The brown recluse appears to be in great abundance.
Their bites can be mild to serious and occasionally fatal. As of 1984, at least 5 deaths had been reported from their bites in the USA. Their hemolytic venom is dangerous. The toxins in the bite kill the cells surrounding the puncture, producing a black gangrenous spot. Often, the skin proceeds to peel away from the area around the wound, exposing the underlying tissues. In extreme cases, an area 6 inches across can be severely affected and, since the wounds are slow to heal, they leave a very unpleasant scar.
They are our allies in the continuing battles with insects. They help to control many destructive and annoying insects and pests.
They feed largely on insects; they inject prey with venom that is hemolytic rather than neurotoxic. They normally eat at night.
Eastern Texas to western Georgia and north to southern Illinois
Biogeographic Regions: nearctic (Native )
Brown recluse spiders are often found around human habitations, outdoors under rocks and bark as well as indoors in houses, schools, sheds, and barns.
Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest
The brown recluse is about 1/2 inch long. It is brown and bears a violin-shaped dorsal stripe on its cephalothorax.
Other Physical Features: ectothermic ; bilateral symmetry
A courtship usually preceeds the actual mating. A male relies mostly on the fine sensory hairs that cover his body and appendages to locate a female. Along with the sense of touch, a male also has the ability to distinguish various chemical substances. Through this combined chemotactic sense, the male finds his mate by a scent that she leaves on the threads of her web or on any substratum on which she may have moved. The female would be more than likely to view an advancing male as suitable prey if she was not made aware of his presence in some way. So the male must announce himself by certain maneuvers, in which the female may later engage when she has reached a certain pitch of excitement, that are part of the courtship ritual and which, if all goes well, eventually lead to the actual mating. These maneuvres consist of the male signalling his presence by tweaking the threads of the female's snare on her web and maybe by moving his palpi and abdomen in a sort of dance. The male may perform bizarre dances, wave his palpi or legs or both, display his ornaments, and strike peculiar attitudes. If the male is successful in lulling her normal instinct to view him as prey and in stimulating her to a point where sexual union is possible, she submits to his advances and mating takes place. In most cases the sexes separate peaceably. The male may even mate again with the same female or with some other female. The actual mating takes place when the male deposits a drop of sperm on a small web that he spins before mating, and then picks up the sperm and stores it in the special cavities of his pedipalps. He inserts the pedipalps into the female genital opening when he mates to store the sperm in her seminal receptacles. There is usually a courtship ritual before mating. The female lays her eggs in a silken cocoon, which she may carry about or attach to a web or plant. A cocoon may contain hundreds of eggs, which hatch in approximately two weeks. The young usually remain in the egg sac for a few weeks and molt once before leaving it. Several molts occur before adulthood.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate)
At least by name, the Brown Recluse (Loxosceles reclusa) is one of the best known spiders among non-arachnologists. The Brown Recluse is a small, yellowish brown spider with a characteristic darker mark on the carapace, broader at the front and narrowed behind (to some observers, this mark resembles the shape of a violin). Length is around 9 mm for females and 10 mm for males (Kaston 1978). Although this spider is not hard to recognize for those familiar with it, inexperienced observers can easily find other small brown spiders with markings that could conceivably be described similarly. One additional character that is unambiguous is that Loxosceles (and other spiders in the family Sicariidae) have only six eyes (rather than the more common 8), which are arranged in a recurved row (i.e., median eyes farther forward than the laterals) of three pairs (Ubick 2005). Spiders without this distribution of eyes are not Brown Recluses.
Loxosceles spiders are widely known because their bites can cause significant skin necrosis (sometimes referred to as cutaneous loxoscelism) and other serious symptoms--although in the great majority of cases, no serious symptoms develop following a Brown Recluse bite. Loxosceles spiders were not documented in the literature as medically important until the mid-20th century. In North America, once they were determined to be a public health threat, there was great interest in defining the distribution of the Brown Recluse. This was followed by many reports of bites, both verified and unverified, in both the medical and popular literature. Most symptoms attributed by patients to "spider bites" in fact have some other cause. This misattribution of symptoms can have serious medical consequences if it results in delayed or inappropriate treatment. For example, methicillin-resistant Staphylococcus aureus (MRSA) bacterial infections are a potentially very serious cause of skin and soft tissue injury and are often presented by patients as spider bites. Suchard (2011) found that the great majority of patients seeking medical attention for a "spider bite" were actually suffering from skin and soft-tissue infections. Medical professionals also overdiagnose spider bites, with potentially serious consequences (such as failing to diagnose Lyme disease or other pathologies). More accurate diagnosis may sometimes be assisted by an ELISA immunoassay (Gomez et al. 2002; Stoecker et al. 2006).
Of the approximately 100 Loxosceles species, 51 are native to North and Central America and 33 to South America (one, L. rufipes, is shared between the two continents). The Brown Recluse is normally found only in the south-central United States, with several related species in the southwestern United States and southward. Although the general public and many physicians across the United States are quick to attribute mysterious skin lesions or other symptoms to Brown Recluse bites, Vetter (2005) could find no evidence that significant Brown Recluse populations exist outside the central and south-central United States (from southeastern Nebraska through the southernmost strip of Ohio and south into Texas to northern Georgia and western South Carolina), although reports of bites outside this region are not rare. Brown Recluses belong to a group of spiders that does not disperse by ballooning, which may partly explain why local infestations outside the primary range tend not to spread. Other studies have also found a pattern of Brown Recluse bite diagnoses inconsistent with the distribution and abundance of Brown Recluses (Vetter 2009a; Vetter et al. 2003, 2009). In many cases, the spider is never seen and diagnosis is based on poorly interpreted circumstantial evidence; in other cases, medical personnel, pest control operators, and other "authorities" have a specimen, but identify it incorrectly (Vetter 2009b).
Although symptoms from Loxosceles bites are usually mild, they can ulcerate or cause more severe, systemic reactions. These injuries mostly are due to sphingomyelinase D in the spider venom. There is no proven effective therapy for Loxosceles bites, although many therapies are reported in the literature. (Swanson and Vetter 2006) Vetter (2008) reviewed biological, medical, and (interestingly) psychological aspects of envenomation by Brown Recluse spiders and this key reference should be consulted by anyone interested in Brown Recluse (and other Loxosceles) spiders and, in particular, their interactions with humans. Medical aspects have also been reviewed by Swanson and Vetter (2006) and Vetter and Isbister (2008).
Although they do have the potential to be quite serious, bites are uncommon even where Brown Recluses are common. As their name implies, Brown Recluses are reclusive and have a predilection for crevices and other tight locations. In nature, they can be found under rocks and the loose bark of dead trees. In synanthropic environments (i.e. where they cohabit with humans), they are found in cardboard boxes (especially under folded flaps), in cupboards, behind bookcases and dressers, in trash, under broken concrete and asphalt, and (of particular medical concern) in shoes and clothes left out on the floor or stored in closets and garages.
These spiders can be found in very high density in synanthropic situations. A Kansas family collected 2,055 Brown Recluses in their home in the course of 6 months and a survey in Kansas showed that 22 of 25 homes sheltered Brown Recluses, with an average of 83.5 to 114.9 spiders per home (range 1 to 526). In an Oklahoma barn, a team of arachnologists collected 1,150 Brown Recluses over three consecutive nights with an essentially undiminished capture rate, although the size of the spiders decreased slightly as collecting progressed.
Brown Recluses are active hunters that do not make typical webs for prey capture. Instead, theyextend lines of silk from a retreat to opportunistically alert them to the presence of entangled prey. For more information about their biology, see Vetter (2008).
More information about Brown Recluse (and other) spiders is available from the University of California-Riverside Spiders Site.
(Vetter 2008 and references therein)
Despite ongoing claims by the general public, and in some cases medical practitioners, the brown recluse spider does not occur in California. Many years of searching for the spider, including public offerings of rewards, have failed to find the spider in the wild there.
A few specimens have been collected (about 40) in the 100+ years of scientific collecting in California, but they have ALL been associated with boxes or similar items that were recently shipped from locations where the spider occurs.
For additional places the spider does or does not occur, please see the maps associated with this taxon
The brown recluse (Loxosceles reclusa), Sicariidae (formerly placed in a family "Loxoscelidae") is a recluse spider with necrotic venom. Similar to those of other recluse spiders, their bites sometimes require medical attention. The brown recluse is one of three spiders in North America with medically significant venom, the others being the black widow and the Chilean recluse.
