"The Black Widow Spiders" (Latrodectus spp.)

No other group of spiders causes so much apprehension. The taxonomic status of black widow species in the United States have been under dispute for some time. Levi and Randolf (1975) lists L. mactans, L. bishopi, L. geometricus, L. variolus and L. hesperus. However, these authors doubt L. hesperus is a valid species and suggest L. mactans and L. variolus are species complexes. Although Levi doubts the occurrence of L. mactans in New England, Kaston (1976) holds L. variolus and L. mactans both are found in New England. It is apparent museum taxonomy (Kaston, 1970; Levi and Randolph, 1975) alone will not be able to settle the nomenclatural status of black widows. While there is much variation in color and certain other characters among populations of widows, the definitive male palpal and the female epigynumal characters of matures are too much alike in the related species.

Distribution. Black widows are present in every state in the United States, in southern Canada, Caribbean Islands, Mexico, Central and South America, Mediterranean countries, southern Russia, New Zealand, Australia and other warmer parts of the world. Widows frequently are found in railroad boxcars, shipholds, interstate freight vans and other transport. Thus, northward import of southern species and the introduction of exotic species are fairly common. In northern states, outbreaks or "blooms" of black widows occur erratically. Some years an area may have thousands of widows and the next year they may be gone. Certain kinds of habitats such as sand dune areas, e.g., Illinois Beach State Park (about 30 miles north of Chicago), have black widows every year. Apparently, alternating warm spells and cold snaps in the winter and spring are detrimental to survival. In much of California, the southwest and the south, widows do extremely well.

Preying habits. The female constructs an irregular, tangled, criss-cross web of rather coarse silk. The core of the web is a silken tunnel, in which the female spends most of the daylight hours. The web usually projects in all directions from a few inches to a few feet. The web is regularly renewed, altered, and expanded and is capable of securing large insects.

Once a prey is caught in the web, it is wrapped-up in silk which is spun out in great abundance. As the prey becomes covered with silk, it is turned over and over by the widow with her legs as more silk is applied. After the victim is secured, it is killed by a bite of the chelicerae. After the poison is injected, the prey may be fed upon or be reserved for a later feeding. During feeding a powerfull saliva is released from the foregut which dissolves the protein tissue of the prey. After the prey is fed upon and the body fluids are sucked from the victim, the carcass is cut loose and allowed to drop to the ground. A variety of insects and other arthropods are eaten or imbibed.

Life History. The eggs are laid in silken cocoons or sacs which are globular in form and about 1/2 inch in diameter. When first constructed, the sacs are white, but after a while turn pale brown. One to three hours are required to construct the egg sacs. About 300 to 400 eggs per sac is common, although Lawson (1933) reported a sac with 917 eggs. From four to nine egg sacs may be produced by a female during a summer. The female guards the egg sacs and moves them as necessary to repair her web. After laying eggs, the females are hungry and more likely to bite a human. The eggs hatch in about eight to 10 days. The spiderlings molt once before emerging from the sac. The period between the depositing of the eggs and emergence may be two weeks to a month. The spiderlings force an opening in the sac, usually at night. At first, the second instar spiderlings remain near the sac, but after a few hours to several days, they climb to a promontory point, where air currents are suitable, spin silk strands and float out on the breeze, like a kite on a silk thread. This ballooning scatters the spiderlings to whatever fate awaits them.

After they land, the spiderlings construct a web, obtain pray, and if successful, pass through some seven more instars when they become mature adults. Depending upon the availability of prey, maturity comes after about four months. A generation is completed in about one year. In warmer climates, development continues throughout the year. In the North, winter is spend in preadult stages with mating occurring in about May and egg laying following shortly thereafter. Deevey and Deevey (1945) found the average male matures in about 71 days after emergence from the egg sac and lives about 30 days longer if alone. The average female matures 92 days after emergence and lives about 179 days longer. The maximum longevity was 160 days for males and 550 for females. Kaston (1948) reported the survival of one female for 1,063 days after emergence from the egg sac.

Mating. Popular belief has the male eaten after one encounter with a female. Ordinarily, if the females are well fed, most males get away to mate another day. The observations in which males are eaten usually occur under laboratory conditions which are not natural and may not represent what is normal. Ross and Smith (1979) suggest males and females have chemo-receptive hairs on the tarsi and pedipalps and complementary contact pheromones are produced which are incorporated into the silk. These sustances function in mate location, sex identification and courtship. Web vibration by the male and reciprocating movements by the female enter into the courtship. But the ferocity of the female towards her mate has been much over-played. Actually, males live much longer when associated with a mate, because he is a king of parasite on the food captured in the female's web. The females support their free-loading husbands. What more can any male ask?