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Hobo spider envenomation in Adult
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Hobo spider envenomation in Adult

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Contributors: Robert Norris MD, Joanne Feldman MD, MS
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Synopsis

The hobo spider, Tegenaria agrestis, is one of approximately 90 species of European house spiders. It is indigenous to Western Europe and is now found in the western United States and Canada after probably coming via ship to the Pacific Northwest in the 1930s. Since then, the hobo spider has migrated as far as Wyoming, Montana, and Colorado. In Europe, the hobo spider typically lives in fields, far from urban dwellings, because other spiders have filled the urban niche. However, in the United States, hobo spiders are often found in urban environments because of the lack of major competitors. The spider is moderately large, hairy, and brown with chevron-like strips on its dorsal abdomen. They have very poor vision, unable to see well beyond a foot or two away, and are poor climbers, so they are often found on the ground or in basements. Hobo spiders typically build funnel webs.

Hobo spiders have been called "aggressive house spiders" because they can move fast and have been noted to run toward individuals when disturbed. However, this is now believed to be a misinterpretation of their behavior. When disturbed, hobo spiders often remain still. If they run away, given their poor eyesight, they sometimes run toward an individual. Hobo spiders, however, will bite in defense when caught against the skin but usually will not bite without clear provocation. The toxicity of the venom depends on the spider's age and sex. Young adults and male hobo spiders have the most toxic venom.

Hobo spider envenomation is thought to cause local skin necrosis similar to brown recluse spider (Loxosceles reclusa) envenomation. However, in the medical literature, there is only one verified hobo spider bite that resulted in a necrotic lesion in a woman with a pre-existing medical condition known to cause ulcerations. The remainder of the literature implicating the hobo spider is based on anecdotes, a rabbit model, and circumstantial evidence (ie, hobo spiders found in the home of a person with a necrotic lesion). In Europe, hobo spider bites are considered medically insignificant, and research shows that the venom of European and American hobo spiders is identical. No study has identified a necrotoxic component in the venom.

Codes

ICD10CM:
T63.391A – Toxic effect of venom of other spider, accidental, initial encounter

SNOMEDCT:
217665000 – Poisoning due to venomous spider

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Last Updated: 06/14/2018
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Hobo spider envenomation in Adult
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Hobo spider envenomation : Skin ulcer, Spider bite, Tense vesicle, Painful skin lesion
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