Brown Recluse Spider: How to Identify It and Its Bite

Count the eyes, not the violin. UC IPM is explicit that the violin marking is unreliable for identification and that the diagnostic feature is the eye arrangement: recluse spiders have six eyes arranged in pairs in a semicircle, while most spiders have eight.

University of Kentucky entomology fills in the rest. An adult with its legs extended is about the size of a U.S. quarter. Colour ranges from tan to dark brown. There is a dark violin-shaped mark on the back with the neck of the violin pointing toward the rear, and the legs are long and thin with no stripes, bands or mottling. That last detail rules out a lot of harmless household spiders, many of which have patterned or banded legs.

Photograph the spider from above and from the front and the app identifies it.

University of Kentucky entomology places the brown recluse throughout the south central and Midwestern United States, and says it is rare outside its native range. UC IPM adds the negative case for the west coast: the brown recluse does not occur in California, specimens occasionally arrive in household goods, and there are no breeding populations in the state.

Within its range it lives up to the name. Indoors it uses crevices behind beds and furniture, closets, shoes, clothing, baseboards, suspended ceilings, wall voids, ducts and registers. Outdoors it is found in barns, sheds and woodpiles, and commonly behind shutters.

That habitat list is also a bite-avoidance list: shake out stored clothing and shoes, and wear gloves when moving woodpiles or cardboard that has sat undisturbed.

The bite is described as painless at first. University of Kentucky entomology says symptoms emerge 3 to 8 hours later, when the site may become red, swollen and tender. A serious reaction takes the form of a dry, sinking bluish patch that may expand up to several inches over a period of days or weeks.

The same source gives the reassuring half of the picture: most bites heal within 3 weeks without serious complication, although ulcers can persist for months. Its advice for a suspected bite is to apply ice, elevate the affected area, and seek medical attention immediately.

Hold both halves together. A slow-healing wound is a reason to be seen by a clinician; it is not by itself evidence that a recluse was involved, particularly outside the spider's range.

UC IPM states that people and their physicians often blame spiders as the cause of skin lesions with no proof of spider involvement, when there are many similar-appearing, non-spider maladies. Combine that with the range information — rare outside the south central and Midwestern states, absent as a breeding population from California — and a reported recluse bite in, say, Oregon or Maine deserves a second look.

University of Kentucky entomology's guide to unexplained bites asks the deciding question: has anyone actually seen or captured a spider? If not, and a careful inspection finds nothing, the person should be referred to a dermatologist. Penn State Extension is blunt about the next step too: do not apply insecticides to your household items, pets or yourself before you know what is going on.

• Catch or photograph the spider if you safely can; a specimen settles the question that a photo of a wound cannot
• Wash the bite and apply ice, ice water or cold compresses (UC IPM); elevate the area (University of Kentucky)
• Seek medical attention immediately for a suspected recluse bite, and for any unusual or severe reaction such as increasing pain or extreme swelling
• In the United States, Poison Help on 1-800-222-1222 is free, confidential and open 24 hours a day
• Mark the edge of any redness with a pen and note the time, so a clinician can see whether it is spreading

This page reports what entomology and IPM sources say. It is not a diagnosis, and no app or web page can tell you what caused a wound on your skin. Compare with black widow identification.

To identify a brown recluse, check its eyes first and then confirm with its legs, abdomen and size. Rick Vetter of the University of California, Riverside's Department of Entomology gives these checks:

• Eyes: six eyes in pairs, one pair at the front and one pair on each side. Most spiders have eight eyes in two rows.
• Legs: uniformly light-coloured, with no stripes and no bands.
• Leg texture: no spines, only fine hairs.
• Abdomen: one uniform colour. A recluse abdomen never has two colours of pigment at once, so spots, stripes or chevrons rule it out.
• Size: about 3/8 inch in body length and not larger than 1/2 inch. Leg span does not count.
• Web: small retreat webs behind objects, never out in the open.

