Brown Recluse (Loxosceles reclusa): Facts, Range and Venom

What does a brown recluse look like?

The brown recluse is light to medium brown, although individuals range from cream to dark brown. The front part of the body, the cephalothorax, carries a darker violin-shaped mark, with the neck of the violin pointing back toward the abdomen. This mark gives the spider its nicknames, fiddleback, brown fiddler and violin spider.

The most reliable feature is the eyes. Most spiders have eight eyes, but recluses have six, arranged in three pairs: one pair at the front and one pair on each side, forming a shallow U. The abdomen is evenly colored and covered in fine, short hairs, with no stripes or spots. The long, slender legs are also a single color and have no thick spines or bands.

Males and females look much alike. Males have slightly smaller bodies and relatively longer legs, and adult males carry enlarged, dark palps, the leg-like feelers beside the jaws, which they use in mating. A detailed identification guide is in what does a brown recluse look like?

How big is a brown recluse?

Most adults have a body about 6–13 mm (0.25–0.5 in) long, typically around 9 mm (3/8 in), not counting the legs. With legs extended, a large recluse is roughly the size of a coin. Some references quote body lengths up to about 20 mm (0.8 in), but recluse specialists note that a spider with a body clearly longer than about 13 mm (1/2 in) is very unlikely to be a brown recluse.

Spider weights are rarely measured, but even a large female weighs only a small fraction of a gram.

Habitat and range

The brown recluse lives in the south-central and lower Midwestern United States. Its documented range lies roughly south of a line from southeastern Nebraska through southern Iowa, Illinois and Indiana to southwestern Ohio, and from central Texas east to western Georgia. Missouri, Kansas, Oklahoma, Arkansas, Tennessee and Kentucky lie in the heart of its range.

Outdoors it hides under rocks, loose bark, logs and debris in dry, sheltered spots. It also thrives in buildings, where it settles in closets, attics, crawlspaces, basements, garages, barns and sheds, and especially among stored cardboard boxes, which may resemble the bark it shelters under in the wild.

Single spiders are sometimes carried far outside the native range in boxes and furniture, but they have not formed spreading populations elsewhere. Brown recluses are not established in California, the Pacific Northwest, New England, most of the East Coast or Canada. The details, and why so many people believe they have recluses at home, are covered in where do brown recluse spiders live?

Diet and hunting

The brown recluse is a carnivore that feeds on small insects and other arthropods, such as crickets, cockroaches, silverfish and other spiders. It is active at night. Rather than building a large capture web, it spins a small, messy retreat of irregular threads in a hidden corner and wanders out after dark to search for prey.

Females tend to stay close to their retreats, while males roam more widely. Laboratory experiments have shown that brown recluses readily scavenge dead insects, which may help them survive in buildings where live prey is scarce.

They are famously hardy. Brown recluses can survive roughly 6–12 months without food and can tolerate long periods without water, which explains how they persist in dusty attics and storage rooms for years.

Behavior

As its name suggests, the brown recluse is a recluse. It spends the day hidden in its retreat and avoids light and open spaces. When disturbed, it usually runs away. A cornered spider may raise its front legs and palps, freeze or even play dead, and it bites only as a last resort.

The spider’s fangs are short, and it cannot bite through most fabric. Nearly all bites happen when a spider is pressed against bare skin: inside a shoe, glove or piece of clothing that has been left on the floor, in bedding, or when someone reaches into a box without looking.

Brown recluses do not “balloon”, the habit of young spiders of many species to drift on the wind on strands of silk. This is one reason their range has stayed so stable, because young spiders can only walk to new places or be carried by people.

Venom and bites

Like all recluse spiders, the brown recluse has venom containing an enzyme called sphingomyelinase D, which can destroy cells and tissue around a bite. A single bite injects only a tiny amount, at most about a tenth of a microliter.

Most bites are minor and heal by themselves within about a week. Specialists estimate that only about 10% cause moderate or worse skin damage, in which a sunken sore of dead skin forms over several days and can take weeks or months to heal, sometimes leaving a scar. Rarely, the venom causes illness throughout the body, with fever, rash and damage to red blood cells, and this is more likely in young children. Deaths are extremely rare.

Anyone who develops a spreading wound, fever or feels unwell after a suspected bite should get medical care, and anyone with severe symptoms should seek emergency medical help immediately: call 911 in the US. A full, calm look at the risk is in how dangerous is a brown recluse?

Reproduction and life cycle

Mating takes place in the warmer months, from spring to late summer. A male courts a female cautiously, signaling his presence before approaching, and transfers sperm with his palps. The sexes usually part peacefully.

From about May to July, a female produces several round, off-white egg sacs over two to three months, each holding roughly 40–50 eggs, which she guards in her retreat. The eggs hatch in about a month. The spiderlings molt several times and take about a year to reach adulthood. Their shed skins, which look like pale ghost spiders, are often the first sign that recluses live in a building.

Brown recluses usually live 2–4 years in total, and some laboratory spiders have lived more than 7 years. If a recluse loses a leg in a struggle, it does not regrow it with later molts, unlike many other spiders.

Predators and conservation status

Brown recluses are eaten by other spiders, including other recluses when food is short, and by centipedes and other small predators. To escape an attacker, a recluse can shed a leg that has been seized, a defense called autotomy.

The species has not been assessed by the IUCN, so its official status is Not Evaluated. It is common within its range, and in favorable buildings populations can be very dense: entomologists have collected dozens in a single barn in an hour.

Related recluses in North America and Europe

There are more than 100 recluse species worldwide, mostly in warm parts of the Americas, Africa and the Mediterranean. The United States has about eleven native recluses. Besides the brown recluse, most live in the deserts and dry hills of the Southwest, such as the desert recluse (Loxosceles deserta) of California, Arizona and Nevada, and they rarely meet people.

Two recluses have been introduced to the US. The Mediterranean recluse (Loxosceles rufescens) is native to the Mediterranean region, including southern Europe, and has been carried by trade to many countries; in North America it is usually found in isolated populations inside single buildings. The Chilean recluse (Loxosceles laeta) of South America, considered the most dangerous recluse, has small populations in parts of Los Angeles County. Neither the brown recluse nor any other recluse is native to northern Europe or the UK.

Myths and facts

“Brown recluses are everywhere in the US.” They are not. A nationwide study in which people mailed in spiders they believed were brown recluses received nearly 600 specimens from California, and only one was a brown recluse, brought by a family that had moved from Missouri.

“Any brown spider with a violin mark is a recluse.” Many harmless spiders, including cellar spiders and some funnel weavers, have markings that look like a violin. The six-eye pattern and plain, spineless legs are far more reliable. Wolf spiders are among the spiders most often confused with recluses; see the Carolina wolf spider.

“A sore that rots the skin must be a recluse bite.” Many wounds blamed on recluses are bacterial infections, including MRSA, or other conditions. Doctors have even diagnosed “recluse bites” in places where no recluse spiders live.

Relationship with people

Few spiders have shaped medical folklore as strongly as the brown recluse. Loxoscelism, the medical name for the effects of recluse bites, was first described in the United States in 1879 in Tennessee. Since then the spider has been blamed for countless wounds, many of which it did not cause.

Research led by arachnologists such as Richard Vetter of the University of California, Riverside, has done much to correct the picture. The best-known case is a house in Kansas where a family collected 2,055 brown recluses over six months in 2001, after living with the spiders for years, without any serious bites. Studies like this show that the brown recluse deserves respect but not fear. It is one of only two spider groups of real medical importance in the US, alongside the widow spiders; see venomous spiders in the US.