Black Widow Spider - Latrodectus mactans

The black widow spider (Latrodectus spp.) is noted for its neurotoxic venom. It is found worldwide. 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).

Adult female black widow spiders are gloss black with an hourglass shaped marking on the underside of its abdomen which can range from orange to red. 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 or smaller. 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 typical of most other male spiders.

As with many venomous creatures, the brightly colored markings serve as a warning to predators. Eating a black widow will normally not kill a small predator (birds, et cetera), but the sickness that follows digestion is enough for the creature to remember that the bright red marking means "do not eat." Because the adult female black widow typically hangs and moves about its web upside down, and because the web is typically close to the ground, its hourglass is visible to most predators. Juvenile female widows spend a large quantity of time in search of an optimal environment. Once an optimal location is found, adult female widows often spend their entire lives in one place. Because juvenile females must first find this optimal location, they bear brightly colored marks upon their backs, so that they may be seen by predators when walking using its legs. Males bear similar marks to the females to serve as warning while they are searching for mates, however, the marks are not as prominent (not as brightly colored, or as large). Males, being less venomous, are less of a threat to predators, so having less prominent but similar marks helps predators to better judge their prey (some large birds can eat male widows without adverse effect, and so only avoid female spiders; those who cannot eat any widow without adverse effect eat nothing with the marks). Female juveniles develop an hourglass before the dorsal markings are shed. As is characteristic of all arthropods, black widow spiders have a hard exoskeleton composed of chitin and protein. [2]

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. Rarely, do more than one hundred survive through this process. On average, thirty will survive through the first molting, due to cannibalism, lack of food, or lack of proper shelter. It takes two to four months for black widow spiders to mature enough to breed, however full maturation typically takes six to nine months. The females can live for up to five years, while a male's lifespan is much shorter. Contrary to popular belief, 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.

Female black widow shows diagnostic red hourglass mark

Black Widow Spider

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.
Web: Irregular mesh with funnel shaped retreat much like a funnel weaver spider's retreat.
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. Pear-shaped egg sac is pale brown. Female often eats the male after mating; hence the name widow. She stores sperm to produce more egg sacs without mating again. She may live more than 3 years. Spiderlings disperse almost immediately after hatching.

Female widow with egg sac. Row of red dots indicative of Southern Black widow.

Male black widow has proportionately longer legs than female.

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.