by Gary Braness, Ph.D
The brown recluse spider, Loxosceles recluse, is the most common and important species of Loxosceles spider in North America. These spiders are most common in the south-central United States (Fig. 1), although they may occur outside this natural range when transported in goods.
// Fig. 1. Distribution of the brown recluse spider.
(Illustration by R. Vetter, University of California-Riverside).
Brown recluse spiders usually have a dark brown violin-shaped marking on the upper portion of their bodies. Sometimes this marking is faded or missing, especially in young spiders. A sure way to identify the brown recluse is to carefully observe the eyes. Brown recluse spiders have six eyes that are paired and arranged in a half circle (Fig. 2).
// Fig. 2. Close-up of the brown recluse spider.
(Photo by J. Castner, University of Florida).
The brown recluse spider is best known for its bite and the ulcerous sore that develops (Fig. 3). The bite itself is usually painless, but after several hours intense pain and inflammation develops around the bite. After a few days, an ulcerous sore may form. This sore may become quite large and extend into underlying tissues. Healing is often a slow process. Seek medical attention if you believe you have been bitten by this spider. No specific anti-venom is available, but other treatments will help in healing. If possible, capture the spider so that a proper identification can be made.
// Fig. 3. Ulcerous sore following the bite of the brown recluse.
Biology and Habits
Brown recluse spiders are long-lived, with a life span of two to four years. They feed on live and dead insects. Male spiders travel a much greater area within structures than females. Brown recluse spiders produce webs that are thin and have no definite pattern. Infestations of brown recluse spiders vary greatly in size. Vetter and Barger (2002) reported that more than 2,000 brown recluse spiders were collected during a six-month period from an older home in Lenexa, Kansas. As part of the same study, 30 spiders were collected from a home in Tulsa, Oklahoma. Amazingly, none of the residents in these homes were bitten by the spiders. Sandidge conducted numerous inspections and identified the top 10 areas where brown recluse spiders are found in homes:
// Near furnace and water heater
// Second floor bedrooms – unoccupied
// Any room without air conditioning or ventilation
// Bathroom – behind toilet or tub
// Near plants
// Basement – under stairs
// Basement – in piles of wood, boxes, carpet, clothing
// Behind entertainment center
The first step in effective management of brown recluse spiders is to conduct a thorough inspection of the property. Focus on likely spider habitats. Sticky traps can be used to locate infestations and aid in control. Wear gloves while conducting the inspection to avoid bites.
Five non-chemical spider-proofing methods have been identified by Hedges (2003):
// Changing exterior lighting
// Eliminating harborages
// Removing spider webs from outside the structure
// Sealing cracks and removing screens
// Improving ventilation in attics and crawlspaces
Other tips for brown recluse spider control include:
// Increase humidity and decrease the temperature inside; brown recluse spiders like it hot & dry
// Set out numerous sticky traps in areas where spiders are found
// Seal boxes of files or other papers with packing tape. Boxes must remain sealed for at least six months to kill spiders inside.
Bayer Environmental Science products are effective against brown recluse spiders. For best results, combine indoor and outdoor treatments using various formulations. Large brown recluse spider populations will require a repeat treatment.
Residual Insecticide Sprays:
Indoors, make spot or crack and crevice treatments with residual insecticides directly to spiders and to entry points such as around water pipes, doors and windows. Treat areas where spiders normally feed or hide, such as baseboards, corners, closets, behind furniture or among stored items. In basements and crawl spaces, apply residual sprays to sill plates and other areas where spiders build their webs.
Outside, make spot treatments directly to spiders and to areas they are likely to occur, such as around windows and doors, near light fixtures, under eaves, under window shutters and in ornamental plants located near the structure. Residual dusts should be applied to cracks or voids that serve as entry ways or harborages for spiders. Brown recluse spiders travel on electrical wires in wall voids. Remove the cover to electrical outlets and apply dust to the void. Dusts are also a good choice for treating outside behind shutters and under siding. In moist areas, use waterproof DeltaDust. Use ULV aerosol products containing pyrethrum in attics or above drop ceilings to get spiders moving and in contact with sticky traps or residual sprays or dusts.
For more information, contact your local Bayer Pest Management & Public Health Representative.
References Hedges, S. 2004. Spiders, pp. 923 - 957. In: Mallis Handbook of Pest Control, 9th Ed. S.A. Hedges and D. Moreland, Eds. GIE Media, Inc., Cleveland, OH. Hedges, S. 2003. Spider-man. PCT 31(8): 64, 65, 68, 73. Vetter, R.S. and D. K. Barger. 2002. An infestation of 2,055 brown recluse spiders (Araneae: Sicariidae) and no envenomations in a Kansas home: implications for bite diagnoses in nonendemic areas. J. Med. Entomol. 39(6): 948-951.