The original reports, which suggest a mortality of 5 percent, were not well documented, and the true incidence is probably much lower. Clearing away old furniture, tires and other junk from yard areas will not greatly influence black widow populations, but will help reduce harborage for this spider. Because they prefer closed, dark places such as water meter compartments and crawl spaces, barriers constructed to inhibit entrance to these areas are of great value. Screening openings and plugging holes and crevices with steel wool or other material can help, especially with the larger individuals. See PB1303 for more ways to exclude pests from buildings.
Most spiders have little defense against insecticides and black widows are no exception.
Apply an insecticide to the habitats frequented by these spiders when you detect an infestation. For the common black widow, spot treat directly on the web where the spider is found or suspected. Since the vast majority of spiders and other arthropods are either harmless or beneficial, treat only if you have an infestation. Homeowners may find formulations containing permethrin, bifenthrin, tralomethrin, dursban and diazinion easier to locate in retail stores. The Black Widow Spider, PB1193, University of Tennessee Agricultural Extension Service.