July 28, 2004 | By: Ellen Brightwell
Lexington, Ky.

Spiders may invoke images of eerie webs in basements, attics and abandoned buildings or maybe painful, life-threatening bites. However, most spiders are harmless, beneficial insects that help control other pests.

Kentucky has hundreds of different spider species. About 2,500 species are found in North America. Although spiders can be found in the home all year long, they are more abundant during the warm summer and early fall weather.

"Most spiders are 'accidental visitors' that enter homes and buildings through openings such as doors and windows," said Lee Townsend, Extension entomologist with the University of Kentucky College of Agriculture. "Homes near ideal spider habitats such as a wooded area or those with landscaped or naturalized foundations are more prone to frequent invasions."

Spiders that prefer dark, shaded areas may become established in closets, cellars, basements and attics, or beneath heavy, inaccessible furniture. Other species may live in holes in the ground or beneath rocks or logs.

"Although spiders prey on flies, crickets and other insects, the unsightly webs and fecal spots outweigh their benefits to people who simply do not tolerate them in the home," said Mike Potter, UK Extension entomologist.

Most spiders do not bite unless they are held or trapped. Most spiders also have fangs that are too small or weak to puncture human skin. However, some spiders will bite, creating results similar to a wasp or bee sting. It is possible for a person to have an allergic reaction to the venom spiders produce to kill or paralyze prey or as a defensive measure.

"Routine, thorough cleaning is the most effective way to keep spiders out of your home or office," Potter said. "A vacuum cleaner and broom are useful to remove spiders, their webs and egg sacs. Cleaning also discourages spiders from returning. Spiders like quiet, undisturbed areas so put out the 'unwelcome mat' by reducing clutter in closets, basements, garages and attics."

Since spiders congregate around the outdoor perimeter of buildings, reduce migration indoors by clipping back shrubs, tree branches and vines. A vegetative-free zone reduces moisture around the foundation and siding to make this area less attractive to spiders as well as termites and carpenter ants and help prevent decay. To deter spiders, keep firewood, building materials and debris away from the foundation.

"Applying insecticides as a barrier treatment at the base of the foundation also will reduce spider entry from outdoors," Potter said. "Wettable powder or micro-encapsulated (slow release) formulations are the most effective. Longer-lasting liquids are available from some retail outlets. When applying insecticides, pay close attention to door thresholds and entrances to garages and crawl spaces."

Be sure window screens and door sweeps fit tightly to exclude spiders and other insects. Also clean behind outdoor window shutters. Installing yellow or sodium vapor light bulbs at outside entrances is another way to reduce these crawling visitors because these lights are less attractive to night-flying insects that attract spiders.

County Cooperative Extension offices have publications and other educational materials to help residents make their homes unwelcome to pests.


Writer: Ellen Brightwell 859-257-4736 ext. 257
Sources: Mike Potter 859-257-2398
Lee Townsend 859-257-7455