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)
Average mass: 1 g.
Average length: 3-10 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; venomous
Sexual Dimorphism: female larger