By Capt. Stefan Tonsberg, EntomologistOctober 31, 2011
For some, autumn triggers a sort of spider sense. The hair on the back of the neck rises in response to sightings of brazen spiders in the middle of a room, or the sensation of something crawling on your skin. Ultimately, this can conjure the belief that spiders have invaded dwellings and infested belongings. Contributing to the anxiety can be the knowledge of potentially dangerous species known to occur not just in the 20-state area supported by U.S. Army Public Health Command Region--West, but all over the country.
Entomologists at the USAPHC understand that most people are unable to distinguish between harmless and dangerous spiders. As result, these entomologists receive an influx of spider questions, sightings, and identification requests. The most frequently asked questions include, "Is it venomous?" "What happens if it bites me?" and "What kind of bug spray should I use to kill it?"
First, almost all true spiders (order Araneae) are venomous. However, of the more than 40,000 species identified, few (around 25 species) are considered medically significant. Funnel-web weaving spiders like the hobo spider, the giant house spider and the barn funnel weaving spider are frequently encountered in the western United States, and often misidentified. Since these spiders are similar, people fear all of them because they resemble the hobo spider, which some scientists suggest may inflict a serious bite.
Spiders that are commonly found around barracks, homes and buildings in the eastern U.S. during the late summer and early fall include grass spiders, wolf spiders, ground spiders, jumping spiders, orb weaver spiders, cobweb spiders, cellar spiders, sac spiders and two less frequently encountered but medically important species, the black widow and brown recluse spider.
Why does it appear that there are more spiders now all across the country?
Even though it seems that the population has increased, spiders do not come inside for warmth as the temperature starts to drop. Most species found outside are adapted to the conditions and would probably not survive inside. The same can be said for species found inside. The truth is that the autumn time period often coincides with the time when select species reach maturity in their lifecycle. In addition male spiders can exhibit a wandering behavior while in search of a mate.
Although, often feared and unwanted, spiders can in fact be beneficial. Spiders prey on numerous insect pests, as well as other spiders. However, for safety, sanitation, and peace of mind their presence is unwanted inside our living or working environment.
The best prevention is through exclusion and cleaning. This means removing rocks, wood piles, compost piles and other sheltering sites adjacent to the home. Cracks and crevices around the foundation and windows should be sealed with caulk or sealant to avoid the entry of spiders. Furniture or other items brought inside should be cleaned and free of egg sacs or spiders. Make sure all screens and doors to the exterior are sealed tight. Keep crawl spaces free of debris and limit other potential hiding places including basements and other dark storage areas.
Spiders may accumulate in large numbers especially around outdoor light sources, which attract their insect prey. Pesticide application is not recommended as egg sacs may survive initial treatment and residual pesticides are not very effective against returning spiders. Vacuuming can be an effective means of removal, but remember to remove or empty the vacuum cleaner bag. Finally, to ensure safety, wear gloves and use caution when handling boxes or firewood stored for long periods or in basements.
Spiders can also be found where Soldiers are deployed. USAPHC entomologists developed illustrated posters for deployed Soldiers to help identify arachnids of Afghanistan and Iraq and Kuwait. These posters are available to anyone with a military e-mail address at: