Steatoda grossa, one of at least eight Steatoda species occurring in the United States, is found along the coastal states of the Atlantic, Gulf, and Pacific regions. In the southern and western states, it is a common spider in homes and other structures, where it makes an irregular web (a trait shared by most comb-footed spiders) and is reported to capture and prey upon other spiders, including the true black widow spiders. Female Steatoda spiders have been reported to live for up to six years (males live for a year to a year and a half), producing numerous offspring.
Similar to the true black widow, the false black widow female is 6 to 10.5 millimeters in length, but it lacks the red hourglass pattern on the underside of the abdomen, which is more oval in shape than that of the true black widow. In most specimens, the abdomen has a purplish-brown to black color with light, pale yellow to grayish markings. In many specimens, these markings may be faded and difficult to see. The cephalothorax is a red-brown color with slightly darker legs.
These spiders mate in the spring, and the females can produce three or more egg sacs or cocoons from May through July. Each sac can contain 200 or more cream-colored eggs. Although the males can live for up to 18 months, they die shortly after mating. All stages of the immature spiders can be found in human-made structures throughout the year, as can the adults. Outside, these spiders can be found on low-growing foliage, under bark, in rock crevices, and under bridges.
A closely related species, S. borealis, is similar in shape and coloration but is slightly smaller. This spider is more common in the northern states (Pennsylvania included) and can be found in dwellings throughout the year.
False black widows produce symptoms that are similar to but much less severe than those of a true black widow bite. There are documented cases of Steatoda bites leading to blistering at the site of the bite and a general malaise lasting for several days. Additionally, symptoms can include moderate to severe pain increasing for the first hour (did not include diaphoresis) and occasionally, mild to moderate nausea, headache, and lethargy. The duration of all symptoms and effects ranged from 1 to 60 hours.
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Authored by: Steve Jacobs, Sr. Extension Associate
March 2002 Revised 2015