CORVALLIS, Ore. – Hobo spiders are on the move this time of the year, when male spiders leave their webs in search of mates, according to Amy Dreves, entomologist at Oregon State University. After mating the males die.
Most of the time these big European spiders (members of the funnel-web spiders or funnel weavers) stay secluded in dark, dry places such as overgrown shrubs or the dark corners of a basement, wood pile or garage. But in the fall, the adult males begin to wander more openly and you may find them wandering into your house. They also are known as aggressive house spiders.
As they come out of hiding, you might see them scurrying across the kitchen floor or attempting to scale the slick walls of your bathtub. They are poor climbers but are among the fastest spiders known.
Adult hobo spiders are relatively large, dark brown and, including their long legs, about the size of a silver dollar. The males have two swollen appendages (actually the male genitalia) up front that look like a pair of boxing gloves.
Many Northwesterners share their homes and gardens with these and many other kinds of spiders. The hobo spider weaves a layered, flat web with a funnel-shaped lair at the back. There the spider resides and waits for its prey. The web is not sticky, like that of many other spiders, but trips up unsuspecting prey unable to navigate the layered surface.
The hobo will bite when tormented or pressed against your skin, however it is no more aggressive than other spiders, Dreves said.
"It does not bite without clear provocation and does not chase people down and attack them," she said. "Although the hobo is not aggressive, venom from its bite can cause local tissue blistering and lesion scarring damage, and may take months to heal."
Confirmed incidence of spider bites in humans, however, is very low. Many wounds that are more likely caused by other agents such as ticks or fleas are often misdiagnosed as spider bites, Dreves said.
Before you bring out the heavy artillery, Dreves offers some advice.
"It's important to know that there are fewer hobo spiders than beneficial spiders," she said. "In fact, the hobo's nearly look-alike cousins, the giant and domestic house spiders, are effective in keeping hobo spiders in check. It's easy to confuse their identification."
The hobo spider has an oblong, lightly hairy, tan-brown abdomen with broad reddish-brown zigzag stripes (chevron pattern) on top (dorsal abdomen). Underneath the spider, the sternum is marked with a pair of broad dark brown bands running lengthwise. The legs are unmarked and do not have rings around them. Both the domestic and gigantic spiders have three sets of dots instead of bands like the hobo. The domestic house spider is usually smaller in size and darker, and has rings on its legs. The gigantic is usually larger than the hobo.
Dreves recommends the following methods to reduce spider encounters:
- Wear gloves, pants and a long-sleeved shirt when handling firewood or stored boxes where spiders may have built funnel-shaped nests.
- Seal holes around doors, windows and outlets for plumbing and wiring where spiders can find entry into the house.
- Sweep webs from corners, rock walls, under eaves and around shrubs.
- Place simple cardboard sticky traps (without the use of insecticide sprays) along baseboards and bed frames where wandering spiders tend to move.
- Keep the premises free of debris such as boxes, papers, clothing and lumber. Keep wood piles a distance from the house.
- Keep vegetation mowed or trimmed to reduce contact with the structure.
For more information about spiders in Oregon, contact the OSU urban entomology web site. Emphasis is always on the least toxic approach to control.