Brown recluse spider

brown recluse spider

The brown recluse spider or violin spiderLoxosceles reclusa, is a well-known member of the family Sicariidae (formerly placed in a family "Loxoscelidae").

Brown recluse spiders are usually between 6–20 mm (¼ in and ¾ in), but may grow larger. While typically light to medium brown, they range in color from cream-colored to dark brown or blackish gray. The cephalothorax and abdomen may not necessarily be the same color. These spiders usually have markings on the dorsal side of their cephalothorax, with a black line coming from it that looks like a violin with the neck of the violin pointing to the rear of the spider, resulting in the nicknames fiddleback spiderbrown fiddler or violin spider.



Since the violin pattern is not diagnostic, and other spiders may have similar markings (such as cellar spiders and pirate spiders), for purposes of identification it is imperative to examine the eyes. Differing from most spiders, which have eight eyes, recluse spiders have six eyes arranged in pairs (dyads) with one median pair and two lateral pairs. Only a few other spiders have three pairs of eyes arranged in this way (e.g., scytodids), and recluses can be distinguished from these as there are no coloration patterns on the abdomen or legs, which lack spines.

The abdomen is covered with bushy short hairs. The leg joints may appear to be a slightly lighter color.


A brown recluse's stance on a flat surface is usually with all legs well extended unless alarmed, when it may withdraw its forward two legs straight rearward into a defensive position, withdraw its rear pair of legs into a position for lunging forward, and raise the pedipalps.

Movement at virtually any speed is an evenly paced gait with legs extended, stopping naturally when renewing its internal hydraulic blood pressure (that, like most spiders, it requires to renew strength in the legs); it then continues at a steady pace until again it needs to renew its blood pressure.

When threatened it usually flees, seemingly to avoid a conflict, and if detained may further avoid contact with fast horizontal rotating movements.


Recluse spiders build irregular webs that frequently include a shelter consisting of disorderly threads. These spiders frequently build their webs in woodpiles and sheds, closets, garages, plenum, cellars and other places that are dry and generally undisturbed. They seem to favor cardboard when dwelling in human residences, possibly because it mimics the rotting tree bark which they inhabit naturally. They also have been encountered in shoes, inside dressers, in bed sheets of infrequently used beds, in stacks or piles of clothes, behind baseboards and pictures, and near sources of warmth when ambient temperatures are lower than usual. Human-recluse contact often is when such isolated spaces are disturbed and the spider feels threatened. Unlike most web weavers, they leave these webs at night to hunt. Males will move around more when hunting, while the female spiders tend to remain nearer to their webs.


The brown recluse spider is native to the United States from the southern Midwest south to the Gulf of Mexico. The native range lies roughly south of a line from southeastern Nebraska through southern Iowa, Illinois, and Indiana to southwestern Ohio. In the southern states, it is native from central Texasto western Georgia and north to Kentucky. A related species, the brown violin spider (Loxosceles rufescens), is found in Hawaii.

Despite many rumors to the contrary, the brown recluse spider has not established itself in California, Florida, or anywhere else outside of the native range. Gertsch and Ennik (1983) report that occasional spiders have been intercepted in various locations where they have no known established populations; Arizona, California, Colorado, Florida, Maine, Minnesota, New Jersey, Mexico, New York, North Carolina, Wyoming and Tamaulipas(Mexico), which indicates that these spiders may indeed be transported fairly easily, though the lack of established populations well outside the natural range also indicates that such movement does not lead to colonization of new areas. There are other species of Loxosceles native to the southwestern part of the United States, including California, that may resemble the brown recluse, but these species have never been documented as medically significant. The number of "false positive" reports based on misidentifications is considerable; in a nationwide study where people submitted spiders that they thought were brown recluses, of 581 from California only 1 was a brown recluse, submitted by a family that moved from Missouri and brought it with them (compared to specimens submitted from Missouri, Kansas, and Oklahoma, where between 75 and 90% were recluses). From this study, the most common spider submitted from California as a brown recluse was in the genus Titiotus, whose bite is harmless. A similar study documented that various arachnids were routinely misidentified by physicians, pest control operators and other non-expert authorities, who told their patients or clients that the spider they had was a brown recluse when in fact it was not. Despite the absence of brown recluses from the Western US, physicians in the region commonly diagnose "recluse bites", leading to the popular misperception that the spiders occur there.

