As the weather outside turns colder, critters begin seeking warmer shelter in houses, barns, basements, sheds and woodpiles. A most unwelcome guest that appears during this yearly indoor migration is the black widow spider.
The poisonous black widow is common throughout Colorado. Reports indicate that bites result in death for only 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. It is not aggressive and fatalities from its bite are uncommon. However bites can cause serious illness, so precautions are especially in order at this time of year.
The female black widow is poisonous and the male is not. The female is about 1.5 inches long, ,jet black in color and usually has a red hourglass marking on the underside of the abdomen.The male is smaller with brown markings.
This spider is found in undergrowth, under stones, in garages, window wells, crawl spaces and basements. Homes in new developments will be bothered for some time from natural populations in the area.
Black widows spin tangled webs of coarse silk in dark places, usually outdoors. Webs are usually built near the ground (occasionally within dwellings). The female lays eggs in silken cocoons or sacs that 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 are common with 4 to 9 egg sacs produced during a summer.
Normally, only 1 to 12 of the young will survive after the egg incubation period of 14 to 30 days, due to cannibalism.