Which spiders are potential threats?
Most spiders are not poisonous to human beings. There are about 3,000 different spiders in North America, but only a few of them cause problems for people.(2) If you are bitten, try to capture the spider that bit you if you can catch it quickly and safely. Later, if needed, you can get an accurate identification of the spider.(3)
Tarantulas are large, hairy spiders found in the southern United States. Scary to some because of their large size, these spiders are not as dangerous as is commonly thought. Their bite causes little lasting pain or serious problems. However, their hairs can can cause an allergic response.(2)
The black widow female, but not the male, is big enough to bite a person. She is about 1/2 an inch long and shiny black.(1) She is easily recognized by the red hourglass design on the bottom of her abdomen.(4) Black widows are found throughout the Northwest.(1,2,4,5) They tend to live in dark, dry, undisturbed places including garages, barns, sheds, wood piles, and outhouses.(1) Most bites occur when cleaning out or picking up objects in these kinds of places. If you are bitten, the pain spreads from the bite to other places. Sometimes spasms occur. Children, elderly people, and people with other problems are likely to have more severe symptoms.(1) If you are bitten you should get medical attention.(4)
Brown Recluse Spiders
Brown recluse spiders come in various shades of brown. They have black violin- shaped markings on the back of the cephalothorax, although sometimes this can be hard to see. They have six eyes (most spiders have eight) and fine hairs on their legs and abdomen.(6) Brown recluse spiders are common in the central Midwest and South. They do not occur in the Pacific Northwest except when they hitch-hike from elsewhere. (2) California deserts have some native relatives of the brown recluse, and a South American relative has become established in the Los Angeles area. (6) Brown recluse spiders are shy (as their name implies) and active at night. They are often found under trash cans, tarps, and in similar locations.(6) Their bite causes stinging, followed by intense pain. A blister forms at the bite and the area becomes swollen; later the tissue dies, leaving an ugly scar.(4)
Hobo Spiders (Aggressive House Spiders)
The hobo spider is common in the Pacific Northwest. It has long legs and chevrons on its abdomen.(5) It is common in basements and window wells, and is usually found on the ground floor of a house. It is called "aggressive" because it bites willingly if it is cornered.(4) Bites from this spider are relatively rare, but do cause open, localized wounds that can take a long time to heal.
1. University of California. Division of Agriculture and Natural Resources. 2000. Spiders. Pest notes. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7442.html
2. Washington State University Extension. Undated. Spiders. EB 1548. http://cru.cahe.wsu.edu/CEPublications/eb1548/eb1548.html
3. U.S. National Library of Medicine and the National Institutes of Health. 2005. MedlinePlus medical encyclopedia: Insect bites and stings. http://www.nlm.nih.gov/medlineplus/ency/article/000033.htm
4. Montana State University Extension Service. 2005. Spider identification and management. MT 199210. http://msuextension.org/publications/AgandNaturalResources/MT199210AG.pdf
5. Oregon State University. 2005. Poisonous spiders, ticks and other biting mites in Oregon. http://www.ent.orst.edu/urban/spiders.html
6. University of California. Division of Agriculture and Natural Resources. Brown recluse and other recluse spiders. Pest notes. 2000. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7468.html
O'Toole, C. ed. 2002. Firefly encyclopedia of insects and spiders. Buffalo NY: Firefly Books, Ltd.
Appropriate Technology Transfer for Rural Areas. 2000. Farmscaping to enhance biological control. http://www.attra.org/attra-pub/farmscape.htmlA fact sheet on hobo spiders is available at: University of California. Division of Agriculture and Natural Resources. 2006. Hobo Spider. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7488.html