Black widow spiders are members of the genus Latrodectus, also known as the “true widow” spiders. Included in this group are the red widow, the brown widow, and several species known as “black widows”. These spiders are found in various continents, including North America, Europe, Asia and Australia.
Previously all North American black widow spiders were classified as a single species, L. mactans. However, they are now recognized as separated into three species. All black widows are very small spiders, with females’ bodies measuring about ½ inch in length (about 1.5 inches including their long legs). Males are even smaller.
Female black widow spiders are usually a shiny black in coloration, with a large round abdomen (the rear portion of the body), and eight thin legs. They often have a red hourglass shaped marking on the underside of their abdomen. In North American species, they may have other red markings on their abdomen, or in the case of the northern black widow, white markings on their abdomen and red on their legs.
The black widow species found in Australia and New Zealand have red markings on the upper side of their abdomen, while the Mediterranean black widow (found in Europe and Asia) has thirteen spots on its abdomen, which are usually red, but may be yellow or white.
The Mediterranean widow is the black widow spider most commonly associated with a fatal bite. While all black widow species produce a painful bite with uncomfortable symptoms that may last for several days, they are almost never fatal. Only female widows bite, and typically only while defending their eggs.