Most spiders are harmless organisms that, rather than being dangerous to humans, are actually allies in the continuing battle to control insects. Most venom produced by spiders to kill prey is usually harmless to humans. However, there are two spiders in the United States that can produce severe or even fatal bites. They are the black widow spider (Latrodectus mactans) and the brown recluse spider (Loxosceles reclusa). Black widows are shiny black, with a bright red “hourglass” on the underside of the abdomen. The venom of the black widow is neurotoxic and affects the nervous system. About 4 out of 1,000 black widow bites have been reported as fatal. Brown recluse spiders have a violin-shaped strip on their back. The venom of the brown recluse is hemolytic and causes the death of tissues and skin surrounding the bite. Their bite can be mild to serious and sometimes fatal.