[Spider Control] Managing the Black Widow Spider

Editor’s Note: The following article was adapted from Techletter, a biweekly publication from Pinto & Associates, Mechanicsville, Md. To subscribe, visit www.techletter.com or call 301/884-3020.

The black widow spider may be our most recognizable pest. It’s found in every state except Alaska. Although there are other shiny black spiders and other similar “widow spiders,” it’s the red hourglass marking that identifies the female black widow.

The male spider and the young spiderlings are marked with red, orange and white. They’re small, inconspicuous and harmless. It’s the mature female whose bite can cause severe illness.

The black widow avoids light and is usually found in dry, undisturbed places outdoors such as in woodpiles, under stacked stones, boards or building materials, in boxes or crates, in trash piles or tree stumps, even in rodent burrows. Favorite places are in man-made outdoor structures such as outhouses, sheds, barns, chicken houses, and under porches, decks or eaves. Black widows may be encountered in outdoor meter boxes and even in rodent bait stations. Indoors, they can be found in crawlspaces and in undisturbed corners of basements or garages. Cold or drought may drive them into buildings.

Like other spiders, the black widow is not aggressive unless disturbed or when guarding her egg sac. But that’s the catch. Because she is so reclusive, hidden away in dark corners and under objects, it’s easy to accidentally “disturb” her.

The female black widow spins an irregularly shaped web with a small central tunnel. She stays in or near her web, usually hanging belly up with her hourglass marking showing. Hanging next to her may be a brown, papery, oval egg sac, about ½ inch long. In colder regions, the spiderlings overwinter after hatching, developing into mature adults the following spring.
 

There are periodic “outbreaks” of black widow spiders in more northern regions. Some years, the numbers are few, while the following year there may be large “blooms” of spiders, apparently due to weather conditions. In southern regions, black widow numbers remain fairly consistent from year to year.

Taming the Widow. The following control guidelines apply to most spider problems, including the black widow. The mechanical control measures can be undertaken by the PMP or the customer.

• First, conduct a thorough inspection to locate spider harborage sites for cleanup or treatment. You’re more apt to find black widows at night when they position themselves in the center of their webs.
• Whenever possible, change the conditions that are attractive to the spiders. In other words, reduce sheltered hiding places for the spiders and reduce the number of spider prey. Wear gloves and long sleeves when working in suspected spider harborage sites.
• To keep spiders out of houses, move firewood and stone debris piles away from the foundation. Elevate these materials off the ground for storage.
• Indoors, reduce clutter in garages and basements. Remove seldom used items such as cardboard boxes, old clothing, etc. Vacuum frequently using a crevice tool.
• Small numbers of black widows are easily destroyed mechanically (without chemicals). Simply swat them with a flyswatter or other long-handled tool. Destroy webs and egg sacs by brushing, hosing or vacuuming.
• Periodically use a garden hose and high pressure to wash down outside harborage areas such as rock piles, under decks and roof overhangs.
• Reduce outdoor lights that attract spider prey.
• Many residual insecticides are labeled for the control of spiders. Treat all harborage sites, especially dark corners. Wettable powders, suspensions, or microencapsulated formulations may provide a longer residual. Insecticide dusts tend to cling to the webs and work well in attics and crawlspaces. Do not treat woodpiles with residuals if the wood will be burned indoors.
• There is an anti-toxin available for black widow bites. If bitten, get medical attention immediately.