The body of the female adult black widow spider can reach 1 1/2 inches with the legs fully extended. Female black widows are easy to recognize from their shiny black, globular bodies and the distinctive red hourglass shape on their underside. The black widow appears shiny and hairless to the naked eye. The widow spiders are primarily nocturnal, preferring to hide during daylight hours. Black widows build haphazard, tangled webs of impressively strong silk.
Utah Black widow spiders prefer dry dark locations and will seek warm dwellings in winter. In nature, black widows build their webs on rocky outcroppings, under logs, and between stones, rock crevices and under loose bark and stones, in small trees and under bushes. Amidst human habitation, they typically hide in sheltered, dimly lit locations such as garages, dark corners, basements, closets, and cluttered areas.
Black widow spiders are formidable predators that feed on live insects, other spiders and arthropods, as well as on other members of their species.
Life Cycle & Reproduction
Black widows mate and spin egg sacs mostly during the warmer months. A female will produce 5 to 10 egg sacs in her lifetime. Each egg sac will have between 150 and 250 eggs. The eggs hatch in the egg sac and the spiderlings go through a molt before emerging about four weeks later. The newly freed spiderlings are cannibalistic and usually disperse quickly by ballooning (a process in which spiderlings elevate their abdomen and play out silk until their buoyancy is enough to carry them off on the air currents). Spiderlings at this stage can slip through window screening with ease. The small spiderlings are harmless to humans. The female black widow spider lives an average of one year, although some species can live up to three years in favorable environmental conditions. When black widow spider eggs hatch, spiderlings find sheltered hiding places to survive the winter. When warm weather returns, they finish developing into adults.
The female black widow spider is the most venomous spider in North America. Her tiny droplets of poison put both the rattlesnake and the scorpion to shame. Male and juvenile widows, however, pose no threat to humans. The venom of the female black widow spider is a neurotoxin. Muscle and chest pain or tightness are a few of the most common reactions to the widow toxin. The pain also may spread to the abdomen, producing cramping and nausea. Other general symptoms include: restlessness, anxiety, breathing and speech difficulty, and sweating. Often there is a general sense of discomfort shortly after the bite, and acute symptoms increase in severity. Symptoms usually decline after two to three days but some mild symptoms may continue for several weeks after recovery. The very old, very young and those with a history of high blood pressure (hypertensive) are at greatest risk. Prompt medical treatment can greatly reduce the danger from widow bites and has reduced fatalities to extremely low rates in recent years.