Black Widow Spider - Latrodectus mactans

Black Widow

The black widow spider, found worldwide, is infamous for its neurotoxic venom. There are three species commonly called black widow in North America: The southern black widow (L. mactans), the northern black widow (L. variolus), and the western black widow (L. hesperus).
All spiders, with the exception of one family, the Uloboridae (cribellate orb weavers), have venom glands. Spider venom falls into two categories: neurotoxic and cytotoxic. Neurotoxic venoms interfere with the transmission of nerve impulses to the muscles, frequently causing spasm and paralysis. Neurotoxins act rapidly, important to spiders confronted with large or dangerous prey intent on escape or retaliation. Cytotoxins, on the other hand, act more slowly. They principally act to slow down the prey, and actually begin the process of digestion by liquefying the tissues of the prey. Such venom can cause tissue necrosis in mammals, wherein the flesh surrounding an injection site dies, and heals very slowly or not at all. The brown recluse spider uses cytotoxic venom.

Adult female black widow spiders are gloss black with an hourglass shaped marking on the underside of its abdomen. They also bear a small, usually red (colors vary) dot near the spinnerets, which is separate from the hourglass. In L. variolus, the two halves of the hourglass shape may be separated into two separate patches.
A large female black widow spider can grow to about 1.5 inches (37 mm), counting leg-span. The body is about 0.5-0.6 inches (12-15 mm). Male black widow spiders are half the size of the female. They have longer legs and a smaller abdomen in relation to their body size. They are also usually dark brown with varying colors of stripes/dots, with no hourglass mark. Adult males can be distinguished from juvenile females by their more-slender body, longer legs and large pedipalps.

Black widow spiders typically prey on a variety of insects, but occasionally they do feed upon woodlice, diplopods, chilopods and other arachnids. When prey becomes entangled the web, the spider quickly comes out of its retreat, wraps the prey securely in its strong web, then envenomates it. The venom takes about ten minutes to take effect.

A sexually mature male spins a "sperm web", deposits semen on it, and charges his palpi with the sperm. The male then inserts his palpus into the female's spermathecal openings. The female deposits her eggs in a globular silken container in which they remain camouflaged and guarded. A female black widow spider can produce four to nine egg sacs in one summer, each containing about 100-400 eggs. Usually, eggs incubate for twenty to thirty days.
Black widow females can live five years, while a male's lifespan is much shorter. The female only rarely eats the male after mating, and L. mactans is the only black widow species for which this form of sexual cannibalism has been observed in the wild.

Black Widow Spider - Latrodectus mactans

Black widows build irregular webs of coarse silk, usually near the ground in dark places, and usually outdoors. Webs are often built among leaf litter on the ground in deciduous forests. They are also found under rocks or logs, in wood piles, in mammal burrows, and in dark corners of sheds, garages, crawl spaces, cellars, and basements. The spiders hang in an inverted position in these webs, do not leave them voluntarily, and are clumsy and completely out of their element away from them.

Habitat: Among fallen branches and among objects of many kinds, including wood piles, barbeque grills, sheltered places outdoors.

Range: Florida to Massachusetts, west to California. Texas, Oklahoma and Kansas; more prevalent in the south. I've lived near Chicago all my life, and I have never seen one here.
Life Cycle: Female does not leave web, is fiercely protective of egg mass, biting defensively if disturbed. Spiderlings disperse almost immediately after hatching.

Cobweb spiders (family Theridiidae) are also known as comb-footed spiders, after the 6-10 comblike bristles on the hind tarsi of most species. They usually have 8 eyes, sometimes six. They spin irregular webs and use the combs on their legs to fling silk over any prey that blunders into the web. The victim is then hauled to a remote area of web and injected with venom. There are more than 200 species in North America.

Male black widow has proportionately longer legs than female.