A spider bite or some bite from an unidentified arthropod, a group of animals that includes both spiders and insects, is quite often identified by a physician as the bite of a brown recluse spider. In 1994, over 25% of the reported spider bites in the Pacific Northwest were reported as brown recluse bites.

Dr. Roger Akreetal, in an article titled The Great Spider Whodunit (Pest Control Technology 1994; vol 22 pages 44-50) stated that the most probable culprit of the “brown recluse” bites in the Pacific Northwest was the aggressive house spider, also called the hobo spider. Washington State University studies of numerous “brown recluse” bites never found brown recluse spiders, but did find hobo spiders in most cases.

I have examined over 70 specimens of spiders from customers in and around Bend who thought they had brown recluse spiders. Not one of these has been a brown recluse. I am aware of only one documented brown recluse spider specimen positively identified in the Pacific Northwest. That one was found in Spokane Washington in 1995.

Hobo spiders are the documented biters here in the Northwest.

So why are there so many “brown recluse” spider bites?

The answer can be found in the diagnostic references used by physicians to identify the probable cause of an arthropod bite. Most of these references list only two choices for physicians, either the black widow or the brown recluse spider. Only the most recently published books contain a mention of the hobo spider.

Necrotic arachnidism, which is the medical term for a bite thought to have been inflicted by a spider, usually begins with a localized reaction around the bite site. This reaction gets worse over time. Eventually, the tissue begins to deteriorate in the area and nervous-system related symptoms begin to appear.

So if you have a bite, from an unidentified (think reclusive) animal, and the symptoms include localized tissue deterioration and ulceration– then you have a brown recluse spider bite.

In reality, there are many animals other than the brown recluse spider that can cause these symptoms. I have been involved in bite investigations where other spiders, ticks and even some insects were identified as the probable cause for a bite that a physician had called a brown recluse bite. A person who is allergic to the secretions of a certain insect species could exhibit symptoms similar to a brown recluse bite if she/he was bitten by that species. The choices are certainly too numerous to list in diagnostic manuals.

The bottomline is that the brown recluse spider has yet to become established in the Pacific Northwest. Remember that the first step of any pest control operation should be the proper identification of the target pest. No PCO in Oregon should be treating for brown recluse spiders unless they have a positively identified specimen.

Three good references about spiders and spider bites are:

1. The Oregon Health Division’s CD Summary 1995;14 (no.22), title: Along Came A Spider Causing Necrotic Ulceration.
2. The Washington State University Cooperative Extension’s publication no. EB1548, title: Spiders. This brochure has excellent color photographs of spiders, bites etc. This publication is available through the Oregon State Cooperative Extension offices.
3. NPCA’s technical release dated 7/96, title: Necrotic Arachnidism- Pacific Northwest 1988-1996, available to members through the NPCA office.