The Black Widow Spider (Latrodectus spp.) is a spider notorious for its neurotoxic venom found throughout the world and commonly associated with urban habitats or agricultural areas.
Although the common name ‘Black Widow Spider’ is most commonly used to refer to the three North American species best known for their dark coloration and red hourglass pattern, it is occasionally also applied to several other members of the Latrodectus (widow spider) genus in which there are 31 recognized species including the Australian Red-Back, Brown Widow Spider (sometimes called the grey widow), and the Red Widow Spider. In South Africa, widow spiders are also known as the Button Spiders.
Although their venom is extremely potent, these spiders are not especially large. Compared to many other species of spiders, their chelicerae are not very large or powerful. In the case of a mature female, the hollow, needle shaped part of each chelicera, the part that penetrates the skin, is approximately 1.0mm (around .04 inch) long, sufficiently long enough to inject venom to a dangerous depth. The males, being much smaller, inject far less venom and not so deeply.
The actual amount injected, even by a mature female, is very small in physical volume. When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose (though it can produce the very unpleasant symptoms of Latrodectism). Deaths in healthy adults from Latrodectus bites are relatively rare in terms of the number of bites per thousand people. Only 63 deaths were reported in the United States between 1950 and 1989 (Miller, 1992).
On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, world-wide, to widow bites than are exposed to bites of more dangerous spiders, so the highest number of deaths world-wide are caused by members of their genus. Widow spiders have more potent venom than most spiders, and prior to the development of antivenin, 5% of reported bites result in fatalities.