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Brown recluse spiders: Facts, bites & symptoms

Brown Recluse Spider_Rick Vetter
A brown recluse spider has only six eyes. (Image credit: Rick Vetter)

The brown recluse spider is well known for its venomous bite. It is the most common and widespread of the brown spiders, but it is usually found only in the South and Central United States.

People bitten by brown recluse spiders should ice the wound and seek emergency medical treatment, as brown recluse bites can cause necrotic (rotting) skin lesions and lead to serious reactions or even death in some people, especially children, according to MedlinePlus (opens in new tab), a service of the National Library of Medicine. But about 90% of brown recluse bites are not medically significant, and they "heal very nicely, often without medical intervention and treatment," Rick Vetter, a retired research associate of entomology at the University of California, Riverside (opens in new tab), wrote on the university's entomology department's website. After seeking emergency help, people with less severe bites usually heal quickly after cleaning the wound and applying the RICE method — rest, ice, compression and elevation — to the affected area, he said. 

Brown recluse spiders (Loxosceles reclusa) are native to a region comprising Kansas, Oklahoma, Texas, Louisiana, Arkansas, Missouri, Mississippi, Alabama and parts of Georgia, Tennessee, Kentucky, Ohio, Indiana, Illinois, Iowa and Nebraska, according to Vetter (opens in new tab). If you do not live in those areas, "it is HIGHLY UNLIKELY that you have a recluse spider," according to Vetter (opens in new tab). "It is POSSIBLE but incredibly unlikely."

This map shows the range of different species of recluse spiders, including the brown recluse (reclusa, in red); Texas recluse (devia, in yellow); Big Bend recluse (blanda, in green); Apache recluse (apachea, in light blue); Arizona recluse (arizonica, in blue); and desert recluse (deserta, in purple). (Image credit: University of California, Riverside)

Appearance: How to identify a brown recluse spider

The brown recluse is part of the Loxosceles genus of spiders. Members of this group have violin-shaped markings on the top of their cephalothorax (fused head and thorax, where the legs are attached) and may be informally referred to as fiddleback or violin spiders, according to Oklahoma State University (opens in new tab).

The brown recluse's violin markings can vary in intensity depending on the age of the spider, with mature spiders typically having dark brown violin shapes. The neck of the violin shape points toward the spider's rear, or bulbous abdomen. However, the violin shape is easy to misinterpret, so it is best to look at the eyes when determining whether a spider is a brown recluse.

The recluse's eyes are one of its most distinctive physical characteristics. "They have six eyes, instead of eight like most spiders," entomologist Christy Bills, the entomology collections manager at the Natural History Museum of Utah, told Live Science. Other types of spiders have eight eyes arranged in rows of four. Recluses, however, have six equal-size eyes arranged in three pairs, called dyads, in a semicircle around the front of the cephalothorax.

Another distinguishing characteristic of the brown recluse spider is its uniformly colored abdomen (though the shade of brown varies from spider to spider) covered in fine hairs, which give it a velvety appearance. Their long, thin legs are also covered in fine hairs, not spines like some non-recluse spiders, Bills said. According to the Integrated Pest Management Program at The University of California, Berkeley (opens in new tab), the scientific name Loxosceles means "slanted legs," and refers to the fact that recluse spiders hold their legs in a slanting position when at rest.

Brown recluse spider bodies (not including their legs) are no more than 0.375 inches (1 centimeter) in length. (Image credit: Oxford University)

The brown recluse's body (not including its legs) is typically between 0.25 and 0.5 inches (0.6 and 1.2 centimeters) long, according to Oklahoma State University.

In short, brown recluses have all five of these features, according to the Integrated Pest Management Program:

  1. Six eyes in dyads (pairs)
  2. Uniformly colored abdomen with fine hairs
  3. No spines on the legs
  4. Uniformly colored legs (no patterns, such as stripes or spots)
  5. Body isn't more than 3/8-inch (1 cm) in length

Classification/taxonomy

According to the Integrated Taxonomic Information System (ITIS), the taxonomy of brown recluse spiders (opens in new tab) is:

  • Kingdom: Animalia
  • Subkingdom: Bilateria
  • Infrakingdom: Protostomia
  • Superphylum: Ecdysozoa
  • Phylum: Arthropoda
  • Subphylum: Chelicerata
  • Class: Euchelicerata
  • Subclass: Arachnida
  • Order: Araneae
  • Family: Sicariidae
  • Genus & species: Loxosceles reclusa

Brown recluse behavior and mating

The brown recluse gets its name from its color and its "shy nature," Bills said. "Most spiders go out of their way to avoid humans, which makes sense, considering we are thousands of times larger than they are and don't have a great record of behaving politely toward them."