Vetter treats the violin mark as unreliable for non-experts, because people read violins into many other markings. His last test is geographic: if you do not live inside the recluse range, it is highly unlikely the spider is a recluse. Penn State Extension lists 16 states where the species is established: Alabama, Arkansas, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Nebraska, Ohio, Oklahoma, Tennessee and Texas.

According to Vetter, the spiders people most often send in as "recluses" are cellar spiders, funnel weavers, orb weavers and huntsman spiders. Each fails the checks above: they have more than one colour on the legs or abdomen, or visible spines on the legs. University of Kentucky entomologists add wolf spiders, which have banding on the legs.

• Cellar spider: a small, thin body on very long, thin legs, almost always found in its messy cobweb (Kentucky)
• Funnel weaver or grass spider: stripes behind the head and a sheet web leading to a funnel (University of Minnesota Extension)
• Wolf spider: banded legs and a body up to 1 inch long, running on the floor (Kentucky, Minnesota)
• Huntsman spider: visible spines on the legs (UC Riverside)

Compare them on the spider identification page.

Rarer than most people think, even where the spiders are common. In a study reported by the University of California, Riverside, a family in a 19th-century house in Lenexa, Kansas collected 2,055 brown recluses between June and November 2001, and none of the four family members was bitten. The same report contrasts California, where only 8 brown recluses were documented in three years, with 120 bite diagnoses there over the same three years.

When a bite does happen, most are minor. Penn State Extension says about 90 percent of brown recluse bites cause no reaction or a small red bump of about 5 millimetres that heals on its own, and about 10 percent produce a wound with dead tissue. A Kansas State University entomologist describes the usual circumstances: you generally have to brush against one, or have one fall on you, before it bites.

Indoors, all year. University of Kentucky entomologists say brown recluses withstand winter in unheated basements and summer heat in attics, hunt at night and spend daylight hours in dark, secluded places. Penn State Extension says mating happens in June or July, after which the female lays 20 to 50 eggs in a round case; laboratory-raised spiders can live two to three years. America's Poison Centers treats the brown recluse as a summer concern in the Midwest and South.

Sources describe a range, not a single picture. Most bites stay small (Penn State). When a reaction develops, the University of Kentucky describes redness, swelling and tenderness 3 to 8 hours after an initially painless bite. America's Poison Centers describes pain or itching around the site and a bull's-eye or target-shaped lesion, and warns that the blister can turn black as skin tissue dies. It also lists fever, chills, nausea, vomiting, bleeding problems and dark urine within 24 hours as signs of a severe whole-body reaction, which needs emergency care.

No web page or photo can tell you whether a wound on your skin came from a recluse. See a clinician for any bite that is spreading, darkening or ulcerating, and call Poison Help on 1-800-222-1222 in the United States for advice.

The measures sources recommend are mostly about not giving the spider a place to hide next to you:

• Place glue traps widely; University of Kentucky entomologists suggest dozens around a home, which also shows where the spiders are concentrated
• Reduce clutter, which leaves fewer hiding places (Kentucky)
• Move beds away from walls and remove bed skirts so nothing connects the bed to the floor (Kentucky)
• Shake out items that have been in storage and check bedding before getting in (America's Poison Centers)
• Wear gloves when moving firewood, boxes or other stored materials, and do not stack wood against the house (America's Poison Centers)
• Seal cracks and holes in the building's exterior (Kentucky)

Kentucky also names insecticide dusts as particularly effective in cracks and crevices.

Research and drafting for this page used AI assistance. Every figure, date and quotation was then checked line by line against the sources listed at the bottom of the page, each of which was opened while writing. Nothing here is a diagnosis. If a bite, sting or contact with an insect is followed by trouble breathing, swelling of the face or throat, spreading redness, fever or any symptom that worries you, get medical care; in the United States Poison Help (1-800-222-1222) is free and open 24 hours a day.