Venomous bite

As indicated by its name, this species is rarely aggressive, and actual brown recluse bites are rare. The spider usually bites only when pressed against the skin, such as when tangled up within clothes, bath towels, or in bedding. Many human victims of brown recluse bites report having been bitten after putting on clothes that had not recently been worn or disturbed. The initial brown recluse bite is frequently not felt and may not even hurt, yet such a bite can be serious nonetheless.

Most bites are minor with no necrosis. However, a small number of bites do produce severe dermonecrotic lesions (i.e., necrosis), and an even smaller number of bites produce severe systemic symptoms. In one study of brown recluse bites, the incidence of skin necrosis was 37% and the incidence of systemic illness was 14%.  In these instances, brown recluse bites produce a range of symptoms known as loxoscelism. There are two types of loxoscelism: cutaneous (i.e., skin) and systemic (viscerocutaneous).

Most brown recluse spiders bites do not result in necrosis, let alone systemic effects. When both types of loxoscelism do result, systemic effects may occur before necrosis, as the venom spreads throughout the body in minutes. Debilitated patients, the elderly, and children may be more susceptible to systemic loxoscelism. The systemic symptoms that are most commonly experienced as the result of a brown recluse bite include nausea, vomiting,fever, rashes, and muscle and joint pain. Rarely, such bites can result in hemolysis, thrombocytopenia, disseminated intravascular coagulation, organ damage, and even death.  Most fatalities are children under the age of seven or those with a weaker-than-normal immune system.

While it is important to note that the majority of brown recluse spider bites do not result in any symptoms, cutaneous symptoms occur as a result of such bites more frequently than systemic symptoms. In such instances, the bite forms a necrotizing ulcer that destroys soft tissue and may take months to heal, leaving deep scars. These bites usually become painful and itchy within 2 to 8 hours, pain and other local effects worsen 12 to 36 hours after the bite, and the necrosis develops over the next few days. Over time, the wound may grow to as large as 25 cm (10 inches) in extreme cases. The damaged tissue becomes gangrenous and eventually sloughs away.

Many necrotic wounds diagnosed as brown recluse bites can actually be methicillin-resistant Staphylococcus aureus (MRSA) or simple staphylococcus infections. Other possible causes of such wounds include skin cancer, Lyme disease, and other infected insect bites and skin lesions.

Numerous other spiders have been associated with necrotic bites in medical literature. Other recluse species, such as the desert recluse (found in the desert southwestern United States), are reported to have caused necrotic bite wounds, though only rarely. Other spiders that have been reported to cause necrotic bites include the hobo spider and the yellow sac spiders. However, the bites from these spiders are not known to produce the severe symptoms that often follow from a recluse spider bite, and the level of danger posed by each has been called into question. So far, no known necrotoxins have been isolated from the venom of any of these spiders, and some arachnologists have disputed the accuracy of many spider identifications carried out by bite victims, family members, medical responders, and other non-experts in arachnology. There have been several studies questioning danger posed by some of these spiders. In these studies, scientists examined case studies of bites in which the spider in question was positively identified by an expert, and found that the incidence of necrotic injury diminished significantly when "questionable" identifications were excluded from the sample set. (For a comparison of the toxicity of several kinds of spider bites, see the list of spiders having medically significant venom.)

Bite treatment

First aid involves the application of an ice pack to control inflammation, the application of aloe vera to soothe and help control the pain, and prompt medical care. If it can be easily captured, the spider should be brought with the patient in a clear, tightly closed container so it may be identified.

There is no established treatment for necrosis. Routine treatment should include elevation and immobilization of the affected limb, application of ice, local wound care, and tetanus prophylaxis. Many other therapies have been used with varying degrees of success including hyperbaric oxygen,dapsone, antihistamines (e.g., cyproheptadine), antibiotics, dextran, glucocorticoids, vasodilators, heparin, nitroglycerin, electric shock, curettage,surgical excision, and antivenom. None of these treatments have been subjected to randomized controlled trials to conclusively show benefit. In almost all cases, bites are self-limited and typically heal without any medical intervention.