These primarily nocturnal spiders build webs that serve as shelters as well as trigger systems, alerting them when prey is passing nearby so they can actively hunt it down, according to the Integrated Pest Management Program. They typically eat insects, such as silverfish and crickets, according to Oklahoma State University. As dawn nears, brown recluses find dark, sheltered hiding places; in nature, they may find refuge in rock cracks and crevices, but if they're near humans, these spiders may camp out in places such as shoes or around human-altered environments, including trash cans, rubber tires or tarps, a quirk that can put them in close contact with people. Male brown recluse spiders may also cross humans' paths when they search for females for mating purposes.

The brown recluse spider is primarily nocturnal.  (Image credit: Image courtesy of the CDC Public Health Image Library)

This is why brown recluse spiders are synanthropic, or found in association with humans, and they are considered "house spiders," according to the Integrated Pest Management Program. 

Brown recluse spiders get around by hitchhiking on furniture boxes and other items from infested structures, according to the Illinois Department of Public Health (opens in new tab). These long-lived spiders, who live an average of 2 to 4 years (opens in new tab) in the wild and up to 7 years in laboratories, have remarkable survival skills, and can go for six to 12 months without eating. Egg laying season lasts from April to July, but a female brown recluse needs to mate only once to produce fertilized eggs throughout her life, and she can produce 150 or more spiderlings in a year and up to five egg sacs in her lifetime. Thus, a single female hitchhiking into a human-made structure is enough to establish an infestation — a fact that may compel people who are moving around or from recluse spider territory to check their belongings before they leave.

Examples of brown recluse spiders living with people

Once established within a structure, brown recluses are often difficult to control. Though hundreds of brown recluses may be present in a house, they may not be easily observed because of their reclusive, nocturnal habits. Therefore, if you see one brown recluse spider, chances are there are more nearby.

Examples of brown recluse populations around human structures include the discovery of 52 spiders at a dilapidated homesite in Mississippi in the early 1970s and 44 caught in sticky traps under a couch in a Tennessee home in just 24 hours, according to the Integrated Pest Management Program. In a wild case, eight 13-year-olds collected about 60 brown recluse spiders from a pile of bricks (the children didn't realize the arachnids were brown recluse spiders) in Oklahoma, but none of the children were bitten.

Even wilder still, a family living in a 19th-century home in Kansas collected 2,055 brown recluse spiders during a six-month period in 2001, according to a study in the Journal of Medical Entomology (opens in new tab). The family had lived in the house for about 10 years, and although they regularly found brown recluse spiders, they only had one instance of getting bitten — when one individual's finger turned red for several days and then healed. "In fact, on many evenings, this family collected more brown recluse spiders per hour in their home than the entire California human population has ever been able to find in the state," according to the Integrated Pest Management Program.

Brown recluse bites and symptoms

Like most spiders, the brown recluse typically only bites when disturbed — though it is possible to inadvertently threaten them. The Texas A&M AgriLife Extension Program (opens in new tab) reports that this may happen if a spider is caught in bedding or clothing.

If the venomous brown recluse bites you, you might not feel a thing, although some people remember feeling a sharp sting, according to MedlinePlus. Bites sometimes, but not always, become painful within a few hours. The reaction the bite causes may range from mild to severe, especially in children.

"People react differently to bites," Bills said. About 10% of brown recluse bites cause moderate or greater tissue damage and scarring, according to Vetter. But the vast majority of bites result in inflammation, can heal without medical intervention and do not leave scars.

After being bitten by a brown recluse spider, a 10-year-old girl in Mexico required two medical procedures to remove blackened, dead tissue from her leg. (Image credit: The New England Journal of Medicine ©2013)

For those with higher sensitivity levels, victims might develop a necrotic lesion that looks like a "dry, sinking bluish patch with irregular edges, a pale center and peripheral redness," Michael F. Potter, an extension entomologist at the University of Kentucky (UK) College of Agriculture, wrote for the UK Entomology Department (opens in new tab). These bites often develop a central blister. If the venom begins to destroy surrounding tissue, the wound may expand several inches over the next few days or weeks. Sometimes, this necrotic ulcer can remain for several months and leave a deep scar, Potter wrote.

According to MedlinePlus, symptoms of a brown recluse bite may include itching, chills, fever, nausea, sweating and a general feeling of discomfort or sickness. More severe symptoms include coma, blood in urine, yellowing of the skin and the whites of the eyes (known as jaundice), kidney failure and seizures.

