Identification: There are five widow spiders native to North America and all have smooth, bulbous abdomens and long spindly legs (as do most cobweb spiders). Females are much larger and generally less colorful than the males (which are small and generally not considered as dangerous). There is considerable variation in size and coloration between these five species, but most widow species can reach body lengths of nearly half an inch (>1cm) and legspans of over an inch (2-3cm). The western (L. hesperus), northern (L. variolus), and southern black widow (L. mactans) are generally black in coloration. Female northern black widow tends to have red spots on their abdomen while the southern and western black widows often lacks any dorsal pattern. Both southern and western black widows have complete red hourglasses under their abdomen while the northern black widow has a broken or disjunct hourglass (see image). The brown widow (L. geometricus) is usually white to dark brown in coloration with some white spots and lines on its abdomen. It has a complete yellow or orange hourglass under its abdomen. The red widow (L. bishopi) has a bright red cephalothorax and legs with a black abdomen with large red spots. In place of the typical hourglass under the abdomen, female red widows generally just have one or two red spots (Bartlett 2004, McCorkle 2002).
Distribution: Widow spiders are found througout most of North America but may be regionally rare or absent. These spiders are not known from some of the north-central plains and rocky mountain states. The northern black widow (L. variolus) is found throughout eastern North America while the southern black widow (L. mactans) occurs mainly in the southeastern states, with scattered records throughout the southwest and even in to Canada. The western black widow (L. hesperus) is found all along the west coast, throughout the southwestern states, in the southern Rockies and east in to Texas. The red widow (L. bishopi) is found only in the southern half of Florida in open scrub habitat. The brown widow is an exotic species that was originally introduced into Florida but has since spread throughout much of the southern United States and is primarily associated with human dwellings (Bartlett 2004, Garb et. al. 2004).
Ecology: Black widows are found in a range of natural habitats including mature forests, open fields, rocky glades, wood or brush piles, and rock faces. They build low webs that are extremely strong and sound almost like paper ripping when they are pulled apart. These webs often come out of a crevice where the spider remains during the day. Black widows occasionally show up in sheds, barns, and other old undisturbed buildings, but unlike the brown recluse, these spiders rarely show up in homes (McCorkle 2002). Brown widows are not native and are almost exclusively found in and around buildings and man-made structures where they may reach incredibly high densities. Conversely, the red widow is much more of a specialist that is strongly associated with scrub habitat in Florida where it builds its webs in low shrubby vegetation. Female widow spiders use their extensive and strong webs to capture a variety of invertebrate prey including some larger, hard-shelled beetles. The spiders kill their prey with their powerful venom before injecting digestive fluids to dissolve and consume the soft parts of their prey. Widow webs are often littered with the hard exoskeletons of their prey. It takes a few months for female widows to mature and they may survive for another six months or so. Males are very short-lived and spend most of their time wandering in search of females. Though females will occasionally eat the male after they have mated, this is not as common as most people believe and is no different from the behavior of most other spiders (Bartlett 2004).
Venom: Widow spiders have a potent neurotoxic venom and are generally considered the most dangerous spiders in North America. This being said, bites are rare and seldom fatal with some individuals having very minor reactions. Not all five species of widow spider in North America are considered equally dangerous as the non-native brown widow (L. geometricus) and the red widow (L. bishopi) are considered by many to have a weak venom that may not be medically significant (Bartlett 2004). The three species of black widow however do have potent venom and should be considered potentially dangerous. Bites only happen on the rare occasion when someone reaches into a dark space where a widow has made its web or when a spider somehow finds its way into clothing and gets pressed against skin. The bite itself is not painful and symptoms other than redness and swelling are not felt immediately. A few hours after the bite intense, often painful muscle spasms will begin to move from the bite site into the abdomen and back resulting in a sensation that has been likened to appendicitis. Immune compromised, very young, and elderly people are at higher risk for serious reactions from a bite and when medical treatment is not sought, a serious bite may result in more intense spasms and tremors, unconsiousness and in rare cases suffocation. Though the venom of this spider is extremely potent, such a small amount is injected that most people will fully recover especially if medical treatment is sought quickly (McCorkle 2002).
- Bartlett, T. 2004. “Genus Latrodectus – Widow Spiders” (Online), Bugguide.net. Accessed November 4, 2012 at http://bugguide.net/node/view/1999.
- Garb, J. E., A. Gonzalez, and R. G. Gillespie. 2004. The black widow spider genus Latrodectus (Araneae: Theridiidae): phylogeny, biogeography, and invasion history. Molecular Phylogenetics and Evolution, 31:1127-1142.
- McCorkle, M. 2002. “Latrodectus mactans” (Online), Animal Diversity Web. Accessed November 05, 2012 at http://animaldiversity.ummz.umich.edu/accounts/Latrodectus_mactans/.