The Black Widow Spider
Excerpt from E-72: Spiders (pdf file), by Ralph E. Williams and Gary W. Bennett, Extension Entomologists
"The female black widow is jet black in color and, with its legs extended, would about cover a penny. The abdomen is spherical and, in the female only, is marked on the underside with a red or yellow “hour glass.” There may be a few red spots also on top of the abdomen.
The poison of the black widow affects the nervous system of humans. Persons bitten may experience a variety of symptoms, such as dizziness, blurred vision, breathing difficulty, nausea and severe pain around the wound. In such instances, a physician should be contacted immediately.
The black widow lives in undisturbed locations, such as under rocks and boards, and in and around old buildings. She is active on her irregular web during the day.
Control: Most spiders can live for several months without food. Therefore, controlling the insects upon which they feed is a very slow control technique.
Sanitation is the most practical method of spider control. Clean away all webbing with a vacuum cleaner so that eggs and spiders are picked up and destroyed. Ordinary housecleaning with a cloth, dust mop, or broom is not effective. Keep premises free of unneeded, undisturbed clothing, papers, and other litter. Many spiders may be excluded from the home by caulking or otherwise eliminating cracks and crevices around the foundation of the house and around windows and doors.
Chemical control using a long-lasting residual spray containing a pyrethroid insecticide is effective when applied around the outside of the home and in undisturbed locations in the house where spiders are likely to be found. Check labels of specific insecticide products for active ingredient listings. Aerosols, mists, or fogs containing synergized pyrethrins or related synthetic pyrethroids can also be used for control indoors where residual sprays are not desirable.
Outside areas usually needing attention are porches, garages, and eaves of the roof. Spiders may also be found in crawl spaces, basements, and unexcavated areas beneath the house. All areas where spiders are found should be treated."