Brown Recluse Spider

Loxascelidae, Loxosceles reclusa

The brown recluse spider is the best known of the recluse spider group - one of only three common spider groups in the United States that have venom. (The other two are the black widow and the brown widow.) Various colloquial names for the brown recluse spider are violin spiders, fiddleback spiders, recluse spiders, and brown spiders. However, the hobo spider, wolf spider, and jumping spider can also produce bites that require medical attention.

Identification of the Brown Recluse Spider

• Long thin legs
• Oval shaped abdomen
• 6 eyes in dyads (pairs)
• Uniformly colored abdoment with fine hairs
• No spines on legs
• Legs are uniformly colored
• Light tan to dark brown in color
• Distinct violin-shaped mark on on the back points to the posterior of the spider
• Body not more that 3/8" in length

The brown recluse's six eyes are arranged in pairs in a semi-circular pattern that creates the anterior part of the violin shape, though you would need a good magnifying lens to distinguish them. The tail-end segment of the spider has no markings. A brown spider with markings on the tail end is probably not a brown recluse. Their overall size is 3/8 inch to 1/2 inches long. Brown recluse males are slightly smaller than females.

Where Are Brown Recluse Spiders Found?

Brown recluse spiders are found outside in firewood piles, leaves, or piles of rocks, or indoors in dark closets, shoes, cluttered basements or attics. How do you keep brown recluse spiders out of your home and yard?

Recluse Species and Their Range

There are twelve or thirteen recluse spider species in the United States including the infamous Loxosceles reclusa, the brown recluse, which is most common in the midwestern and south-central states, and the Arizona brown spider, or the desert recluse, which is found in the southwestern desert states.

The violin-like markings on the desert species are less obvious, but the bite, though not usually life-threatening, should be considered dangerous and can lead to severe tissue damage. Recluse spiders have also been reported in areas outside this range, sometimes hitchhiking in luggage or inadvertently sent in packaging.

Common Questions:

• What are the symptoms of a brown recluse spider bite?
• How do you keep brown recluse spiders out of your home and yard?
• Are brown recluse spider bites fatal?

The Name: Brown Recluse

As the name "recluse" suggests, these spiders are shy. They retreat when possible, and prefer dark, undisturbed places near or on the ground for their webs, which are used for nesting, not for trapping prey. In fact, the typical web seen in visible areas such as a wall or eave is most likely not due to a brown recluse, but to other types of spiders that may even pursue the brown recluse as prey. Brown recluse spiders usually live in dense clusters. Usually where one is found, there will be more. They are scavengers, preferring dead prey to live.

The nocturnal brown recluse spiders hunt for insects some distance from their webs. Contact with humans usually occurs because they have taken temporary refuge in clothing or bedding. Items left lying undisturbed on the floor, such as supplies, toys, or clothing, are perfect daytime refuges for these spiders. Such objects should be shaken out thoroughly if they have been on the floor or in a closet for any length of time.

Brown Recluse Links: Overview | Bites | Spider Control

Behavior

Brown recluse spiders like undisturbed places for their webs. They hunt primarily at night and will take refuge during the daytime in clothing and bedding, and are often found in unused closets and storerooms, behind furniture, and in baseboard cracks and crevices. Outside, they can be found in foundation cracks, cracks in the soil, and window wells. The brown recluse spider prefers food such as firebrats, crickets, cockroaches and other soft bodied creatures. Earning their name well, the brown recluse spider ceases its wanderings at first light.

The brown recluse spider is a non-aggressive spider and will only bite when disturbed. Usually, the brown recluse spider bite is not felt at the time of occurrence, and pain sets in from six to eight hours later. A typical bite area may resemble a pimple, pustule or blister formation from six to 12 hours later. The bites are unpleasant, producing an ulcerous wound called a necrotic lesion that turns dark within a day and takes a long time to heal. See Symptoms of brown recluse spider bite and information on how to treat the bite.

Breeding

The female brown recluse spider deposits eggs in off-white silken cases about 1/3 inch in diameter in sheltered, dark areas. Spiderlings emerge in 24-36 days and abandon the egg case. Development is slow, influenced by weather conditions and food availability.

They reach maturity in 10 to 12 months and can survive long periods of time without food or water. Immature spiderlings resemble adult brown recluse spiders but have lighter coloration. Spiderlings will molt several times on their journey to adulthood. Brown recluse spider moltings have a stiff appearance - discovery of this type of spider molting can be a useful indication of a brown recluse infestation. Adult males and females will vary from light tan to dark brown.

Common Questions:

What are the symptoms of a brown recluse spider bite?
How do you keep brown recluse spiders out of your home and yard?
Are brown recluse spider bites fatal?

Sources:

National Library of Medicine EPA

"BROWN RECLUSE SPIDER," Michael F. Potter, Urban Entomologist, University of Kentucky College of Agriculture, Department of Entomology, University of Kentucky

Pest Notes: Brown Recluse and Other Recluse Spiders
UC ANR Publication 7468        
Author: R. S. Vetter, Entomology, UC Riverside

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