[Pest Profile] Black Widow Spiders

Description

The body of the female black widow spider is about ½-inch long, glossy black with a nearly globe-like abdomen. The abdomen has two triangular red spots on its underside arranged in such a way that the spots look like an hourglass. Males are much smaller than the females, ¼-inch long with a longer, narrower abdomen and somewhat longer legs.

Biology

Black widow spiders lay their eggs in silken sacs that they protect in their nests. The young spiderlings remain in the case until the second molt. They live in the vicinity of the nest for two to three weeks before producing long threads of silk that help them float away, much as kites float. Female spiderlings undergo from four to nine molts before maturing. Development time (i.e., from egg to adult) is approximately one year.

Habits

Black widows are shy, preferring to build their webs in dry, protected locations where their prey is likely to travel. Outdoors they can be found among rocks and wood piles, under decks, in hollow stumps, rodent burrows, beneath benches, etc. The webs, which are irregular in shape and about 1 foot in diameter, are used to trap their insect prey which is then paralyzed by their venom. Females produce a neurotoxin and bite if disturbed or handled roughly.

Control

Areas conducive to spider activity, e.g., dark protected areas that attract insect prey, should be identified. Clutter and debris inside structures and scrap lumber, woodpiles, rocks and other protective outdoor materials should be removed. A vacuum cleaner should be used in order to remove spiders, webs, and egg sacs; the bag should then be sealed immediately and discarded. Outdoor lighting that attracts insects to the structure should be changed. Nonresidual aerosols, mists, and ULV’s that contain a pyrethroid insecticide can be used to kill exposed spiders. Dusting spider webs and leaving them undisturbed for several days is also a successful strategy. Pesticides are more effective in eliminating the spiders’ food, i.e., insects, than killing the spiders.

Up Close

• Spiderlings are mostly orange and white but become increasingly more black as they mature
• The female black widow spider’s abdomen has two triangular red spots on its underside arranged in such a way that the spots look like an hourglass.
• Females live up to three years and males approximately 180 days.
• Black widow spiders prefer basements, crawl spaces, and garages in structures as well as other protected areas such as barns, sheds, meter boxes, brick veneer, pump houses, etc.
• Females often eat the males after mating, thus giving them their rather morbid name.
• Pesticides can be applied as residual sprays or dusts with special emphasis on application into potential or known harborage areas.