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Black Widow Spider
HYG-2061A-97
William F. Lyon
Common Name Scientific Name
Black Widow Spider Latrodectus mactans (Fabricius)
Northern Widow Spider Latrodectus variolus (Walckenaer)
Both the black widow spider and northern widow spider are present in Ohio. The black widow spider is found primarily in the southern Ohio counties whereas the northern widow spider is found in the northern Ohio counties. Most occur outdoors and are not aggressive unless confined or disturbed. Females are more likely to bite when guarding an egg sac. Reports indicate that mortality from bites is the result of one percent or less of the cases, usually occurring in very young or very old individuals. With healthy people, recovery is usually complete in 2 to 5 days. However, this spider is considered the most venomous spider in North America.
Identification(Click here for a large color photo)
Adult black widow spiders have shiny, jet black, rounded, globular abdomens with two reddish or yellowish triangles on the underside which form a characteristic hourglass marking. Adult female northern widow spiders are shiny black or brown-black with two reddish triangles on the underside, resembling a split hourglass. These spiders are about 1/2-inch long, not including the legs (about 1-1/2 inches when legs are spread). Adult males are harmless, about half the female's size, with smaller bodies, longer legs and usually have yellow and red bands and spots over the back as do the immature stages. Newly hatched spiderlings are predominately white or yellowish-white, gradually acquiring more black and varying amounts of red and white with each molt. Juveniles of both sexes resemble the male and are harmless.
Life Cycle and Habits
These spiders spin tangled webs of coarse silk in dark places, usually outdoors. Webs are usually built near the ground (occasionally within dwellings) normally in trash, rubble piles, under or around houses and outbuildings such as privies, sheds and garages. The female lays eggs in silken cocoons or sacs which are globular in shape and about 1/2-inch in diameter. Sacs are white at first, later turning pale brown. About 300 to 400 eggs per sac is common with 4 to 9 egg sacs produced during a summer. Normally, only 1 to 12 young survive after the egg incubation period of 14 to 30 days due to cannibalism.
Growth requires 2 to 4 months depending on availability of prey during which the females molt 6 to 8 times and the males 3 to 6 times. Females mature 92 days after egg sac emergence and live about 179 days longer, whereas males mature 71 days after emergence and live 30 days longer. Usually the female eats the male after mating. However, if females are well fed, most males get away to mate another day. Females hang belly upward, rarely leaving the web. Often cold weather and drought may drive these spiders into buildings. Prey caught in the web include a variety of insects (cockroaches and beetles) and other arthropods. The northern widow spider is similar to the black widow except its habitat is marginal land with sparse vegetation. It is found in stumps, hollow logs and piles of debris (occasionally indoors). The female black widow is shy and nocturnal in habit. She does not leave her hidden web voluntarily and is completely out of her area when away from the web. Outbreaks of black widows occur erratically. Some years an area may have thousands of widows and the next year they may be gone. Certain kinds of habitats such as sand dune areas may have black widows every year. Alternating warm and cold weather during the winter and spring months are detrimental to survival.
Bite Symptoms
According to Willia Gertsch, curator of spiders at the American Museum of Natural History, New York, the venom of the black widow spider is 15 times as toxic as the venom of the prairie rattlesnake. However, only a minute amount of the toxin is injected with a single bite by the spider, while the relatively large amount of injected rattlesnake venom results in about 15 to 25 percent mortality among those bitten.
The severity of a person's reaction to the bite depends on the area of the body bitten, amount of venom injected, depth of bite, seasonal changes and temperature. The bite feels like a pin prick or is not even felt. At first, there may be only slight local swelling and two faint red spots surrounded by local redness at the bite. Pain becomes intense in one to three hours and may continue up to 48 hours. Pain usually progresses from the bitten member up or down the arm or leg, finally localizing in the abdomen and back. The abdominal muscles may become rigid and board-like with severe cramps (resembles appendicitis). There may be pain in the muscles and soles of the feet, and eyelids may become swollen. Other symptoms may be nausea, profuse perspiration, tremors, labored breathing and speech, and vomiting. During this time, a feeble pulse, cold clammy skin, unconsciousness, convulsions and even death may result if the victim does not receive medical attention immediately. Additional complications may occur due to the infection of the bite. However, with some untreated individuals, symptoms may diminish in several hours and be gone in several days after agony. Bites are uncommon and serious long-term complications or death are rare. Only four deaths were officially attributed to black widow bites in the United States from 1960-69.
First Aid
If bitten, remain calm, collect the spider, if possible, for positive identification and get medical attention immediately. (Contact your physician, hospital and/or Poison Information Center.) First aid is of limited help. Application of a mild antiseptic such as iodine or hydrogen peroxide prevents infection.
Persons younger than 16 and older than 60, especially those with a heart condition, may require a hospital stay. (Health and lung failure may result in death.) A physician can give specific antivenom or calcium gluconate to relieve pain. Healthy people recover rapidly in two to five days.
Control Measures
The black widow spider is shy and nocturnal in habit, usually staying in her hidden web. Although not aggressive, she may rush out and bite when her web is disturbed or when accidentally trapped in clothing or shoes. Many are associated with dry, undisturbed piles of firewood, old limbs, rock piles, bales of hay, wooden buildings and pit privies.
Prevention
Remove trash, old boxes, piles of lumber, old rubble piles and other unwanted items from under or around houses and outbuildings. Do not go barefoot or handle firewood without gloves. Install screens on doors and windows to prevent entry. Seal or caulk cracks and crevices where spiders can enter the house. Wash off the outside of the house or building, especially around window wells and other undisturbed places where webs are built. Spiders are fragile and easily damaged, so sweeping with a stiff broom will remove webbing and usually kill them. (Use Caution.)
Insecticides
Since black widow spiders spend most of the time in or on webbing, thorough applications of fine particles of insecticides, such as ULV, aerosols or fogs, contact spiders in their webs causing quicker population reduction. Although pyrethrin is registered specifically for black widow spiders, other space sprays of resmethrin (Vectrin) are useful for clean outs in outbuildings, crawl spaces, etc.
There are many other labeled pesticides for spider control. Some are labeled for homeowner use, while others are labeled only for the licensed, certified, pesticide applicator or pest control operator. Homeowners can use amorphous silica gel (Drione, Tri-Die), some formulations of bendiocarb (Ficam), chlorpyrifos (Dursban), and permethrin (Astro, Dragnet, Flee, Prelude, Torpedo); diazinon, esfenvalerate (Conquer), propoxur (Baygon), pyrethrin (Exciter, Kicker, Microcare, Pyrethrum, Safer, Synerold, Uld, X-Clude) plus resmethrin (Vectrin). In addition, the licensed pesticide applicator can use bendiocarb + pyrethrins (Ficam Plus), clyfluthrin (Optem, Tempo), cypermethrin (Cyper-Active, Cynoff, Demon, Vikor), deltamethrin (Delta Dust, Suspend), lambdacyhalothrin (Commodore), propetamphos (Safrotin) and tralmoethrin (Saga).
Residual crack and crevice sprays of Diazinon or propoxur (Baygon) applied where spiders can hide and enter buildings, are helpful.
Outdoors, spray around the perimeter of buildings using formulations that will not damage plants. Treat under patios and decks if the house is of pier and beam construction. Baygon, Diazinon, Drion and Permethrin are frequently used.
Before using any pesticide, always read the label and follow directions and safety precautions.
