Potentially Dangerous Spiders

Spider Bites Research has shown that over 80% of suspected spider bites are caused by other arthropods, such as insects and ticks, or other disease states. Of the more than 3,000 kinds of spiders in the United States, about 60 species have been implicated as causing medically significant bites to people. Many spiders are not capable of breaking the skin with their fangs while other species contain venom that causes no reaction. Spiders are usually very timid and will only bite in self-defense if mishandled, cornered, or injured. Even when they bite, spiders do not always inject venom. The severity of the reaction to a spider bite will differ among individuals. Most spider bites are less painful than a bee sting. Actual spider bites show two puncture marks although the wound is not always obvious. A rather typical reaction may involve localized reddening and various degrees of swelling, itching, and pain. Within a few hours a small red, blue, or black discoloration can develop around the bite site. The area may remain tender for a few days, and eventually a small sore can develop that soon begins healing. Accurate identification of any spider bite can only be made if the spider causing the bite is captured and identified. Infrequently bites from some species of sac spiders, wolf spiders, jumping spiders, and cobweb weavers have been observed. There are two types of spiders in the United States, the widow and recluse spiders, that are infamous because of their venomous bites to people. Both the black widow (figure 1) and the brown recluse (figure 2) (neither of which is native to our area) are timid, nonaggressive spiders. Confirmed bites from these spiders are extremely rare in the Upper Midwest. Northern Widow Spider Bite The northern widow spider is infrequently found in the Upper Midwest. This species is one of the three closely related "black widows." Black widow spiders are shy and prefer secluded locations such as crawl spaces, attics, garages, and sheds where they construct a tangled, crisscross web. Common web locations are in stacked boards, firewood piles, in rubble, around water meters, under stones or other protected sites. Female northern widow spiders have round, shiny black abdomens, with two touching red triangles (the hour-glass marking) on the underside of the belly. They are up to 1⁄2 inch long. The female spends most of the daylight hours in a silken tunnel retreat and is helpless away from her web.