Hobo Spiders in Idaho
The hobo spider, also mistakenly called the aggressive house spider, is a European species first detected in Idaho during the 1960s. It is now common statewide. Lone adult males are frequently seen running across basement and ground-level floors inside homes from mid-July to the first killing frost. Hobo spiders can be worrisome due to their appearance, darting behavior, and unearned reputation as a threat to human health.
Hobo spiders are large (1¾ inches in diameter with legs extended), tan gray, and marked with a series of five or six light-colored triangular loops on the upper surface of the abdomen (Figure 1). Legs are uniformly tan, so if you see alternating dark and light marks on the legs, it cannot be a hobo spider. Professional assistance may be needed to confirm identification.
Contrary to a common belief, hobo spiders cannot be identified by their “boxing-glove” appearance. Many species of adult males have enlarged pedipalps (appendages on each side of the mouth) that look like boxing gloves. Another harder-to-see feature is their eight equal-sized, dark eyes arranged in two rows across the face. If a spider has both large and small eyes, it cannot be a hobo spider.
Hobo spiders run with rapid, darting movements but are not good climbers. A spider running across the ceiling or high on the wall is probably not a hobo spider. However, hobos can climb carpeted or other textured surfaces.
Hobo spiders spin funnel webs, which are flat, trampoline-like webs of nonsticky silk with a tubular retreat (Figure 2). They usually build webs outdoors around any low landscape feature with cracks or crevices. The web by itself does not definitively identify the hobo spider because other species of funnel-web weavers also occur in Idaho.
Hobo Spider Bites
Early evidence suggested hobo spider bites cause slow-healing, ulcerating lesions. That early evidence has since been refuted, and spider experts no longer consider them to be a threat to human health. Accordingly, the Centers for Disease Control and Prevention removed the hobo spider from its official list of venomous (harmful) spiders in 2015. Hobos can bite, but they are not poisonous to people.
Control of Hobo Spiders
- Eliminate outdoor habitats such as dense vines along windows and shrubs, rocks, and coarse bark mulches next to foundations. Consider replacing these materials with finer-grained products that do not create favorable spider habitat. Stack firewood away from buildings.
- Spiderproof your home by weather stripping and caulking around doors, windows, and utility lines. Fill cracks in siding and around the foundation. This will help keep out other invading insects that serve as a food source for spiders.
- Protect yourself from bites when working around spider habitats by wearing gloves.
- If hobos and other spiders still routinely enter your home, consider applying insecticides in a 1–2-foot band around and on the foundation and near windows and doors. Products containing the following pest-killing active ingredients should be effective as foundation sprays: bifenthrin, carbaryl, cyfluthrin, deltamethrin, imidacloprid, and permethrin, among others. A single treatment should provide control for 10–14 days.
- Strategically place sticky spider traps next to doors, along walls, behind furniture, and near window wells. Deploy traps midsummer through the first fall days of freezing temperatures.
- Inspect firewood for spiders and egg sacs and remove them before bringing firewood inside.
- Vacuum in corners and behind furniture to remove insects, spiders, webs, and egg cases. Empty vacuum waste into a ziplock bag to prevent surviving spiders from reentering the home.
- Discard clutter that provides habitat and hiding places for spiders.
- Move beds and bedding away from walls and flooring midsummer to October.
About the Authors
ALWAYS read and follow the instructions printed on the pesticide label. The pesticide recommendations in this UI publication do not substitute for instructions on the label. Pesticide laws and labels change frequently and may have changed since this publication was written. Some pesticides may have been withdrawn or had certain uses prohibited. Use pesticides with care. Do not use a pesticide unless the specific plant, animal, or other application site is specifically listed on the label. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.
Trade Names—To simplify information, trade names have been used. No endorsement of named products is intended nor is criticism implied of similar products not mentioned.
Groundwater—To protect groundwater, when there is a choice of pesticides, the applicator should use the product least likely to leach.
Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Barbara Petty, Director of University of Idaho Extension, University of Idaho, Moscow, Idaho 83844. The University of Idaho has a policy of nondiscrimination on the basis of race, color, religion, national origin, sex, sexual orientation, gender identity/expression, age, disability or status as a Vietnam-era veteran.
CIS 1221 | Published July 2016 | © 2022 by the University of Idaho