Broad-Faced Sac Spider
Trachelas tranquillus ranges from New England and adjacent Canada, south to Georgia and Alabama, and west to Kansas and Minnesota. They are found outdoors walking on foliage; under leaf litter, stones, and boards; and on buildings under the windowsills and siding. They construct silken retreats, within which they hide during the day. Most occurrences of T. tranquillus in homes coincide with falling temperatures in autumn. They do not, as a rule, establish reproducing colonies in homes.
The females are 7 to 10 millimeters in length; the males are 5 to 6 millimeters. The chelicerae and carapace are thick, hard, reddish-brown, and covered with what appear to be tiny punctures. The abdomen is pale yellow to light gray, with a slightly darker dorsal stripe. The front pair of legs is darker and thicker; the other three pairs become increasingly lighter and thinner toward the last pair.
These spiders prefer warmer and drier habitats. They can be found at the bases of plants, on fences, inside rolled leaves, and under stones and boards. Mature females are often collected while they wander around in homes during the autumn. Males mature and mate in midsummer, and each female will deposit a pure white egg sac containing 30 to 50 eggs in September or October. A common oviposition site is under loose tree bark. A peculiar trait of this spider is its reported tendency to scavenge on dead spiders and insects.
The broad-faced sac spider has been reported to produce a painful bite. There are records of severe secondary infection associated with the bite. It has been suggested that these infections may result from the spider’s propensity for feeding on dead and decaying arthropods. Typically, the bite produces a painful erythema similar to that of a bee or wasp sting. Individuals who are sensitive to arthropod venoms may exhibit a more severe and possibly systemic reaction.
Authored by: Steve Jacobs, Sr. Extension Associate
March 2002 Revised 2015
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