Wikijunior:Bugs/Black Widow

What does it look like?

A Black Widow spider

A Black Widow is a shiny black spider. It has an orange or red mark that looks like an hourglass. Its abdomen is shaped like a sphere and has an hourglass mark on the bottom. Often there are just two red marks separated by black. Females sometimes have the hourglass shape on top of the abdomen above the silk-spinning organs (spinnerets). Females are usually about 1-1/2 inches long including their leg span. In areas where grapes grow, females are very small and round. They resemble shiny black or red grapes.

Male Black Widows are much smaller than females. Their bodies are only about 1/4 inch long. They can be either gray or black. They do not have an hourglass mark, but may have red spots on the abdomen.

Black widows are sometimes called “comb-footed” spiders. The bristles on their hind legs are used to cover trapped prey with silk.

Young spiders are called “spiderlings”. They shed their outer covering (exoskeleton) as they grow. Spiderlings are orange, brown, or white at first and get darker each time they shed their skin (molt).

Where does it live?

The Latrodectus genus of Black Widow spiders is found throughout the world, especially where grapes grow. They live in North America, South America, and southern Europe. They are also found in Australia, New Zealand, and South Africa.

Their range in the United States is from Massachusetts to Florida, west to Texas, Oklahoma, Kansas, and California. They are most common in the southern states.

Western Black Widows (Latrodectus hesperus) live in western Canada, the Pacific Northwest of the United States, and Mexico. Southern Black Widows (Latrodectus mactans) are found in warm regions of the United States. Northern Black Widows (Latrodectus variolus) are found from southeast Canada to north Florida.

Outdoors they can be found in dark sheltered places such as fallen branches, piles of wood, and rock piles. Sometimes they live in rodent burrows and hollow tree stumps. Other habitats include garages, outhouses, sheds, and basements.

A Black Widow Spider with the remains of her prey.

What does it eat?

Black Widow spiders usually eat small insects such as mosquitoes, grasshoppers, and beetles. They sometimes eat mice, lizards, and snakes caught in the web.

In hot dry places Black Widows are “specialist” feeders, living on a diet of scorpions. When a Black Widow spider bites, the venom subdues the prey. The prey is bathed with digestive fluids. The softer parts dissolve to a liquid that is sucked into the spider’s stomach. The spider’s pincer-like appendages (chelicerae) can be used to puncture the exoskeleton of hard-bodied insects to get the juices. The shell is discarded afterward.

To catch prey, black widows build a “tangle” web. There are three distinct levels: supporting threads at the top, tangle threads in the middle, and vertical trap threads at the bottom. The trap threads are beaded with sticky droplets and attached to the ground. The black widow usually hangs upside down near the middle of the web. When a crawling insect breaks the ground attachment, the web lifts it up toward the waiting spider. Before the insect can get loose, the spider bites it and wraps it in silk.

How does it defend itself?

The Black Widow’s red or orange markings warn predators of danger. It is very quick and is able to detect small vibrations made by a predator. If threatened, it escapes down to the ground on a silk safety line. When disturbed, it often pretends to be dead.

Black Widows use venom to protect themselves. When fangs enter skin, they remain for several seconds. The venom glands are squeezed to deliver the poison through ducts in the fangs.

A female black widow guards an egg sac.

What stages of metamorphosis does it go through?

The Southern Black Widow typically mates during the spring and summer. The female produces an egg mass containing about 200 eggs. She covers it with silk then shapes it into a sac that protects the eggs. The sac is suspended in a web to keep it away from predators. Eggs take about two weeks to hatch. Very few of the young spiders survive because they eat each other as soon as they emerge.

Spiderlings molt several times before reaching adulthood. Diet and temperature are factors that influence development. It takes 2 to 4 months for females to mature. They live about 1-1/2 years. Males mature in 2 to 4 months and live about 4 months.

What special behavior does it exhibit?

Although its bite is dangerous, a Black Widow spider is usually very timid. It may bite if accidentally pressed against the body. If not guarding eggs, it will attempt to escape rather than bite.

Females are said to eat males after mating, so are called “Black Widows.” This behavior is called “mate cannibalism”. It has mostly been observed in laboratory cages where males could not escape. It has only occasionally been seen in the wild, where it is easier for males to escape.

If small bits of prey are hard to digest, they are not eaten. Sometimes they are hung up in the web like trophies.

How does it affect people?

The species Latrodectus mactans is abundant in California and accounts for about half of the spider bites in the United States. The bite makes a double puncture mark on the skin and is very painful. Female Black Widow venom is very toxic, but a very small amount is injected so people do not usually die. Males reportedly do not bite.

The syndrome resulting from a Black Widow spider bite is known as “latrodectism”. The painful symptoms are felt throughout the body. Doctors refer to these as “systemic” symptoms. Black widow venom is called “neurotoxic” because it affects the nerves. When nerves do not work, muscles cannot move. The body becomes rigid with severe cramps and paralysis. Sometimes the breathing muscles stop working causing suffocation.

Many people dislike spiders. In fairy tales, spiders are usually cast as villains. Some people believe they bring bad luck; others believe they bring good luck. Black widows have been helpful in controlling pests, such as imported fire ants and harvester ants.

Early American frontiersmen were often bitten inside dark outhouses by Latrodectus mactans. The rigid condition of the chest and abdomen caused doctors to misdiagnose the symptoms as perforated appendix.

In the 1600s people of southern Europe danced and raved after being bitten by the Malmignatte species of Black Widow. The movement was said to relieve the painful symptoms. Their antics were called the “tarantella” dance, named after the Taranto region of Italy.

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References

Gertsch, W. (1949). American spiders. New York, NY: D. Van Nostrand Company, Inc.

Hillyard, P. (1994). The book of the spider. New York, NY: Random House.

Milne, L. & Milne, M. (2000). National Audubon Society Field Guide to North American Insects and Spiders. New York, NY: Alfred A Knopf.

Understanding science and nature. Insects and spiders. (1993). Alexandria, VA: Time-Life.

http://animals.nationalgeographic.com/animals/bugs/black-widow-spider/

http://animaldiversity.ummz.umich.edu/accounts/Latrodectus_hesperus/

http://www.burkemuseum.org/spidermyth/myths/blackwidow.html

http://en.wikipedia.org/wiki/Latrodectus

http://entnemdept.ufl.edu/creatures/URBAN/SPIDERS/black_widow_spider.htm