Brown recluse spiders are usually between 6 and 20 millimetres (0.24 and 0.79 in), but may grow larger. While typically light to medium brown, they range in color from whitish to dark brown or blackish gray. The cephalothorax and abdomen are not necessarily 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 spider, brown fiddler, or violin spider.[2]
The violin pattern is not a definitive identifier, as other spiders can have similar markings (e.g. cellar spiders and pirate spiders). Instead, while most spiders 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). Recluses have no obvious coloration patterns on the abdomen or legs, and the legs lack spines.[3] The violin marking can vary in intensity depending on the age of the brown recluse spider, with mature spiders typically having dark violin shapes.[4][5]
The documented range of this species 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 Texas to western Georgia and north to Kentucky.[6][7]
Despite rumors to the contrary, the brown recluse spider has not established itself in California or anywhere outside its native range.[8] There are other species of the genus Loxosceles native to the southwestern part of the United States, including California, which may resemble the brown recluse, but interactions between humans and the recluse species in California and the region are rare because those species native ranges lie outside of dense human populations.[8] 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).[9] From this study, the most common spider submitted from California as a brown recluse was in the genus Titiotus, whose bite is deemed 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.[10] Despite the absence of brown recluses from the Western U.S., physicians in the region commonly diagnose "brown recluse bites", leading to the popular misconception that the spiders inhabit those areas.[11]
Over the last century, spiders have occasionally been intercepted in locations where they have no known established populations; these spiders may be transported fairly easily, though the lack of established populations well outside the natural range also indicates that such movement has not led to the colonization of new areas, after decades of opportunities.[12][13] Note that the occurrence of brown recluses in a single building (such as a warehouse) outside of the native range is not considered as successful colonization; such single-building populations can occur (e.g., in several such cases in Florida),[14] but do not spread, and can be easily eradicated.[15] The spider has also received numerous sensationalized media reports of bites occurring where these spiders are absent (and no specimens were found), such as a 2014 report from Thailand, where a man was claimed to have died from a brown recluse bite.[16] Many misidentifications and erroneous geographic records stem from the similarity between L. reclusa and a related introduced species, the Mediterranean recluse (Loxosceles rufescens), which is found worldwide, including numerous sightings throughout the United States; the two species are superficially almost indistinguishable, and misidentifications are common, making it difficult to distinguish which reports of recluses refer to which species.[17]
Adult brown recluse spiders often live about one to two years. Each female produces several egg sacs over a period of two to three months, from May to July, with approximately fifty eggs in each sac. The eggs hatch in about one month. The spiderlings take about one year to grow to adulthood. The brown recluse spider is resilient and can tolerate up to six months of extreme drought and scarcity or absence of food. On one occasion, a brown recluse survived in controlled captivity for over five seasons without any food at all.[18]
As part of the haplogynae, brown recluse do not balloon, which limits its ability to widely disperse geographically.[19] The brown recluse will, though not habitually, cannibalize another if food becomes scarce; especially during its typical mating season from June to September or when an unreceptive female encounters an aggressive male.[20]
A brown recluse's stance on a flat surface is usually with all legs radially extended. When alarmed it may lower its body, withdraw the forward two legs straight rearward into a defensive position, withdraw the rearmost pair of legs into a position for lunging forward, and stand motionless with pedipalps raised. The pedipalps in mature specimens are dark and quite prominent and are normally held horizontally forward. When threatened it usually flees, seemingly to avoid a conflict, and if detained may further avoid contact with quick horizontal rotating movements or even resort to assuming a lifeless pose (playing dead). The spider does not usually jump unless touched brusquely, and even then its avoidance movement is more of a horizontal lunge rather than a vaulting of itself entirely off the surface. When running, the brown recluse does not leave a silk line behind, which would make it more easily tracked when it is being pursued. Movement at virtually any speed is an evenly paced gait with legs extended.
The brown recluse spider displays autotomy as a defense mechanism against physical, predatory attack to a leg as well as to prevent predatory, venom injections from spreading to the rest of the body.[21] "Once a leg is lost, a recluse spider does not regenerate a new one with subsequent molts", unlike the huntsman spider that does regenerate autotomized legs.[21] With each time that a leg is autotomized, the recluse "changes its gait to compensate for the loss."[21]
Brown recluse spiders build asymmetrical (irregular) webs that frequently include a shelter consisting of disorderly threads. They frequently build their webs in woodpiles and sheds, closets, garages, plenum spaces, cellars, and other places that are dry and generally undisturbed. When dwelling in human residences they seem to favor cardboard, possibly because it mimics the rotting tree bark which they inhabit naturally.[22] Human-recluse contact often occurs when such isolated spaces are disturbed and the spider feels threatened. Unlike most web weavers, they leave these lairs at night to hunt. Males move around more when hunting than the females, which tend to remain nearer to their webs.
