Brown Recluse Spider

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Spider Facts

Many different kinds of spiders live around homes and buildings. The vast majority are harmless, and in fact are beneficial, because they prey upon flies, crickets and other insects.

Description and Habits

The brown recluse is about 1/4 to 1/2 inches in body length (most adults are about the size of a United States dime to a US quarter with legs extended). Coloration ranges from tan to dark brown, with the abdomen often darker than the rest of the body.

The feature that most distinguishes the brown recluse from many other harmless spiders is a somewhat darker violin-shaped marking on top of the leg-bearing section of the body. The neck of the violin "silhouette" points towards the rear (abdomen) of the spider.

The brown recluse roams at night seeking its prey. During the day, it hides in dark niches and corners, where it may spin a poorly organized, irregular web. Eggs are deposited in 1/2 inch long off-white silken egg sacs, often appearing flattened beneath and convex above. It is shy and will try to run from a threatening situation but will bite if cornered. People are sometimes bitten while they are asleep because they roll onto a brown recluse spider while it is hunting in the bed. More often the victim is bitten while putting on a shoe or piece of clothing which a spider has selected for its daytime hiding place.

Medical Significance

The bite of the brown recluse is usually painless until 3 to 8 hours later when it may become red, swollen, and tender. Later the area around the bite site may develop into an ulcerous sore from 1/2 to 10 inches in diameter. Healing often requires a month or longer, and the victim may be left with a deep scar. Prompt medical attention can reduce the extent of ulceration and alleviate other complications that may develop. It should be noted that not all brown recluse bites result in ulcerations or scarring.

Control

Eliminating an infestation of brown recluse spiders involves two basic principles:

• altering the environment in and around a building to make it less attractive to spiders; and
• finding and destroying as many spiders as possible.

The following measures can be used to control all spiders, including the brown recluse.

1. Routine, thorough house cleaning is the best way to eliminate spiders and discourage their return. A vacuum cleaner or broom effectively removes spiders, webs, and egg sacs.
2. Spiders prefer quiet, undisturbed areas such as closets, garages, basements, and attics. Reducing clutter in these areas makes them less attractive to spiders.
3. Large numbers of spiders often congregate outdoors around the perimeter of structures. Migration indoors can be reduced by moving firewood, building materials, and debris away from the foundation. Shrubs, vines and tree limbs should be clipped back from the side of the building.
4. Install tight-fitting window screens and door sweeps to exclude spiders and other insects. Inspect and clean behind outdoor window shutters.
5. Consider installing yellow or sodium vapor light bulbs at outside entrances. These lights are less attractive than mercury vapor, fluorescent, or incandescent bulbs to night-flying insects which, in turn, attract spiders.
6. To further reduce spider entry from outdoors, insecticides can be applied as a "barrier treatment" around the base of the foundation. Pay particular attention to door thresholds, garage and crawl space entrances, including foundation vents. Sevin (carbaryl), Ficam (bendiocarb), Dursban (chlorpyrifos), or any of the synthetic pyrethroids are effective, but may need to be reapplied periodically throughout the summer. Wettable powder or microencapsulated, "slow-release" formulations are most effective. Longer-lasting liquid formulations of Dursban can be purchased by homeowners through some lawn and garden shops.

The brown recluse may be found living indoors or outdoors. Thorough inspection of cracks, corners, and other dark, undisturbed areas with a bright flashlight will help determine the location and extent of infestation. Indoors, pay particular attention to basements, attics, crawl spaces, closets, under/behind beds and furniture, inside shoes, boxes of stored items, and between hanging clothing. Brown recluse spiders also may be found living above suspended ceilings, behind baseboards, and inside ductwork or registers.

Another way to detect infestations in these areas is to install glueboards or sticky traps. These devices, designed to capture mice and cockroaches, can be purchased at grocery or farm supply stores. Placed flush along walls and in corners, glueboards and sticky traps are useful monitoring tools and will also capture large numbers of spiders.

Brown recluse spiders also live outdoors in barns, utility sheds, woodpiles, and underneath lumber, rocks, and accumulated debris. To avoid being bitten, wear work gloves when inspecting inside boxes or when moving stored items. Removal of unnecessary clutter is especially helpful in making areas unattractive to these pests.