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BLACK WIDOW SPIDER
Not all widow spiders are black. But in the United States, adult females of the three most common widows are almost always a shiny black. The familiar “hourglass” marking located on the underside of the female’s bulb-shaped abdomen is bright red or red-orange. In northern black widows, the upper and lower halves of the hourglass are separated into two red spots, while the marking on the southern black widow is represented by a single, red, hourglass-shaped mark. There is, however, considerable variation among individual widow spiders. Some have no hourglass markings. Most have a smaller red spot near the tip of the abdomen. There may be a line of red spots on the upper side of the abdomen, and northern widows often have white streaks on the sides of their abdomens.
Adult female widow spiders have bodies up to ½-inch long. Total length of 1 and 1/2 inches. The males and immature females are much smaller, they are gray to brown with spots and stripes of red, orange and/or yellow on the upper surface of their abdomens.
The male black widow is not always eaten by the female after mating. Females can live three or more years. Mating occurs in or near the female’s web which is irregular in shape except for a short funnel-shaped portion in which the female hides. The webs measure about one foot in all directions and are typically found in dark, sheltered spots such as in animal burrows, around the bases of rocks, bushes, woodpiles or around the foundations of structures. Egg sacs are often seen in the webs. The sacs are about the size of a large pea and usually contain more than 200 eggs. The spiderlings that hatch from them disperse to new locations by extruding a long strand of silk that is taken aloft by the wind, a process known as “ballooning” that can transport the baby spider to locations several miles away.
Because of their habit of remaining in webs that are purposely built in out-of-the-way locations, bites from black widows are uncommon. Bites may occur when fingers or toes, for example, are stuck into the spider’s web. But black widows usually prefer to run away rather than stand and fight intruders. Most bites occur when the spider is actually touched or pinned against something.
Male widow spiders are not considered dangerous. The bite of the female black widow is often felt as a sharp pin-prick. The neurotoxic venom typically causes chest pain, muscle tightness and cramping. Pain may spread to the person’s abdomen. Swelling can occur in the extremities but rarely around the bite. Other symptoms have been recorded but are less common. Symptoms usually begin to decline after 48 hours and are gone within five days, but milder symptoms may persist for weeks. The more severe symptoms may not occur, and many people bitten by widow spiders do not require treatment of any kind. Bites very rarely result in death. Children and the infirm are at greatest risk for complications.
Denying spiders a place to build webs can help prevent them from coming in contact with people and pets. Filing holes and voids, sealing cracks and crevices, reducing outdoor lighting (so as not to attract insects on which the spiders feed), keeping vegetation away from structures and disposing of outdoor debris helps make an environment unfavorable to spiders.
Controlling black widow spiders involves inspecting structures and yards for the presence of the spiders and their webs. This is best done at night because black widows hide during the day and hang in their webs at night. Like other cobweb spiders, black widows can be dispatched by vacuuming, if care is taken not to release the spiders when emptying the vacuum cleaner. Smashing them with fly swatters, boards and shoes will work as well, as the spiders are not aggressive and cannot run away fast. Treating them directly with a contact pesticide is another option. Lastly, applications of residual pesticides, such as wettable powders or encapsulates, to crawlspaces and around foundations can also deter these and other types of spiders.
Black widows are found throughout the U.S., but predominantly in the South and West. They are usually found in barns, sheds, stone walls, fences, woodpiles, porch furniture, and other outdoor structures.