Black Widow Spider Facts (Latrodectus mactans)

How to Recognize a Black Widow

The stereotypical black widow is a shiny, round, black spider with a red hourglass mark on its ventral side (belly). Mature female black widows present this appearance. They typically also have a red or orange patch above their spinnerets.

Male black widows are much smaller than females, with elongated purple, gray, or black bodies, white abdominal stripes, and red, yellow, or orange spots. Juvenile females are rounder than males, but display similar coloration and markings. Adult males have bulbous pedipalps, which are appendages near the mouth.

Black widow bodies range from 3 to 13 millimeters in size. Females are 8 to 13 mm, while males are 3 to 6 mm in size. Legs are proportional to the body.

Related widow spiders may be gray, brown, or black, with a variety of patterns. They are also venomous! In general, a widow is a shiny, round, dark-colored spider that tends to hang upside down on the edge of its web.

Habitat

Widow spiders (genus Latrodectus) are found in North America, Africa, and Australia, but the black widow with the hourglass markings (Latrodectus mactans or southern black widow) is only found in the southeastern United States, from Ohio to Texas, and in Hawaii.

The spiders prefer shaded, humid, secluded corners in which to build their webs. The frequent wooded areas, but may be found near buildings under tables and chairs and in crevices. Typically, they don't come indoors because there isn't a ready food source, but they do sometimes occur near windows or toilets.

Mating and Reproduction

The black widow female has a reputation for eating her mate. It is true that sexual cannibalism has been observed in black widows, but the behavior is rare in the wild. Males can detect chemicals in a female's web that indicate whether she has fed recently, so they avoid hungry mates. In captivity, the male can't escape, so he may become his mate's next meal.

A mature male spins a sperm web, deposits semen onto it, and places it on the palpal bulbs of his pedipalps. He inseminates his mate by inserting his palpal bulbs into her spermathecal opening. The female spins a globular silk container for the eggs and guards them until they hatch. She can produce from four to nine egg sacs per summer, each filled with 100 to 400 eggs. The eggs incubate for twenty to thirty days. Only around 30 spiderlings hatch because they cannibalize each other after hatching or may not survive their first molt.

Females live up to three years, but male black widows only live three to four months. The spiders are solitary except for the mating ritual.

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Prey and Enemies

Black widows prefer insects, such as flies and mosquitoes, but will eat other small arthropods and sometimes other spiders. The spider builds an irregular three-dimensional web, which is strong enough to trap a mouse. The spider tends to hang from a corner of its web, coming out to quickly wrap its prey in silk before biting and envenomating it. Black widows hold their prey until the venom takes effect, which takes about 10 minutes. When the prey stops moving, the spider releases digestive enzymes into it and carries it back to its retreat to feed.

Black widow venom is neurotoxic. In humans, the symptoms of a bite are collectively termed latrodectism. In contrast to some spider bites, the black widow bite is immediately painful. The venom contains latrotoxins, smaller toxic polypeptides, adenosine, guanosine, inosine, and 2,4,6-trihydoxypurine. If venom is injected, symptoms include muscle pain, sweating, increased heart rate, abdominal cramps, and muscle spasms. The bite itself is very small and may or may not present redness and swelling.

The praying mantis displays a preference for eating Latrodectus spiders. Other predators include the blue mud dauber (Chalybion californicum), spider wasp (Tastiotenia festiva), centipedes, and other spiders. Parasites that affect black widows include chloropid flies and the scelionid wasp. Black widows compete for territory with other spiders. In California, for example, the black widow is being displaced by its relative, the brown widow (Latrodectus geometricus).

How Dangerous Are Black Widows, Really?

Black widow spiders carry a potent venom that can affect humans, but only mature females have chelicerae (mouthparts) long enough to break human skin.

Males and immature spiders can't bite people or pets. Mature females can bite, but they very rarely do so, typically only biting if they are crushed. Even then, they may deliver a venomless dry bite or a bite with a small amount of venom. The bites are rare because it's metabolically wasteful for a spider to give up the chemical it needs to secure food.

Although about two thousand southern black widow bites are confirmed annually, no deaths have occurred in healthy people. In contrast, other widow spiders do, on rare occasions, cause death. An antivenom is available for confirmed bites, but the widow bite is not lethal, so it is used for pain relief. However, research indicates standard pain relievers are as effective as antivenom for relieving symptoms, which resolve within 3 to 7 days.

Black Widow Spider Fast Facts

Common Name: Black Widow Spider

Scientific Name: Latrodectus mactans

Also Known As: Southern Black Widow, Shoe-Button Spider, or simply Black Widow

Distinguishing Features: Shiny black, brown, gray, or purple spider, with red, orange, white, or no markings. Mature females have a red or orange hourglass on the underside.

Size: 3 to 13 millimeters (females larger than males)

Diet: Insects and other small invertebrates

Lifespan: Females live up to 3 years; Males live 3 to 4 months

Habitat: Southern continental United States and Hawaii

Kingdom: Animalia

Phylum: Arthopoda

Class: Arachnida

Order: Araneae

Family: Theridiidae

Fun Facts: Only mature black widow females can bite. Their bite is painful but nonlethal. Mature female black widows can be identified by their hourglass-shaped marking. In the wild, they rarely eat their mates.

Sources

• Foelix, R. (1982). Biology of Spiders, pp. 162–163. Harvard University.
• Kaston, B. J. (1970). "Comparative biology of American black widow spiders". Transactions of the San Diego Society of Natural History. 16 (3): 33–82.
• Rauber, Albert (1 January 1983). "Black Widow Spider Bites". Clinical Toxicology. 21 (4–5): 473–485. doi:10.3109/15563658308990435
• "Taxon details Latrodectus mactans (Fabricius, 1775)", World Spider Catalog, Natural History Museum Bern.