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Brown recluse spiders no threat in Idaho — unless they hitch a ride

Brown recluse spider
Brown recluse spider

Last week’s column on the benefits of spiders in the garden sparked a response I hadn’t anticipated: A half dozen people called or wrote to take me to task and/or demand a correction for failing to mention the danger of the brown recluse spider in Idaho.

I didn’t mention the brown recluse because experts say the spider does not live here — and, therefore, is not a threat to public health or safety.

“It is a persistent and widely held myth that we have them,” said Ian Robertson, professor in the Department of Biological Sciences at Boise State University.

Spider bites aren’t on the reportable disease list, so the state health department doesn’t have any data on how common spider bites are. I checked with local hospitals for data or anecdotal information.

St. Luke’s Regional Medical Center doesn’t track spider bites. A spokesman for Saint Al’s said there were two brown recluse bites reported last year at all their facilities.

“Instances of individuals seeking medical care following a confirmed brown recluse spider bite are uncommon, according to our database,” Josh Schlaich said.

Robertson and others believe Idahoans often confuse the hobo spider, also brown, with the brown recluse. One key difference between the brown recluse and other similar-looking spiders is their eyes: The brown recluse have six eyes, not eight, which are arranged in three sets of two.

“The bite of hobo spiders has been described as ‘mild recluse-like,’ which may help explain why people think we have brown recluse spiders in Idaho,” Robertson said.

Other info he shared: About half the bites of hobo spiders are dry bites, meaning they don’t contain any venom. In cases when venom is injected, most people have some localized swelling, soreness, and a hardening of tissue around the bite for several days. A small percentage of bites become more serious and may require medical attention.

Also notable: The hobo spider’s venom is not longer considered toxic. The U.S. Centers from Disease Control and Prevention removed it from the list of harmful spiders last year

The University of Idaho’s “Homeowner Guide to Spiders around the Home and Yard,” published in 2010, is emphatic about brown recluse spiders.

“In spite of what you may have read in a newspaper or even been told by your physician, the brown recluse spider DOES NOT OCCUR in Idaho.” (the all-caps emphasis is in the guide).

The spider does not live in the Northwest. Its range is primarily the central and southeastern U.S. The UI spider guide notes there was a case of a brown recluse found in Washington state in 1978 but was determined to have been transported in moving boxes by a family from Kansas.

spider map
Moeller, Katy - Boise
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Why not here? The climate of Idaho is inhospitable to the brown recluse

David W. Ragsdale, professor of entymology at Texas A & M University, said brown recluse spiders aren’t likely to survive outdoors in Idaho’s harsh winters because of the extensive time that foraging isn’t possible.

These spiders are, in fact, reclusive. They are nocturnal and gravitate to dark corners. That’s why it’s believed they sometimes end up in moving boxes headed for other states.

“The reality is that we are a very mobile society and move lots of arthropods around with us in our belongings. As a result, many species’ show up outside of what we think of as their typical range,” said Robert Puckett, assistant professor and extension entymologists at Texas A & M University.

The brown recluse spider doesn’t seek humans to bite — they typically bite when threatened, as when someone rolls over on top of them or steps on them, according to an extensive article by Wired titled “Why You Need Not Fear the Poor, Misunderstood Brown Recluse Spider.”

“It’s possible to live with the spiders and not get bitten,” the Wired article says. “Take the rather extreme example of a Kansas family that lived for six years in a house infested by 2,055 brown recluse spiders. Total bites: Zero.”

Katy Moeller: 208-377-6413, @KatyMoeller

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