Black Widow Spider
Latrodectus mactans (Fabricius), Theridiidae, ARANEAE


DESCRIPTION

Adult -- Like all spiders, the black widow has 8 legs; however, males and females differ in appearance. Females are about 40 mm long with legs outstretched and have black, globular abdomens about 9 by 13 mm marked with a red or yellow hourglass shape underneath. Males are lighter in color and have a red or pale brown stripe down the middle of their backs from which white or yellow streaks radiate. Males are smaller (up to 30 mm long with legs outstretched). The male pedipalps (biting appendages at front of head) are noticeably swollen.

Egg -- Eggs are incorporated into grayish, silken balls about 12 to 15 mm in diameter. These egg masses contain 200 to 900 eggs and are found in the spider's web.

Nymph -- Entirely white at first, nymphs develop through five to eight instars. As they develop, nymphs become more similar in appearance to adult males, though smaller.


BIOLOGY

Distribution -- Though more abundant in the southern states, the black widow spider occurs throughout most of the Western Hemisphere. This species may hide in sheltered, dimly lit places such as barns, garages, basements, outdoor toilets, hollow stumps, rodent holes, trash, brush, and dense vegetation. Black widows usually seek dry, sheltered sites such as buildings during periods of cold weather.

Feeding Habits -- This spider feeds primarily on insects and other arthropods but, when disturbed, it may bite people or animals.

Damage -- The female black widow possesses a venom 15 times more potent than rattlesnake venom. The bite is like a pin prick but causes pain within a few minutes of the attack. The pain spreads rapidly to arms, legs, chest, back, and abdomen. Chills, vomiting, difficult respiration, profuse perspiration, delirium, partial paralysis, violent abdominal cramps and spasms may occur within a few hours of the bite. The victim usually recovers in 2 to 5 days; about 5% of all black widow attacks are fatal. The black widow, however, usually bites people only when its web is disturbed. Male black widows do not bite.

Life History -- The black widow spider overwinters as a young adult in buildings or in sheltered places outdoors. In late spring, after a prolonged courtship, mating occurs. Soon afterward the female kills her mate and begins laying eggs. The grayish silken ball of eggs is attached to an irregular, tangled web with a funnel-shaped exit. Each female constructs 5 to 15 egg balls, each of which contains 200 to 900 eggs.

Young spiders emerge from the ball in 10 to 30 days. They are cannibalistic at this stage. Only a few nymphs from each egg mass survive. They require 2 to 3 months to develop into adults. Older adults die the same summer or autumn after laying eggs. The new generation of adults survives through the winter.


CONTROL

Indoors, spiders and their webs can be vacuumed up without hazard. Outdoors and in outbuildings, caution must be used to avoid being bitten. In fields of fruit or vegetable crops where these spiders are known to be a problem, gloves should be worn as a safeguard against being bitten. Black widow spiders can also be killed with pesticidal sprays.