanes and ended up in Seattle, WA in the late 1920s. They have since expanded slowly throughout the Northwestern US and Western Canada. Their bites have often been confused with the brown recluse; therefore, public awareness of the hobo spider is low.

Why are Hobo Spiders a problem?
There have been about 175 reported bites from the Hobo spider. Although the bite of the hobo spider usually is initially painless, the bite of the hobo spider can be serious. About 50% of Hobo spider bites are "dry", meaning that no venom is injected and nothing happens to the victim. Typically when the venom is injected, the victim will experience an immediate redness, which develops around the bite then may begin to disappear within a few hours. The most commonly reported symptom is severe headache. Other symptoms can include nausea, weakness, fatigue, temporary memory loss, and vision impairment.

Very often for the first 24 hours it may appear no worse then a mosquito bite, then it appears to blister in the center. Within 24-36 hours the blister breaks open, leaving an open, oozing ulceration. Lesions generally heal within 45 days, but can result in a permanent scar, and healing can require up to 3 years if the bite occurred in fatty tissue.

What do I do if bitten?
When bitten by a spider, always try to capture the spider for identification. The specimen should be identified by an entomologist, cooperative extension agent, or similarly trained person. In the case of a hobo spider, not only is the species important, but the sex and age of the spider are equally important to predict severity of potential poisoning and assist the physician in planning a course of treatment. If you suspect a hobo spider or other venomous species has bitten you, see a doctor immediately. A survey should also be conducted at the site and appropriate control measures implemented (see below).

How are they controlled?
The NPS uses integrated pest management (IPM) as its method of choice for managing pests. IPM is a decision-making process that places particular emphasis on preventing pest problems.

According to experts, there are several measures that you can take to control Hobo spiders that are consistent with IPM practices. Wood, debris and vegetation should be removed from around the house or building foundation. Areas with dead wood are the natural nesting sites for these spiders. Inspect and replace damaged weatherstripping around doors and windows. The same should be done for door thresholds and door sweeps. Use yellow exterior lights outdoors that attract fewer insects, thereby reducing the food supply for spiders. Caulk cracks and crevices that could provide harborage for spiders. Ensure that crawl space vents are screened. Glue traps can be effective and are available from many sources. The spiders and their nests can also be vacuumed when found. The contents of the vacuum cleaner should be placed in a sealed plastic bag and disposed of to prevent the spider from crawling out of the vacuum. Exposure can be reduced by using gloves and other clothing that covers skin while working in areas that may be infested.

Insecticides are not usually needed to manage web building spiders, but if one seems to be indicated, confer with your region IPM coordinator to discuss this option.

References and additional information:
Necrotic Arachnidism - Pacific Northwest, 1988-1996, MMWR Weekly, May 31, 1996 / 45(21):433-6

Mallis, A. 1990. Handbook of Pest Control (7th ed.). Franzak and AMP; Foster Co. Cleveland, OH.

If you have any questions, please contact your nearest Regional Point of Contact, park sanitarian or call WASO Public Health for more information.

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