Latrodectus mactans
black widow spider

Within the United States, Latrodectus mactans ranges as far north as Massachusetts and New Hampshire, as far south as Florida, and as far west as California, Texas, Oklahoma and Kansas. The black widow spider also occurs throughout all four deserts of the American southwest. In addition, Latrodectus mactans is found in Canada, Mexico, the West Indies, and South America. (Comstock, 1948; Desert USA Magazine, 2004; Emerton, 1961; Milne and Milne, 1990; Shuttlesworth, 1959; Smith, 1980)

A terrestrial environment is the habitat of the Latrodectus mactans. It is ubiquitous and builds strong-walled retreats quite close to the ground and in dark sheltered spots. However, it also spreads its snares over plants. Webs of the black widow spider can be found in recesses under stones or logs in a woodpile, in crevices or holes in dirt embankments, in barns and outbuildings. They can also be found around lids of dust bins, around seats of outdoor privies, spaces under chips of wood, around stacked materials of any kind, in deserted animal burrows or rodent holes, and entwined in grape arbors. This spider may find its way into clothing or shoes and occasionally seeks a spot in a house to build a web, but it is usually not found indoors. When it does seek shelter in a building, it is due to cold weather and a need for a dry shelter. In addition, in the eastern United States, Latrodectus mactans is associated with littered areas, with dumps of large cities, with garages, and storage sheds. In arid parts of Arizona, this spider inhabits almost every crevice in the soil and its nests are found in cholla cacti and agave plants. (Ferrand, 1988; Kaston, 1953; Preston-Mafham, 1984; Comstock, 1948; Gertsch, 1979; Shuttlesworth, 1959; Snow, 1970; Smith, 1980; Emerton, 1961; “Black Widow Spider, www.nscu.edu)

Biomes: temperate and tropical zones, including temperate forest, tropical rainforest,

temperate grassland, chaparral, desert

Latrodectus mactans is the largest spider of the family Theridiidae. The black widow spider is shiny, coal black in color. The female averages 8-10 mm in length and has long slender legs and a round abdomen. Usually on the underside of the female’s abdomen (venter) is a red hourglass mark and one or two red spots over the spinnerets and along the middle of her back. The male is 3-4 mm long with an elongated abdomen. The male’s legs are larger than the female’s and each joint is orange brown in the middle and black on the ends. On the sides of the male’s abdomen there are four pairs of red and white stripes. Young spiderlings, or juveniles, are orange, brown and white; they acquire their black coloring with age, or with each molt. (Emerton, 1961; Milne, 1990; Comstock, 1948; Kaston, 1953)

Another important characteristic of Latrodectus mactans is its “comb foot.” The spider has a row of strong, curved bristles on the hind pair of legs, which form a distinct comb. The comb is used for flinging silk over its prey. (Shuttlesworth, 1959; Comstock, 1948)

Once the female produces her egg sacs she guards them until the spiderlings hatch. Once the spiderlings have hatched they leave the web (Milne, 1990).

Most spiders live for one year. Some are known to have lived 3 years in the wild, and in captivity, widow spiders may live for at least four years.

Latrodectus mactans is timid, sedentary, solitary, cannibalistic, and nocturnal. The only social life it exhibits is when it mates. During the daylight hours, this spider spends its time in the silken tunnel of its web, which is the core of the snare. The female black widow spider hangs upside down in her web; her red hourglass marking is a visible warning signal. This spider will drop out of its web at the slightest disturbance and pretend that it is dead. The female black widow is usually clumsy when she is not in intimate contact with the lines of her snare. Latrodectus mactans is a tangled web weaver. Its irregular, funnel-shaped web of coarse silk has a definite plan. Three structural levels can be recognized: an uppermost complex of supporting threads, a central zone of tangle threads, and a lower zone of vertical trap threads. Also, the black widow spider is greatly active in the autumn months and its web is spread over everything. In addition, most of these spiders live only a year, but the yearly population is divided into two faunas, one identified with spring and the second with fall. (Ferrand, 1988; Shuttlesworth, 1959; Preston-Mafham, 1996; Hillyard, 1994; Gertsch, 1979; Kaston, 1953)

Latrodectus mactans is exclusively carnivorous and antagonistic. Ordinarily it feeds on insects; however, it also consumes wood lice, diplopods, chilopods and other arachnids. Usually, the black widow spider enswathes prey caught in its snare, bites it, and later drags it to its hub, or retreat, to be eaten. Latrodectus mactans inflicts a small wound on its prey, uses its cheliceral teeth to mash it up, pours digestive enzymes on the prey; and sucks up the resulting food. The whole digestion process takes place outside the spider’s body. (Kaston, 1953; Snow, 1970; Preston-Mafham, 1996; Foelix, 1996; Levine and Miller, 1991; Gertsch, 1979)

A known predator is the mud-dauber wasp (Desert USA Magazine, 2004). The black widow spider spins a web which acts as a defense mechanism against predators. When a possible predator comes in contact with the web, it becomes entangled in the threads allowing the spider to wrap more silk around it and then inject it with its poison. Also, the female spider hangs upside down in her web so that her red hourglass mark serves as a warning signal to a predator (Farrand, 1988). (Desert USA Magazine, 2004; Farrand, 1988)

The black widow spider creates its own habitat wherever it spins its own web. With the aid of its web, the spider plays an active role in the ecosystem by helping to control insect populations.

While Latrodectus mactans are not aggressive and do not have the instinct to bite, their venom is neurotoxic, which means that it blocks the transmission of nerve impulses. If the black widow spider bites, most likely it has been pressed against human bare skin, and this causes a natural reaction, a bite in self-defense. A bitten human suffers from a painful rigidity in the abdominal wall muscles. While the poison from this spider is serious, it is rarely fatal. If treated properly and promptly, the victim completely recovers. A black widow's bite is distinguished by a double puncture wound. Children and adults who are not in good physical condition suffer the most from the bite. It is reported that the venom of Latrodectus mactans is 15 times more toxic than a rattlesnake’s. (Comstock, 1948; Gertsch, 1979; Hillyard, 1994; Kaston, 1953; Preston-Mafham and Preston-Mafham, 1996; Shuttlesworth, 1959)

On the positive side, Latrodectus mactans consumes enormous numbers of harmful insects. It gets rid of troublesome flies and mosquitoes,which carry diseases, as well as locusts and grasshoppers, which destroy grain crops. In addition, this spider ingests beetles and caterpillars, which defoliate plants and trees. The black widow’s entrapment of pests makes it invaluable to man and helps to balance nature. (Kaston, 1953; Shuttlesworth, 1959; Preston-Mafham, 1984) Furthermore, the silk and venom Latrodectus mactans produces has potential uses in biotechnology. Its venom could lead to a new generation of environmentally safe insecticides that leave no residues. Drugs derived from its venom may be able to save lives of future heart attack victims by means of an immediate effect on the blood vessels, allowing the blood to flow more easily. (Hillyard, 1994; Kaston, 1953; Preston-Mafham and Preston-Mafham, 1984; Shuttlesworth, 1959)

Black widow spiders are fairly common and they are afforded no special conservation protections.

Latrodectus mactans goes by several names. It received the name “widow” because females sometimes kill and eats their mates after mating has taken place. However, the sexes can separate peaceably and the male may even mate again (Farrand, 1988; Kaston, 1953). Other names that are associated with the black widow spider are “the hourglass spider” because of the red hourglass shaped mark on the female’s abdomen or “the shoe button spider” due to the form of the spider’s jet-black abdomen (Shuttlesworth, 1959). (Farrand, 1988; Kaston, 1953; Shuttlesworth, 1959)