Females: 14-16 mm (1/2 inch) body size (not including legs)
Males: approximately half the size of the female (7-8 mm, ~1/3 inch; not including legs)
The western black widow female's body is about half an inch long. Females have a complete hourglass marking on the underside of the abdomen, which is usually completely black except for a small reddish spot near the tip. As female western black widows grow older, they gradually develop into a shiny black or dark brown, with a bright red or orange hourglass. (Net Ref (1)
The male is less than half the size of the female. Males of the western black widow have three diagonal pale stripes on each side of the abdomen and are usually light brown, whereas males of the other species of Latrodectus are generally black. Mature male western black widows do not drastically change their body coloration and resemble juveniles of both sexes. Yet, like the female, the male’s hourglass becomes brighter in color, usually yellow or orange. (Net Refs (1)
Immatures: Spiderlings of both male and female western black widows have the same coloration. Their topside is olive or gray, with white or yellow stripes. Even as spiderlings, both sexes have the characteristic pattern of two opposing triangles or an hourglass on the underside of their abdomen.
Western black widows live in the warmer western regions of the United States. Their range includes extreme southwestern Canada, south into Mexico along the Pacific coast, and east to Texas, Oklahoma and Kansas. This species can be found in all four of the deserts of the American southwest. (Net Ref (1)
Outdoors, western black widow spiders may be terrestrial or live above the ground. Indoors, they build their webs in undisturbed areas that are not frequented by humans. (Net Ref (1)
) In arid parts of Arizona, this spider inhabits almost every crevice in the soil and its nests are found in cholla cacti and agave plants.
The web is typically a 3-dimensional, unorganized mass of silk spun in a dark crevice or corner. The web is sticky, and very strong. If the web is active (in use), the female will be in or very near the web.
The diet of L. hesperus includes beetles, cockroaches, and flies. Black widows kill by means of very small, hollow fangs through which they inject a poisionous venom into their prey. Black widows make small punctures all over the body of their prey, and then proceed to suck out the liquid contents. Because the black widows only take food in the form of liquid, the insect is not fully digested. However, digestive juices of the spider are injected into the insect prey, helping to make more of the prey item edible to the spider. Black widows leave behind the external skeleton of prey insects. These empty shells can be seen near the spider's web. (Net Ref (3)
The western black widow’s time to maturity varies greatly, since it is dependent on temperature and on the availability of prey.
: Adult male black widows wander around in search of a female. During this time, males do not bite or feed. First, a male black widow spins a very small web, and then he places a drop of sperm on the web or the silk. He then takes the sperm into special receptacles on the ends of his pedipalps. Afterwards, he searches for a female so that he can place the sperm into the female's genital opening. After emerging from the egg sac, males mature faster than females, in just 2–5 months; they die after about a month to two months. (Net Ref (4)
: After the female and male mate in this way, the female lays several bunches of eggs, which contain about 750 eggs. A single bunch of eggs is suspended in a web so that nothing happens to to the eggs before they hatch. A single egg case is about 1 cm in diameter. The egg sac can either be tan or white, and usually has a paper-like texture. Within a given summer, a female may make between 4 and 9 egg sacs. Incubation lasts about 14 days, and the young spiders are cannabalistic. Only one to twelve spiders from an egg sac actually live to be 30 days old. Females mature in 3–8 months and usually live up to a year and a half. (Net Ref (4)
: The eggs hatch within the egg sac and the tiny spiderlings remain inside for a few days. After emerging from the egg sac, the spiderlings stay near their mother’s web for a while. About three weeks after hatching, the surviving spiderlings climb to a high point to find a suitable air current. Then, they spin silk threads to float out on passing breezes. Once they have landed, young black widows find a protected place to build their webs. Over time, they extend their webs to capture progressively larger prey. Most spiderlings survive the winter as immature individuals, and with the arrival of spring, they develop into adults. (Net Ref (1))
: Anyone bitten by a western black widow spider should receive prompt and proper medical treatment. While the black widow is considered the most venomous spider in North America, death from a black widow spider bite is highly unlikely. (Net Ref (1)
For the most part, the black widow's bite may be felt only as a pin prick, during which the spider's fangs inject a minute amount of highly toxic venom under the skin. The severity of the victim's reaction depends on his or her age and health, and on the area of the body that is bitten. Local swelling and redness at the site may be followed in one to three hours by intense spasmodic pain, which can travel throughout the affected limbs and body, settling in the abdomen and back (intense abdominal cramping, described as similar to appendicitis), and can last 48 hours or longer. Elderly patients or young children run a higher risk of severe reactions, but it is rare for bites to result in death; only sixty-three having been reported in the United States between 1950 and 1959 (Miller, 1992). Other symptoms can include nausea and profuse perspiration. If left untreated, tremors, convulsions and unconsciousness may result. When death does occur, it is due to suffocation.
For more general information about the Widow spider, please refer to the Latrodectus genus info page.
If you are bitten by a widow spider:
Contact your physician, hospital or poison center immediately and follow their instructions. Poison Centers across the country now have a new national emergency phone number - 1-800-222-1222.
Collect the spider if possible for identification. Your physician may administer an antivenom treatment and calcium gluconate to alleviate pain, and will probably treat the site with antiseptic to prevent infection.
If you have a heart condition or are otherwise vulnerable, you may require a hospital stay until symptoms subside. Usually bite victims recover fully within two to five days.
Be very careful when working around areas where widow spiders may be established. Take proper precautions-wear gloves and pay attention to where you are working. The reaction to a widow bite can be painful, and the victim should go to the doctor immediately for treatment.
1) Zoo.org Fact Sheets
: A well done, detailed info sheet about the Western Black Widow is contained in a PDF document there titled Spiders of the NW (PDF)
2) Montana State University Extension Service
: General information about spiders found in Montana, including the Northern and Western Black Widow.
3) Univerity of Michigan, Museum of Zoology
: A good, thorough description of the Western Black Widow.
4) Desert USA
- A very good guide for various dangers found within the desert.
5) Rick Vetter's pictorial page at UC Riverside
on identifying Brown widows and separating them from Western black widows.