Q: Are the dust gathering “cobwebs” caused by spiders?
A: Spiders of the family Theridiidae, or “cobweb spiders” are responsible for many of the loose, haphazard looking webs found in the corners of houses, barns, and sheds. The common house spider, Achaearanea tepidariorum (C.L. Koch), may be the most abundant of the several species of spiders living in the company of man in the southeastern United States. They are rather shy spiders displaying no aggression so we need not fear them. My only close encounter was in the shower – sadly the spider did not survive the hot water. I’m just not that fond of sharing my shower with arachnids. Females and juveniles make typical theridiid webs (tangle webs). These webs are frequently made between two adjoining edges of a building, for example, between an eave and a wall. Many individuals may occur in the same area and build nearly contiguous webs covering large areas of eaves, wall space, and window frames. Webs may be built both inside and outside of buildings; when inside, they are frequently a major contributor to the build-up of “cobwebs.” Sheds, barns and stables, in addition to other outdoor dwellings, may have heavy populations of this species. Other characteristic habitats include undersides of highway bridges and culverts. Like most spider webs, the webs of cobweb spiders are sticky. When the spiders move away or die, the abandoned webs start to collect airborne lint and dust. Although
A. tepidariorum belongs to the same family (Theridiidae) as the notorious black widow spiders (Latrodectus spp.), it is not known to be dangerous to humans. One case of serious allergic reaction to the bite of A. tepidariorum is known from Gainesville, Florida. But remember, all spiders carry venom and our reaction will vary from case to case. A single female may produce many pear-shaped light brown eggsacs during the year, which are hung freely in the web. At least in Florida, all stages seem to occur throughout the year. Most of the information provided came from this University of Florida publication: http://entnemdept.ufl.edu/creatures/urban/spiders/common_house_spider.htm