It is important to seek medical treatment if a brown recluse bite is suspected, as in the rare cases of necrosis the effects can quickly spread, particularly when the venom reaches a blood vessel. Cases of brown recluse venom traveling along a limb through a vein or artery are rare, but the resulting mortification of the tissue can affect an area as large as several inches, to the extreme of requiring excising of the wound.

Specific treatments

In presumed cases of recluse bites, dapsone is often used effectively for the treatment of necrosis, but controlled clinical trials do not demonstrate similar effectiveness; however, dapsone may be effective at treating many "spider bites" because many such cases are actually misdiagnosed microbial infections. There have been conflicting reports about its efficacy and some have suggested it should no longer be used routinely, if at all.

Wound infection is rare. Antibiotics are not recommended unless there is a credible diagnosis of infection.

Studies have shown surgical intervention is ineffective and may worsen outcome. Excision may delay wound healing, cause abscesses, and lead to objectionable scarring.

Anecdotal evidence suggests benefit can be gained with the application of nitroglycerin patches. The brown recluse venom is a vasoconstrictor, and nitroglycerin causes vasodilation, allowing the venom to be diluted into the bloodstream, and fresh blood to flow to the wound. Theoretically this prevents necrosis, as vasoconstriction may contribute to necrosis. However, one scientific animal study found no benefit in preventing necrosis, with results showing it increased inflammation and it caused symptoms of systemic envenoming. The authors concluded the results of the study did not support the use of topical nitroglycerin in brown recluse envenoming. 

Antivenom, available in South America for the venom of other species of recluse spiders, appears to be the most promising therapy. However, antivenoms are most effective if given early and because of the painless bite patients do not often present until 24 or more hours after the event, possibly limiting the effect of this intervention.


It is estimated that 80% of reported brown recluse bites may be misdiagnosed. The misdiagnosis of a wound as a brown recluse bite could delay proper treatment of serious diseases.There is now an ELISA-based test for brown recluse venom that can determine if a wound is a brown recluse bite, although it is not commercially available and not in routine use.

There are numerous documented infectious and noninfectious conditions (including pyoderma gangrenosum, bacterial infections by Staphylococcus and Streptococcus, herpes, diabetic ulcer, fungal infections, chemical burns, toxicodendron dermatitis, squamous cell carcinoma, localized vasculitis, syphilis, toxic epidermal necrolysis, sporotrichosis, and Lyme disease) that produce wounds that have been initially misdiagnosed as recluse bites by medical professionals; many of these conditions are far more common and more likely to be the source of mysterious necrotic wounds, even in areas where recluses actually occur. The most important of these is methicillin-resistant Staphylococcus aureus ("MRSA"), a bacterium whose necrotic lesions are very similar to those induced by recluse bites, and which can be lethal if left untreated; misdiagnoses of MRSA as "spider bites" are extremely common (nearly 30% of patients later documented to have MRSA initially reported that they suspected a spider bite), and can have fatal consequences. In addition, published work has shown that tick-induced Lyme disease rashes are often misidentified as brown recluse spider bites.

Reported cases of bites occur primarily in Arkansas, Texas, Kansas, Missouri, Colorado, Nebraska and Oklahoma. There have been many reports of brown recluse bites in California(though a few related species may be found there, none of which has been shown to bite humans) and elsewhere outside the range of the brown recluse. To date, the reports of bites from areas outside of the spider's native range have been either unverified, or—if verified—specimens moved by travelers or commerce. Many arachnologists believe that many bites attributed to the brown recluse in the West Coast are not spider bites at all, or possibly instead the bites of other spider species; for example, the bite of the hobo spider has been reported to produce similar symptoms, and is found in the northwestern United States and southern British Columbia. However, the toxicity of the hobo spider itself has been called into question as bites have not been proven to cause necrosis, and the spider is not considered a problem in Europe.


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