Black-widow spider
Latrodectus hesperus
Order: Araneae
Family: Theridiidae
Genus: Latrodectus
Adult female black widow spiders are usually black and shiny. They are most commonly recognized by the reddish hourglass shape on the underside of the abdomen. The abdomen is quite round. The western black widow female's body is about 1.25 cm long and has an average total length of about 3.5 cm. Adult males are half the size of females, about 6 mm. Their bodies are smaller, but they have longer legs than the females. The males are mostly brown with a swirled pattern. The male's abdomen usually has red spots along the upper midline and white lines or bars radiating out to the sides. Mature male western black widows do not drastically change their body coloration and resemble juveniles of both sexes. Newly hatched black widows are white, but can sometimes be a yellowish-white. Spiderlings of male and female western black widows have the same coloration, however it is distinctly different. 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 they get older, they slowly turn darker. Mature black widows can vary in the amounts of red and white on their bodies. Spiders have two body parts (cephalothorax and abdomen) eight legs and eight eyes.
Conservation Status: IUCN
Distribution
Widow spiders (genus Latrodectus), have a worldwide distribution. Six species occur in North America. This western species, L. hesperus is found from southern Saskatchewan, Alberta and British Columbia south into Mexico. In western Canada, their range is in the extreme south. In Alberta it is restricted to the prairies. Individuals that turn up in central and northern Alberta have been brought in from elsewhere. On occasion, individuals come in on grapes from California. Western black widows live in the warmer drier western regions of the United States. This species can be found in all four of the deserts of the American southwest. Their range continues south into Mexico along the Pacific coast, and east to Texas, Oklahoma and Kansas. One other species occurs in Canada; the northern black widow (L. various) in southeastern Canada.
Habitat
Outdoors, western black widow spiders may be terrestrial or live above the ground. They can be found in a variety of habitats, usually quiet, secluded locations; outhouses, dumps and woodpiles. They live under ledges, rocks, plants and different types of debris. Webs are built near to the ground. They are sometimes built inside trash cans, piles of trash, as well as under houses.
Indoors, they build their webs in undisturbed areas that are not frequented by humans.
Diet
Western black widows like most arachnids feed primarily on insects. The diet of L. hesperus includes beetles, cockroaches, and flies. Black widows kill insects caught in their webs by means of very small, hollow fangs through which they inject poisonous venom. They make small punctures all over the body of their prey, and then proceed to suck out the liquid contents. Because they only take food in a liquid form, the insect is not fully digested. However, digestive juices of the spider are injected into the prey, helping to make more of the item edible to the spider. They leave behind the external skeleton of prey insects. These empty shells can be seen near the spider's web.
Reproduction
The reproduction process is complex. Adult male black widows wander around in search of a female. He spins a very small special web called a sperm web, and places a drop of sperm on the web (or silk). He then takes the sperm into special receptacles on the ends of his pedipalps (secondary reproductive organs). These are a pair of appendages near the mouth that are modified for various reproductive, predatory, or sensory functions. He then places the sperm into the female's genital opening. After they mate this way, the female spins a soft silk to lay her eggs in. This is then wrapped in a stronger silk and then a water-proof silk. She makes up to three pear-shaped egg cases each containing up to several hundred eggs. A single egg case is about 1 cm in diameter. It can be either tan or white and usually has a paper-like texture. Each case is suspended in a web. Within a given summer, a female may make between four and nine egg sacs. Incubation lasts about 14 days. After hatching, the young spiders quickly disperse. The mortality rate is very high, spiders are cannibalistic. Males mature in 70 or so days, quicker than females. Thereafter, they only live for a month or two. Females take longer to mature, 90 days or so and live longer, approximately one and a half years. Some females have been known to live much longer, up to five years.
Adaptation
Spiders have the wonderful ability to make silk. This is used to create webs and egg sacs. Latrodectus builds her web in dark places near the ground, preferring the sheltered sides of buildings, abandoned rodent holes, or openings in stone outcroppings. She seldom ventures indoors. The web is easily recognized by its tangled appearance, and a series of vertical trap threads extending to the ground. The web silk is extremely strong. Crawling insects getting stuck on the sticky threads are quickly lifted into the web where they're wrapped in layers of silk, injected with venom, and sucked dry. Spiderlings emerging from the egg sac leave the web by a process known as "ballooning". A thread line of silk is released until the drag of the air is strong enough to lift the young spider in the air. Venom used for catching prey and protection is 15 times stronger then the venom of a rattlesnake.
Threats to Survival
Spiders prey on other spiders. There are various parasites and predators of widow spiders in North America. Parasites of the egg sacs include the flightless scelionid wasp Baeus latrodecti, and members of the chloropid fly genus Pseudogaurax. Predators of the adult spiders include a few wasps, most notably the blue mud dauber, Chalybion californicum, and the spider wasp Tastiotenia festiva. Other species will occasionally and opportunistically take widows as prey.
