Many species of spiders are common household inhabitants in the United States. Certain common house hold spiders spin webs over lamps, in corners, and in basements. This is unsightly but causes no real harm. Remember that every “cobweb” was made by a spider. Although all spiders use venom when they bite and kill their prey, the black widow, hobo, and brown recluse spiders (none of which create cobwebs indoors) are the North American species well documented as dangerous to humans. The agrarian sac spider also is documented to cause painful bites redness, swelling and itching–and occasionally a necrotic wound similar to those caused by the brown recluse. Even though is generally little danger of complications from spider bits, pest management professionals should all spider bite victims to take the spider specimen with them (if possible) when consulting their physician.
Under most conditions outdoors, spiders are considered beneficial because they feed on insects. However, they are undesirable to most homeowners when indoors, and the unsightly webbing spiders use to catch insect prey usually outweighs this beneficial behavior.
The black widow spider, Latrodectus mactans (Fabricius), is widely distributed over the warmer portions of the United States. Females are usually identified because of their globular, shiny black abdomen with two reddish or yellowish triangles on the underside. These reddish or yellowish triangles form a characteristic hourglass marking. The abdomen is about 1/4 inch in diameter but may be as large as 1/2 inch when the female is full of eggs. Males are much smaller and lighter colored, with light streaks on their abdomens.
The black widow’s web is an irregular mass of fibers with a small central area to which the spider retreats while waiting until its prey becomes ensnared. These webs are frequently constructed underneath boards, stones, or the seats of outdoor privies. They are also found along foundation slabs, behind shrubs, and especially where brick or wood siding extends close to ground level. This spider does not usually enter residences, though it may do so occasionally.
Black widow spider venom contains toxins that are neurotoxic (toxic to the nervous system). The severity of a person’s reaction to the bite depends on the area of the body where the bite occurs; the person’s size and general sensitivity; the amount of venom injected; the depth of the bit; the seasonal changes in venom potency; and the temperature. The bite produces a sharp pain similar to a needle puncture, which usually disappears rapidly. After a variety of other symptoms, convulsions and death may result with some victims, especially if the person is sensitive to the venom and no treatment is received. An antivenom specific for the black widow is readily available to most physicians.
The brown recluse spider, Loxosceles reclusa (Gertsch & Muliak), can also inflict a dangerous bite. The initial pain associated with the bite is not intense and is generally less troublesome than a bee sting. Within 8 to 12 hours the pain become quite intense, and over a period of a few days a large ulcerous sore forms. This sore heals very slowly and often leaves an ugly and disfiguring scar.
The brown recluse is a soft-bodied and secretive species found in homes and other outbuildings. The adult varies from 1/3 to 1/2 inch in length, with the arrangement of the legs producing a larger overall size of 1 inch in diameter or greater. The body is yellow to dark brown and has a rather distinctive darker brown violin-shaped mark on the top of the cephalothorax, and a distinctive eye pattern.