Control of Brown Recluse Spiders

Brown recluse spider

Brown recluse spider

 

One of the most dreaded household pests in Texas is the brown recluse spider. Unfortunately, the bad reputation of this spider is well deserved, for the bite of brown recluse can be painful and may result in disfiguring skin ulcers, severe pain, and, occasionally, life-threatening complications.

As its name implies, the brown recluse is shy and not naturally aggressive. It is most often found in sites that are rarely disturbed, such as under old boards, in piles of discarded junk, and in seldom-disturbed storage spaces in houses and outbuildings. Indoors, they are most common in cluttered closets, garages, crawl-spaces, and attics.

Brown recluse spiders are hunting spiders and do not seem to spend a great deal of time on webs. When webs are constructed, they are inconspicuous and built in protected sites. Nests serve as a place to lay eggs, and as a retreat. They are usually constructed in dark, out-of-the-way corners, in boxes or under debris. Brown recluse spiders are mostly nocturnal, coming out at night to hunt for their insect prey.

Identification

It’s possible for the non-expert to identify the brown recluse spider. Look for a light brown spider, with slender legs extending over an area about the size of a quarter to a half-dollar. Two characteristics that help distinguish this spider from similar species include the dark violin-shaped marking on the back of the front portion of the body, and the semicircular, paired arrangement of six eyes.

Adult brown recluse spiders are most frequently seen during the spring months. Mating season in Oklahoma, Arkansas, and Texas, lasts from April to early July, during which time female spiders produce up to five egg sacs, containing about 50 eggs each. The length of time required for development to the adult stage is slightly less than a year, and in the laboratory, spiders have been observed to live for up to two and a half years.

Control

Because of the seriousness of a brown recluse bite, the best solution to a household infestation of these spiders is to hire a professional pest control company.  Even for professionals, infestations of the brown recluse can be difficult to control. Look for a reputable company that is willing to take the time to work with you and your infestation. A combination of chemical treatments and vigorous sanitation measures are usually required to significantly reduce or eliminate a well-entrenched brown recluse infestation. Brown recluse spiders can be controlled using a four step, integrated approach:

Sanitation. Unnecessary clutter should be eliminated, spider webs removed from interior and exterior areas, and a thorough vacuuming should be undertaken around, under, and behind furniture. Brown recluse spiders are frequently found in and around boxes stored in closets and attics. Boxes in such places should be taped shut to eliminate potential nesting sites. These actions are best done before your pest control operator comes to treat.

Residual sprays. Liquid insecticide sprays should be applied to the exterior foundation, eaves, closets, storage areas, and rugs, if necessary. Sprays with residual killing activity should be selected.

Residual dusts. Insecticidal dusts should be applied in wall voids, attics, and inaccessible crawl spaces. Dusts penetrate places that cannot be reached by sprays, and often provide longer control. Avoid contaminating belongings in storage areas by covering them with a plastic tarp before you treat.

ULV or Aerosol sprays. An ultra-low volume (ULV) or aerosol treatment with pyrethrins or resmethrin may be a useful final step in a complete spider control program.   Alone, ULV treatments are not very effective in controlling spiders;  however they can kill spiders away from their nests, and encourage others to move and contact surfaces treated with residual sprays and dusts.

Tips for professionsals

Research conducted at Oklahoma State and Texas A&M Universities has confirmed that brown recluse spiders are difficult to kill with most insecticides. Among the various liquid spray formulations, pyrethroid insecticides (e.g., Demand® CS, TalstarOne®, Suspend®, Tempo®, and Demon®) appear to give the best control, compared to older chemicals such as Ficam®, Dursban® and Safrotin®. In one trial, the pyrethroid insecticide bifenthrin (Talstar®) showed no significant repellency to brown recluse adults.

The surface to which sprays are applied affects the duration of killing power. Spray treatments applied to wood and masonite surfaces controlled spiders only up to seven days. Residues on some vinyl surfaces provide good control up to 60 days after treatment.

Tempo® Dust (cyfluthrin), a pyrethroid dust, has been evaluated by Texas A&M University and provided relatively rapid kill of brown recluse spiders under laboratory conditions. Another pyrethroid insecticide, DeltaDust® (deltamethrin), is also available to pest management professionals and is probably also effective against spiders.

For more information

For more information on brown recluse and other spiders, request publication E-408, Spiders.

Author:

Michael Merchant, Urban Entomologist, Texas Texas AgriLife Extension, Dallas
Reviewer: John Jackman, Entomologist, Texas AgriLife Extension, College Station

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