Males and immatures may be striped white or yellow. The adult female is 1.5 inches in diameter, including legs, and is jet black with red markings on the underside of her abdomen. Black widows can be very abundant in southwest Oregon. They may also be found west of the Cascades, especially on dry, open, south-facing slopes. Many believe black widows are found only east of the Cascade Mountains. Black widows may be found in houses, under furniture, in dark corners, and amid stored items. Occurs in the PNW generally in dry, undisturbed areas such as firewood piles, old lumber, dry crawl spaces, bales of hay, etc. The following discussion will help differentiate these spiders: The only known cases of this spider have been linked to people moving into the PNW from areas of known infestation. While the bite of the hobo spider is similar (see below), the brown recluse spider does not naturally occur in the PNW. Many spider bites reported in the PNW are attributed, unfortunately, to a spider that does not even live here, namely the brown recluse spider. A fourth spider, the hobo spider (or aggressive house spider), has long been blamed for spider bites but has now been exonerated: there is no scientific evidence that it produces necrotic bites. These are found frequently in houses, but few bites from these spiders in the PNW have been documented.
The other spiders of concern are two species of sac spiders in the genus Cheiracanthium. The black widow spider commonly occurs in association with humans and presents a real danger of poisonous bites. Only three spiders of medical importance live in the PNW. While all spiders use venom to subdue their prey (hence, all spiders are "venomous"), the bites of most spiders are often only mildly irritating. Pest description and damage There is much confusion regarding poisonous spiders in the Pacific Northwest, even among the medical community.
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