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Black Widow Spider

Latrodectus mactans

Also Called: Hourglass Spider


Black widow spiders are considered one of the most poisonous spiders in North America. They are also the largest web-spinning spiders. Adult black widow spiders are shiny black with two reddish or yellowish triangles on the abdomen that forms an hourglass shape. Their body is approximately one half inch long and their legs about one half inch long. Adult males are about half the size of the females and have a smaller body with red or yellow bands or streaks on the abdomen and spots over the back. Spiderlings are mostly white or yellowish-white and acquire more black with varying amounts of red and white with each molt. Young black widow spiders resemble the males. Adult males and spiderlings are harmless.


Food


Black widow spiders eat insects that get caught in their web.


Habitat


Black widow spiders live in most warm areas of the world including the Eastern and Central regions of the United States. They spin their webs of coarse silk in dark places, usually near the ground in woodpiles, rubble piles, and under decks and under and around houses and outbuildings. They will occasionally spin their web inside as a result of cold weather.


Predators

Mud-Dauber Wasps are natural predators of black widow spiders. Alternating warm and cold weather in the winter and spring are detrimental to their survival.


Social Structure


Female black widow spiders hang on their webs belly up and rarely leave it. The females are shy and will not voluntarily leave their webs, however, if their web is disturbed they may rush out and bite.


Birth and Offspring

Female black widow spiders will usually eat the male after mating. She only has to mate once because she can store the male’s sperm then fertilize her own eggs as she lays them in the sac. The female lays her eggs in silken cocoons or sacs that are about a ½ inch around and are white, later turning to pale brown. Usually, about 4 to 9 sacs are produced during the summer with between 20 and 900 eggs per sac. The eggs hatch in 14 to 30 days after which only 1 to 12 of them will survive due to cannibalism. The spiderlings leave the web after they have hatched. They mature in 2 to 3 months and, during that time, will molt from 3 to 8 times.