In rare cases, the bite can cause systemic loxoscelism, a severe illness that involves a blood clotting disorder and destruction of red blood cells, according to a 2017 study in the journal PLOS One (opens in new tab). "Children are much more likely to develop this systemic syndrome," study senior author Dr. Jeremy Warner, a hematologist at Vanderbilt University, said in a statement (opens in new tab). In severe cases, treatment requires hospitalization, blood transfusions and other supportive measures, he said.

Treatment

There is no effective commercial antivenom approved for use in the United States. If you are bitten, MedlinePlus  recommends calling 911 or poison control (1-800-222-1222) or getting to an emergency room immediately.

The NIH says you should wash the area of the bite with soap and water, then wrap ice in a washcloth and place it on the bite area for 10 minutes. Remove the washcloth for 10 minutes, and repeat the process.

Then, go immediately to the emergency room and bring the spider, if possible, for identification purposes.

Brown recluse management

Venomous brown recluses exist within a smaller range than many realize, and their existence may be threatened by climate change. (Image credit: Nick626 via Shutterstock)

To decrease your odds of becoming an unwitting host to these six-eyed spiders, remove or reduce outdoor trash and unneeded outdoor structures, such as wood piles or boxes, especially those near the house, according to the Integrated Pest Management Program. You can also seal cracks around doors, electrical conduits and plumbing fixtures with caulk, expandable foam, weather stripping or other materials to prevent the spiders from entering the house.

If you're in brown recluse territory, move your bed away from the wall, remove bed skirts and clear away items stored under the bed. These moves will reduce the chances that a brown recluse will set up shop around your sleeping area and possibly bite you during the night. Moreover, don't leave clothes and shoes on the floor, or make sure to shake them out before putting them on. Store outdoor equipment, such as gardening gloves and baseball mitts, in tightly sealed bags or bins.

Sticky traps laid down on floor boards are a great non-chemical way to catch brown recluse spiders. Chemical control can be difficult, as these spiders can be challenging to find during the day. If used, liquid, aerosol and dust-based insecticides should be applied to cracks and other places where the spiders might be hiding, Potter wrote for the UK entomology department. Brown recluse fangs are short and can't bite through clothing, so wearing long sleeves, pants and gloves can help protect you when you're working outdoors.

Originally published on Live Science on Nov. 14, 2014 and updated on Feb. 18, 2022.

Additional resources

Watch "How to catch a spider (opens in new tab)" on YouTube that the University of California Statewide Integrated Pest Management Program produced.

Learn more about brown recluse spiders on the Missouri Department of Conservation (opens in new tab) website.

Read about ways to protect yourself from brown recluse spider bites from the Occupational Safety and Health Administration (opens in new tab).

Bibliography

Medline Plus. National Library of Medicine. Brown recluse spider (opens in new tab). Reviewed June 30, 2019.

Rick Vetter. How to Identify and Misidentify a Brown Recluse Spider (opens in new tab). Updated January 2005.

Rick Vetter. Brown Recluse Spider Map (opens in new tab)

Oklahoma State University. Brown Recluse or Fiddleback Spider, Loxosceles reclusa (opens in new tab) 

Rick Vetter. Integrated Pest Management Program at The University of California, Berkeley. Brown Recluse and Other Recluse Spiders (opens in new tab). Revised November 2018.

Integrated Taxonomic Information System - Report. Loxosceles reclusa (opens in new tab). Generated Feb. 16, 2022.

Illinois Department of Public Health. Brown Recluse and Black Widow Spiders (opens in new tab)

Michael F. Potter. University of Kentucky College of Agriculture, Food and Environment. Brown Recluse Spider (opens in new tab). Revised July 12, 2018.

Texas A&M AgriLife Extension. Field Guide to Common Texas Insects: Brown Recluse (opens in new tab)

Robinson, J.R. et al. PLOS One. "Defining the complex phenotype of severe systemic loxoscelism using a large electronic health record cohort (opens in new tab)" (2017)

Laura is the archaeology/history and Life's Little Mysteries editor at Live Science. She also reports on general science, including archaeology and paleontology. Her work has appeared in The New York Times, Scholastic, Popular Science and Spectrum, a site on autism research. She has won multiple awards from the Society of Professional Journalists and the Washington Newspaper Publishers Association for her reporting at a weekly newspaper near Seattle. Laura holds a bachelor's degree in English literature and psychology from Washington University in St. Louis and a master's degree in science writing from NYU.

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