Region’s Nasty Hobo Spiders Hit Their Toxic Peak This Week

They move quickly and their bites are toxic. Hobo spiders are back.

This is the peak week for the dangerous pest, because it’s mating time.

The spider is native to Idaho, Oregon and Washington, and for years, its bite was thought to be that of the brown recluse spider.

But Darwin Vest, research toxicologist at Idaho Falls, said the closest brown recluse is at St. George in southern Utah.

Vest pioneered research into the hobo spider beginning in 1983 and he was the one who discovered and named the spider as the culprit in many toxic spider bites in Idaho.

Hobo spider bites began appearing in eastern Idaho in the 1960s and 1970s.

Vest said the number of spiders has been stable for the last 10 years. He doesn’t see an increase, but rather a migration into agricultural fields.

Rather than spraying for the pest, he recommends using a sticky trap. The problem with spraying, Vest says, is that it also kills the natural enemies of the spider.

Hobo spiders like to live in basements or crawl spaces. They can climb walls but usually don’t. The spiders weave a funnel web that isn’t sticky but attracts insects.

The funnel-like webs usually are found in rock walls or in wood piles - any place they can build and back into a dark area, according to Bingham County Extension Agent Brian Finnigan.

Finnigan said hobo spiders are killing the more common house spiders and taking over their webs. It does have a few natural enemies.

In Europe, the giant house spider has kept hobo spiders from entering homes. That insect was introduced on the West Coast, but doesn’t like the dry desert areas of Idaho, so it hasn’t migrated here.

That spider is three times larger than the hobo spider, and probably would be no more welcome in homes than the hobo, but its bite is not toxic to humans.

Vest said 45 percent of the people suffering from a hobo spider bite suffer severe headaches and nausea, from a very complex type of poison.

Most people don’t know they’ve been bitten because the initial bite is painless. A bump shows up in about a half hour and symptoms become worse, including an open sore that can take months to heal.

So far this summer, Bannock Regional Medical Center in Pocatello has treated about 20 spider bites, about the same as last year.