The shiny black body and legs of the Southern Black Widow (Latrodectus mactans) are striking. The globose abdomen is typically decorated on its underside with a red hourglass-shaped marking. In some individuals, the hourglass may be separated into two parts and in young females, especially, there may be a row of red spots extending down the upper side of the abdomen (the slightly larger Northern Black Widow, L. variolus, which has an overlapping distribution but is more common in the northern part of its range, nearly always has these dorsal spots and the hourglass marking in two parts). The much smaller male has a more red-orange hourglass marking and a continuous or broken red-orange stripe bordered by white down the dorsal midline of the absomen, as well as four pairs of diagonal white stripes along the sides of the abdomen. Young females often show a pattern similar to that of males. Female length is around 8 to 10 mm, but males are only 3.2 to 4 mm long.
The Southern Black Widow makes an irregular web of very strong and coarse silk, usually near the ground around tree stumps, in woodpiles, under stones and loose bark, around water faucets, in holes in the ground, and in garages, barns, storage buildings, and outhouses. When possible, it will retreat in the presence of a human interloper. Often the egg sac can be seen within the irregular web, guarded by the female. The nearly spherical egg sac is white to light brown, around 10 to 12 mm in diameter, and pear-shaped or with a distinctive nipple-like protrusion at the top.
Although the Southern Black Widow is widely distributed in North America and can be found in every U.S. state except Alaska, it is more common east of Kansas, Oklahoma, and Texas and especially in the southeastern United States, where most reported human fatalities have occurred. Most people who are bitten by these spiders have accidentally trapped the spider against their body or touched the web. The bite of the female contains a potent neurotoxin. Two red puncture marks can often be seen at the bite site and there is often a dull numbing pain around this area which may persist for 48 hours. This is accompanied by severe abdominal pain and a boardlike, rigid abdomen along with rigidity and spasming of all large muscle groups. Tightness in the chest and pain when breathing are common. Convulsions, paralysis, and shock can occur. Reportedly, four to five percent of untreated bites lead to death. Thus, anyone bitten by a black widow should seek professional medical attention immediately. Vetter and Isbister (2008) provide a recent review of medical aspects of spider bites.
(Kaston 1978; Howell and Jenkins 2004)
- Howell, W.M. and R.L. Jenkins. 2004. Spiders of the Eastern United States: a Photographic Guide. Pearson Education, Boston.
- Kaston, B.J. 1978. How to Know the Spiders, 3rd edition. Wm. C. Brown Company, Dubuque, Iowa.
- Vetter, R.S. and G.K. Isbister. 2008. Medical aspects of spider bites. Annual Review of Entomology 53: 409-29.