Classification and Range Widow spiders belong in the class of arthropods called Arachnida. They are further classified into the order Araneae, and then into the family Theridiidae. Widow spiders are in the genus Latrodectus. Western black widows live and are sometimes common in the western part of North America. Their range includes extreme southwestern Canada, south into Mexico along the Pacific coast, and east to Texas, Oklahoma and Kansas.

Photo: Ann & Rob Simpson

Western black widows are abundant in regions of Arizona, California, and other westerly locales. In Washington state, they live throughout the Columbia Basin and east of the Cascade Mountains. There are also small populations on some of the San Juan Islands and a very tiny colony of western black widows lives in a special habitat on the west coast of Whidbey Island. Other than specimens transported from elsewhere, there are no confirmed records from the mainland of western Washington; occurrence in the Sequim area is possible but unconfirmed.

Habitat
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.

Physical Description
Black widows have a body length of 5/16–5/8 inch (4–16 mm) and a fully extended leg span as long as 1-9/16 inch (40 mm). The mature adult female weighs between .004–.014 ounces (120–400 mg), while the male weighs just .0003–.0006 ounces (8–18 mg).

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.

As female western black widows grow older, they gradually develop into a shiny black or dark brown, with a bright red or orange hourglass. 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.

Life Span
In the wild: Males are short-lived, just 4–6 months. Females live much longer, 27–31 months.
In captivity: Males up to 2 years; females up to 4 years

Diet
In the wild: Insects and other arthropods. They also eat other small animals that get caught in their webs.
At the zoo: 1 cricket per week

Reproduction
After reaching sexual maturity, a male abandons his home web in search of a female. Arriving at a female’s web, he vibrates his abdomen, sending signals through the web. When he is satisfied that she won’t attack, the male slowly moves towards her. Then, he spins a thin layer of silk around her. If she remains still, he mates with her. After he is finished, he drops out of her web. Contrary to popular belief (and how these spiders were named), the female black widow does not always kill the male after mating. The female only kills the male if she is hungry or he makes an abrupt movement while in her web.

After mating, the female stores the sperm and can fertilize subsequent sets of eggs for the rest of her life. About one month after mating, she starts to create an egg sac. It is spherical or pear-shaped, about 1/2 inch (13 mm) long. The female suspends the egg sac within her web. A female makes 6–21 egg sacs from May through October. The number of eggs per sac ranges from 185–464, with a maximum of around 900. The eggs take 8–30 days to incubate.

Life Cycle
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.

The western black widow’s time to maturity varies greatly, since it is dependent on temperature and on the availability of prey. After emerging from the egg sac, females mature in 3–8 months. Males mature faster than females, in just 2–5 months. Most spiderlings survive the winter as immature individuals, and with the arrival of spring, they develop into adults.

Black widows capture their prey in their web, and then wrap them with silk. However, western black widows have their own predators. Certain types of flies or wasps are egg predators of black widows. Other arthropods, birds, small mammals and certain lizards or snakes also eat black widows.

Where is your Web?
Western black widows build irregular cobwebs that lack a consistent shape or form. In its web, the fine strands of silk are for the widow to walk on, and the sticky strands trap potential prey. At the lower level of the web is a haphazard assortment of trap threads spreading out in all directions. At the ends of each trap thread is a sticky drop of silk. When prey becomes entangled in a trap thread, the trap thread breaks free, sticks to the prey animal and lifts it toward the web.

The Wound of a Widow
While the black widow is considered the most venomous spider in North America, death from a black widow spider bite is highly unlikely. Furthermore, western black widows do not actively hunt humans in order to bite them. Latrodectus bites usually occur when the spider is trapped against human skin or provoked to defend itself. In the United States, no deaths from a widow spider have been documented for more than 20 years. Only the larger immature female and adult female spiders can bite through all layers of human skin and inject enough venom to cause a painful reaction. Juveniles and all ages of male black widows are essentially harmless.

Anyone bitten by a western black widow spider should receive prompt and proper medical treatment. The pain and other symptoms usually reach a peak within 12–48 hours of the bite, and then gradually subside over the next 2–5 days. To facilitate treatment, every effort should be made to capture the offending spider and bring it to the medical center where care is given to the person bitten. This is essential for identification purposes and ensures that the correct type of medical care is provided.

There are several ways to avoid widow spider bites. First, be aware of your surroundings and realize that black widows prefer areas of dimly lit shelter. Second, always wear gloves while working in these areas. Third, wear a long-sleeved shirt and long pants when working in areas of potential black widow habitat. If a black widow falls on the hand or arm, brush it off instead of swatting it.