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Poisonous Spiders of South Carolina

HGIC 2505

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Almost all spiders are capable of producing venomous bites. However, there are very few species of spiders in the United States and South Carolina that produce harmful bites. The U.S. Public Health Service reports that poisonous bites are a very minor cause of death in the United States. Annually, venomous animals produce death as follows: bees, 12; wasps and other hymenoptera, 10; snakes, 14; spiders, six; and scorpions, one. In South Carolina, the widow spiders (Theridiidae: Lactrodectus species) are of most concern and will be discussed in detail. Two other species, Chirocanthium inclusum (a common running spider) and Argiope aurantia (the black and yellow garden spider), have occasionally been reported as inflicting serious bites in humans. None of these bites produced death or prolonged illness.

Black Widow Spiders

Description: The widow spiders are large with mature females measuring 1½ inches with legs extended. Most people are familiar with the southern black widow (Lactrodectus mactans), a glossy black spider with a complete red hourglass marking on the underside of its abdomen. The northern black widow (Lactrodectus variolus ) has the same general appearance as the southern black widow except that it has a broken hourglass on its underside and a row of red spots running down the top side of its abdomen. In both the southern and northern black widows, the typically red markings may be orange, yellow or rarely white. The smaller male widow spiders can be distinguished from the females by the swollen (knob-like) palpal organs projecting from the front of the head. The widow spiders have eight eyes clustered on the front of the head. Male black widows and immatures pose little health threat.

Southern black widow spider
Clemson University - USDA Cooperative Extension Slide Series

Life History and Nature of Injury: The black widow requires about four months from egg to maturity. The females require six to nine molts (shedding of the skin). Egg laying is restricted to the warm months. The females produce several egg sacs (containing hundreds of eggs) during their one-to two-year life span.

The female black widow usually spins a silken web in protected places such as under stones, house steps, decks, etc. The spider is rarely found inside houses. The widow spider is most apt to bite when her eggs are threatened. The black widow bite produces a sharp pain that may persist for hours. Local muscular cramps may develop. The pain may become severe and spread to the abdomen and be accompanied by weakness and tremor. Spasmodic breathing; a feeble pulse; cold, clammy skin; and delirium may be noted. Intravenous injection of 10% calcium gluconate to relieve the muscle spasms has proven effective. A black widow antiserum is available and is an effective treatment.

Brown Widow Spider

The brown widow spider is found in tropical areas. In the United States it was introduced into Florida and is now found throughout that state. The brown widow’s range has been expanding northward and it has recently become established in parts of South Carolina.

Brown widow spider 
F.J. Santana University of Florida

Description: Brown widow spiders are gray to brown in color with white and black markings on the top surface of their bulbous abdomens. The “hourglass” marking on the under surface of the abdomen is yellow to orange, and the legs have dark bands. This species is found in urban areas and may be encountered around the home including: under roof eves, under railings on porches, in abandoned cars, under unused flower pots, in piles of firewood, and under outdoor chairs.

Habits: The mature female of the brown widow spider is from 1 inch to 1½ inches long (with legs extended) and can live 1 to 2 years. In her lifetime, she can lay 10 to 20 eggs sacs with each sac containing approximately 250 eggs. The egg sac of the brown widow spider is white to tan in color and is covered with pointed projections, much like the seed of a sandspur. The egg sac is ½ inch in diameter and is found attached to the web of the female. The egg sac of the black widow, which is similar in color, has a smooth surface.

Young spiders known as spiderlings hatch in approximately 14 to 21 days but remain inside the egg sac for 4 days to one month. After this time they emerge from the egg sac, molt and begin eating but remain in the nest area for several weeks. Eventually, spiderlings move away from the nest area by “ballooning”: a silk line released by each spiderling into the wind and the spiderling is carried off.

Brown widow egg sac
F.J. Santana University of Florida

Females molt 6 to 9 times before reaching maturity, while the male brown widow molts 3 to 6 times before reaching maturity. Males are much smaller than the female (1/2 to 3/4 inch long, with legs extended), do not live as long as the female, and have not been recorded to bite. All three widow spiders in South Carolina are shy and will try to flee rather than bite a human. Cases of widow bites occur when a spider is pressed against the skin of a person (when putting on clothes or shoes) or when a hand is reached into dark areas where the spider is present. It has been reported that the venom of the brown widow is as toxic as the black widow spider, but they are less likely to bite and do not defend their webs as vigorously as black widows.

Spider Control

Effective spider control requires good sanitation and elimination of insect prey as well as chemical treatment. The following control program is suggested:

• Discourage spiders by destroying webs, egg sacs and spiders by brushing or vacuuming.
• Remove collections of paper, boxes and rubbish piles in the house, attic, storage areas, etc. Elimination of harborage will discourage spiders.
• Maintain household insect control. Lack of food will discourage spiders and force them to move elsewhere. Caulk or seal openings to control both insect and spider entry.
• Use chemical control. Space treatment with aerosols containing pyrethrins, such as Ortho Roach, Ant & Spider Killer, are effective as a fast kill of exposed spiders. Treatment of suspect spider harborage with either esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer Concentrate), cyfluthrin (Bayer Advanced Home Pest Control Indoor & Outdoor Insect Killer), or bifenthrin (Ortho Home Defense Perimeter & Indoor Insect Killer) insecticides can be effective. Insecticide dusts containing deltamethrin (Delta Dust) can be used in void areas, attics, and storage buildings.