Spiders are not insects; they are arachnids. Insects have three body segments and three pairs of legs, while spiders have two body segments and four pairs of legs. However, the distinction can go unappreciated when one of the eight-legged creatures is scurrying across your kitchen floor or loitering in a web directly over your favorite easy chair. Although it is not always easy for the average homeowner to identify a spider, even under magnification, the task can be made easier by limiting the options to just those spiders that are commonly found inside homes in your area.
Western Black Widow (Latrodoctus hesperus)
Although virtually all spiders are capable of injecting venom into prey, there are only about two dozen types that have venom potent enough to affect humans, and the black widow is one of them. A black widow can inflict a painful bite, and the venom can cause nausea, muscle pain and breathing difficulties, but unless the victim has an existing medical issue or is elderly or very young, the venom is rarely fatal and symptoms typically fade within three days.
As adults, females have a velvety black color, while immature females and males typically have white or yellow stripes. Adult females normally have two reddish marks on the underside of their abdomens that are reminiscent of an hourglass. Including their legs, adult females normally have a diameter of approximately 1.5 inches.
Hobo Spider (Tegenaria agrestis)
The hobo spider is commonly called the aggressive house spider. This term is inaccurate; they are not particularly aggressive toward humans although they will bite if threatened, and they spend most of their lives outdoors. However, they can establish webs in basements or other humid, dark areas. They may also wander into the rest of the home when searching for a mate, normally between the middle of summer and end of autumn.
Adult hobo spiders are between 1 and 1.75 inches in diameter, including their legs, and are light to medium brown in color with a pattern of chevrons on their backs. They are often misidentified as their appearance resembles a number of other spiders. Hobo spiders have been identified as brown recluse spiders, which are not found in Washington unless transported from another state. Giant house spiders, which are established in the state, are often mistaken for hobo spiders as they are very similar in appearance although the giant house spider does not have the chevron markings. Giant house spiders, however, are not believed to pose a risk to humans, while the venom of hobo spiders may cause necrotic tissue damage although there is no consensus among experts on this issue.
Wolf Spiders (Family Lycosidae)
Although wolf spiders tend to be darker in color and smaller than hobo spiders, the two are sometimes confused. Wolf spiders are a bit hairier than hobo spiders, and as they hunt for prey rather than ensnare it, wolf spiders do not produce the funnel webs associated with hobo and giant house spiders. Wolf spiders can enter buildings in pursuit of prey, but such incursions normally happen during cooler autumn months. The venom of the wolf spider is not considered to pose a serious danger to adult humans.
Yellow Sac Spiders (Cheiracanthium species)
Yellow sac spiders may be yellow, tan, greenish or light brown. They are small, typically between 1/4 and 3/8 inch in length, and their size, combined with their pale coloring and lack of conspicuous markings, make them easily overlooked. However, according to information from the University of Nebraska, sac spiders are believed to account for more bites to humans than any other spider. Their bites can cause nausea, muscle aches and necrotic tissue damage. Although they are considered outdoor spiders, when cooler weather diminishes their prey, they may invade homes and other buildings. If they have an available supply of small insects, they can remain indoors indefinitely.