Geography – Range

Black Widow spiders inhabit most of the warmer regions of the world to a latitude of about 45 degrees N. and S. They occur throughout all four deserts of the American Southwest.

New Video on the Black Widow spider

Related Species

Widow spiders (Genus Latrodectus) are the best known and largest of the Cobweb Weavers (Family Therididae). All widows are venomous, though not all can cause injury to humans. Black Widows comprise about six species and inhabit most of the warmer regions of the world to a latitude of about 45 degrees N. The female black widow spider, though it is the most venomous spider in North America, seldom causes death as it injects a very small amount of poison when it bites. Reports indicate human mortality at well less than 1% from black widow spider bites. Anyone bitten by a black widow spider should seek medical care; an attempt should be made to catch the spider for identification.

The species L. hesperus is common in the western US and is the Black Widow found in the North American deserts. L. mactans is the Black Widow common in the eastern and central US. The Brown Widow Spider, L. geometricus, is also found in the US.

• L. mactans is found in most warm areas of the world
  
• L. geometricus is found in Africa
  
• L. curacaviensis in the Americas
  
• L. hystrix, L. dahli, and L. pallidus are found in southern Europe,
  northern Africa, and southwestern Asia
  

Comparisons

The Brown Widow Spider (Latrodectus geometricus) is not as dangerous as some other widow spiders because the Brown Widow Spider is less likely to bite someone, and injects less poison. Still, it is a venomous creature, and must be treated with respect. It is found throughout the world's tropical regions, and has been introduced into southern Texas and central and southern Florida.

Hundreds of Australians are bitten every year by the Red-back Spider (Latrodectus hasselti) a close relative of the Black Widow Spider. The Red-back is found in all parts of Australia except in the hottest deserts and on the coldest mountains.

Description

The female Black Widow is shiny black, usually with a reddish hourglass shape on the underside of her spherical abdomen. Her body is about .5 inches long, 1.5 inches when the legs are spread. Adult males are harmless to humans, about half the female's size, with smaller bodies, and longer legs and usually have yellow and red bands and spots over the back as do the immature stages.

Newly hatched spiderlings are predominately white or yellowish-white, gradually acquiring more black and varying amounts of red and white with each molt. Juveniles of both sexes resemble the male and are harmless to humans.

Behavior

Both Western and Eastern Black Widows spin webs that lack shape and form. Their webs are erratic in appearance, and the silk is stronger than almost all other arachnids. The webs are rough and sticky. The black widow spider is shy and nocturnal in habit, usually staying hidden in her web, hanging belly upward. Although not aggressive, she may rush out and bite when her web is disturbed or when accidentally

Habitat

On the underside of ledges, rocks, plants and debris, wherever a web can be strung. Cold weather and drought may drive these spiders into buildings.

Food & Hunting

Like most arachnids, the Black Widow preys on insects. Prey caught in the web include a variety of insects (cockroaches and beetles) and other arthropods. After ensnaring its prey in the web, the Black Widow makes small punctures in the victim's body and sucks out the liquid contents. The Black Widow is preyed upon by Mud-Dauber wasps.

Breeding

Adult male Black Widows wander in search of females but do not feed or bite. Females may occasionally kill and eat a male after mating but this is more the exception than the rule.

The female then lays several batches, containing up to 750 eggs each, in one summer. The egg case, about 1/2 inch in diameter, is suspended in the web. It is white to tan in color and has a paper-like texture. There may be 4 to 9 egg sacs produced during a summer. Normally, only 1 to 12 young survive after the egg incubation period of 14 to 30 days due to cannibalism.

The young Black Widows are colored orange and white when they emerge 1 to 4 weeks later. The female Black Widow may live for more than a year and a half. Growth requires 2 to 4 months, depending on availability of prey during which the females molt 6 to 8 times and the males 3 to 6 times. Females mature about 90 days after egg sac emergence and live another 6 months to a year. Males mature about 70 days after emergence and live only another month or two.

Caution - Venomous!

The venom of the female black widow spider is 15 times as toxic as the venom of the Prairie Rattlesnake. Only a minute amount of the toxin is injected in a single bite by the spider however, so they are rarely fatal. By comparison, the relatively large amount of injected rattlesnake venom results in about 15 to 25 percent mortality among those bitten.

The bite itself is often not painful and may go unnoticed. But the poison injected by the the Black Widow bite can cause abdominal pain similar to appendicitis as well as pain to muscles or the soles of the feet. Other symptoms include alternating salivation and dry-mouth, paralysis of the diaphragm, profuse sweating and swollen eyelids.

Persons with heart conditions or other health problems may require a hospital stay. (Heart and lung failure may result in death.) A physician can evaluate the severity of the bite, and give specific antivenin or calcium gluconate to relieve pain if necessary. Healthy people recover rapidly in two to five days.

First aid measures: Apply an ice pack over the bite location and keep the affected limb elevated to about heart level. Try to collect the spider specimen in a small jar or plastic bag for examination by a spider expert, even if you have crushed it. Treatment in a medical facility may be necessary. Call the Poison Center for additional information. Poison Centers across the country now have a new national emergency phone number - 1-800-222-1222

Be very careful when working around areas where black widow spiders may be established. Take proper precautions - wear gloves and pay attention to where you are working. The reaction to a Black Widow bite can be painful. The victim should go to the doctor immediately for treatment.

To control the black widow, carefully remove all materials where they might hide. They can be cleaned out of an area simply by knocking down the webs, spiders, and round, tan egg sacs with a stick and crushing them underfoot. Removal or destruction of the egg sacks may help control the population. This spider is resistant to many insecticides.

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