When it comes to dangerous spiders in the United States, black widows have long been the most notorious species. Reports describing dangerous, and even fatal, black widow bites started during the late 19th century when scientific documentation and record keeping was becoming more commonplace. Today, the black widow bite remains the most common cause of medically significant spider bite symptoms in the country, and these intimidating arachnids can be found in most areas in the US. Black widows belongs to the Latrodectus spider genus, which is comprised of more than two dozen urban-dwelling and highly venomous spider species worldwide.

Five Latrodectus species can be found in the US, two of which are documented in Louisiana where they are not infrequently reported as pests within homes and other structures. One of these species, commonly known as the brown widow, has recently been introduced into Louisiana. This alien spider species has been proliferating and spreading rapidly throughout the state, and their bites have been documented as causing serious medical symptoms. However, Latrodectus mactans, or the southern black widow, is responsible for the majority of medically significant spider envenomations in the country, and surprisingly, freshly hatched baby spiderlings of this species are not necessarily harmless either.

Black widows are often found in homes, but they are most frequently encountered in low-traffic indoor areas, such as garages, storage closets, sheds, barns, crawl spaces, cellars, basements and sometimes attic spaces. The southern black widow’s presence within a home can be recognized by the presence of tattered webs that usually measure 35 cm in both length and width, but they can be much larger. These webs are almost always located at elevated positions between 8 and 12 feet from the floor in dark corners and around ceiling rafters.

Southern black widow eggs sacs can be recognized for their grey and spherical appearance, and are generally around 9.5 mm in diameter with a conspicuous notch on the top. Each egg sac contains an average of 255 cream or yellow-colored eggs, and each female is usually in possession of 10 egg sacs. These eggs sacs can be constructed by females in as little as an hour within a home, and the spiderlings that hatch are particularly poisonous. However, due to their lack of developed mouthparts, spiderlings are only dangerous when ingested, but pets may die after consuming a spiderling.

Have you ever encountered an indoor spider egg sac? If so, did you learn which species the egg sac belonged to?