OHSU

Oregon Poison Center Still Searching for Biting Spiders

03/25/09  Portland, Ore.

Researchers aim to determine which Northwest spiders bite

The Oregon Poison Center at Oregon Health & Science University has been collecting spiders suspected of biting people. Researchers are hoping to determine which spiders in the Pacific Northwest bite, which may cause skin ulcers, and, specifically, whether the much-maligned hobo spider does either.

Eighteen months into the study, researchers have found 23 patients who have witnessed a spider bite them and have sent in the spider for identification. Spiders identified included funnel weaver spiders, cross spiders, yellow sac spiders, a Mygalomorph spider and two spiders with no common name (one Callobius species and one Araneus species). Only one spider identified was in the “hobo spider” family, but investigators were unable to determine if it was indeed a hobo or a closely related species.

Spider bites seem to be common in the Pacific Northwest. However, this is the first study to research which types of spiders are causing the bites and what effects they cause. One particular spider, the Northwest native hobo spider, has been implicated as a source of ulcers and skin infections for many years. Its venom has been demonstrated to cause tissue death when injected into the skin of animals, but there is debate about whether the spider ever bites or is even capable of biting humans.

Researchers are interested in clarifying the types of spiders that bite because much of the previous data linking spider bites to clinical effects, such as skin ulcers, has been based on circumstantial evidence. In some cases, people would see a skin ulcer or skin infection and automatically attribute the lesion to a spider despite never having seen one.

“We are concerned that people will mistakenly ascribe serious medical illnesses to spider bites,” said Robert Hendrickson, M.D., co-study investigator, medical toxicologist and associate professor of emergency medicine in the OHSU School of Medicine. “Several cases of skin cancer, cutaneous anthrax, Lyme disease, and skin abscesses have been initially assumed to be a spider bite and have led to delays in treatment.”

People who called the Oregon Poison Center with suspected spider bites were asked about the circumstances surrounding the bite (where they were bitten, whether the bite occurred indoors or outdoors), basic demographic information and any symptoms they were experiencing. Individuals were then contacted by phone within one week and again three weeks following the bite. Callers were sent a package in which to send the spiders to the poison center. All the spiders were identified by an arachnologist at University of California, Riverside.

Callers reported initial symptoms, including redness, pain, swelling and itching. The majority of symptoms resolved in three days, although one person had persistent symptoms for 12 weeks. None of the callers has developed skin ulcers or any other sign of serious infection.

Researchers hope to collect more spiders suspected of biting. They would like any Oregonians who see a spider bite them to collect the spider and call the Oregon Poison Center at 800-222-1222. The caller will be sent a postage-paid package in which to send the spider to the poison center.

“We understand not everyone will feel comfortable killing the spider, and we won’t pressure them to do so, but we would still like to hear about the spider bite,” said Nathanael McKeown, D.O., study co-investigator, medical toxicologist and assistant professor in emergency medicine in the OHSU School of Medicine.