Despite extensive media hype and paranoia relative to black widow, brown recluse, and hobo spiders, bites from these species are actually quite rare. The likely perpetrators of most spider bites are sac spiders, with yellow sac spiders being the most harmful to humans.
What is a Yellow Sac Spider?
According to Dr. Susan C. Jones, entomologist at Ohio State University, two similar species of sac spiders (Cheiracanthium inclusum and Cheiracanthium mildei) are collectively referred to as "yellow sac spiders." The color identification in their name, however, can be a little deceiving - yellow sac spiders generally are not yellow. According to Dr. Jones,
"[T]hey are light yellow to pale yellowish green, sometimes with a orange-brown stripe on top of the abdomen . . . An adult female sac spider's body typically is 1/4- to 3/8-inch long, and her leg span is up to 1 inch. Males are more slender, with a slightly larger leg span. The first pair of legs is longer than the fourth. These spiders have eight similarly-sized dark eyes arranged in two horizontal rows."
Yellow sac spiders may also be tan or light brown in color.
Where Do Yellow Sac Spiders Live?
Cheiracanthium inclusum can be found all across the United States. Cheiracanthium mildei, like the hobo spider, came over to the United States from Europe around the 1940s. It is centralized around Seattle, Washington, but its range expands out across the Pacific Northwest and Southwestern Canada.
Yellow sac spiders are generally outdoor spiders, preferring foliage to structure, at least in warmer climates or seasons. But sac spiders are hunters, and they will search for prey indoors when there is little to be found outside. Thus, in the fall, they may move inside dwellings if they can find a food source therein.
According to Dr. Barb Ogg of the University of Nebraska, sac spiders are nocturnal hunters. "Indoors, they can be observed on walls and ceilings, but drop to the floor to seek cover when disturbed . . . Sac spiders construct a silken tube or sac in a protected area, such as within a leaf, under landscape timbers or logs, or at the junction of a wall and ceiling, and they use this sac as their daytime retreat. This is how the sac spider gets its name. These spiders do not build webs."
Are Yellow Sac Spiders Venomous? Are They Dangerous to Humans?
Yellow sac spiders are venomous. The effects of their bites resemble those of the brown recluse and hobo spiders, although not nearly as severe. Plus, they heal more rapidly.
Yellow sac spider venom is "cytotoxic," which basically means that it kills cell tissue. The harm, however, is localized. The bite itself may feel similar to a bee sting. It will likely redden and get itchy, and it may result in a blister.
On rare occasions, a small necrotic lesion may form. According to arachnologist Darwin K. Vest, "Systemic effects are usually not severe, but when they occur may include chills, fever, headache, dizziness, nausea, anorexia, and sometimes shock."
Again, these symptoms are in extreme case. Most people are left with an itchy bump that disappears within a few days. Although bites are fairly common, "sac spiders typically do not bite unless they are trapped against the skin or provoked," says Dr. Jones.
How Does One Remove Yellow Sac Spiders from Dwellings? How are Bites Prevented?
Yellow sac spiders are nocturnal, which means that by day, they are probably in their sacs. These are usually readily visible and can simply be vacuumed up, spiders, eggs, and sacs all at once. General pest control may also help limit a sac spider infestation. The fewer the insects, the fewer the food sources for sac spiders. Shaking out clothes left on the floor or in closets before wearing and keeping beds away from the walls may help to prevent roaming sac spiders from coming into human contact.
Humans and yellow sac spiders can peaceably co-exist with the likelihood of serious human harm being slight. However, if after receiving a spider bite one experiences the above-described symptoms, he or she should contact healthcare professionals immediately.
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