Loxosceles reclusa (as with all of the Loxosceles genus) can deliver, through envenomation via uncate chelicerae-type fangs, a potentially dermonecrotic[23] loxoscelism[24] due to the presence of sphingomyelinase D[23] toxin in its venom.[25] Most bites are minor with no dermonecrosis. However, a small number of brown recluse bites do produce dermonecrotic loxoscelism; an even smaller number produce severe cutaneous (skin) or viscerocutaneous (systemic) symptoms. In one study of clinically diagnosed brown recluse bites, skin necrosis occurred 37% of the time, while systemic illness occurred 14% of the time.[26] In these cases, the bites produced a range of symptoms common to many members of the genus Loxosceles known as loxoscelism, which may be cutaneous and viscerocutaneous. In very rare cases, bites can even cause hemolysis—the bursting of red blood cells.[27]
As suggested by its specific name reclusa (recluse), the brown recluse spider is rarely aggressive, and bites from the species are uncommon. In 2001, more than 2,000 brown recluse spiders were removed from a heavily infested home in Kansas, yet the four residents who had lived there for years were never harmed by the spiders, despite many encounters with them.[28][29] The spider usually bites only when pressed against the skin, such as when tangled within clothes, shoes, towels, bedding, inside work gloves, etc. Many human victims report having been bitten after putting on clothes or shoes that had not been worn recently or had been left for many days undisturbed on the floor. The fangs of the brown recluse are not large enough to penetrate most fabric.[30]
When both types of loxoscelism do result, systemic effects may occur before necrosis, as the venom spreads throughout the body in minutes. Children, the elderly, and the debilitatingly ill may be more susceptible to systemic loxoscelism. The systemic symptoms most commonly experienced include nausea, vomiting, fever, rashes, and muscle and joint pain. Rarely, such bites can result in hemolysis, low platelet levels, blood clots throughout the body, organ damage, and even death.[31] Most fatalities are in children under the age of seven[32] or those with a weak immune system.
While the majority of brown recluse spider bites do not result in any symptoms, cutaneous symptoms occur more frequently than systemic symptoms. In such instances, the bite forms a necrotizing ulcer as the result of soft tissue destruction 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.[33] Over time, the wound may grow to as large as 25 cm (10 inches). The damaged tissue becomes gangrenous and eventually sloughs away. L. reclusa can produce slightly more than 0.1 microliters of venom, though the average yield is less.[34]
There is an ELISA-based test for brown recluse venom that can determine whether a wound is a brown recluse bite, although it is not commercially available and not in routine clinical use. Clinical diagnoses often use Occam's razor principle in diagnosing bites based on what spiders the patient likely encountered and previous similar diagnoses.[7][26][35]
A mnemonic device, "NOT RECLUSE", has been suggested as a tool to help laymen and medical professionals more objectively screen and diagnose potential cases of loxoscelism.[36]
There are numerous documented infectious and noninfectious conditions that produce wounds that have been initially misdiagnosed as recluse bites by medical professionals, including:
Many of these conditions are far more common and more likely to be the source of necrotic wounds, even in areas where brown recluse spiders actually occur.[7] 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.[38] Misdiagnosis of MRSA as spider bites is extremely common (nearly 30% of patients with MRSA reported that they initially suspected a spider bite), and can have fatal consequences.[39]
Reported cases of brown recluse bites occur primarily in Arkansas, Colorado, Kansas, Missouri, Nebraska, Oklahoma, and Texas. There have been many reports of brown recluse bites in California—though a few related species may be found there, none of these are known to bite humans.[8] To date, the reports of bites from areas outside of the spider's native range have been either unverified or, if verified, the spiders have been moved to those locations by travelers or commerce. Many arachnologists believe that a large number of bites attributed to the brown recluse in the West Coast are either from other spider species or not spider bites at all. For example, the venom of the hobo spider, a common European species established in the northwestern United States and southern British Columbia, has been reported to produce similar symptoms as the brown recluse bite when injected into laboratory rabbits. However, the toxicity of hobo spider venom has been called into question as actual bites have not been shown to cause necrosis, and no such occurrences have ever been reported where the spider is native.[40]
Numerous other spiders have been associated with necrotic bites in the medical literature. Other recluse species, such as the desert recluse (found in the deserts of southwestern United States), are reported to have caused necrotic bite wounds, though only rarely.[41] The hobo spider and the yellow sac spider have also been reported to cause necrotic bites. However, the bites from these spiders are not known to produce the severe symptoms that can follow from a recluse spider bite, and the level of danger posed by these has been called into question.[42][43] So far, no known necrotoxins have been isolated from the venom of any of these spiders, and some arachnologists have disputed the accuracy of spider identifications carried out by bite victims, family members, medical responders, and other non-experts in arachnology. There have been several studies questioning the danger posed by some of these spiders. In these studies, scientists examined case studies of bites in which the spider in question was identified by an expert, and found that the incidence of necrotic injury diminished significantly when "questionable" identifications were excluded from the sample set.[44][45] (For a comparison of the toxicity of several kinds of spider bites, see the list of spiders having medically significant venom.)
First aid involves the application of an ice pack to control inflammation 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.
Routine treatment should include 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.[46][47] In almost all cases, bites are self-limited and typically heal without any medical intervention.[7]
Outpatient palliative care following discharge often consists of a weak or moderate strength opioid (e.g. codeine or tramadol, respectively) depending on pain scores, an anti-inflammatory agent (e.g. naproxen, cortisone), and an antispasmodic (e.g. cyclobenzaprine, diazepam), for a few days to a week. If the pain or spasms have not resolved by this time, a second medical evaluation is generally advised, and differential diagnoses may be considered.
In presumed cases of recluse bites, dapsone is often used for the treatment of necrosis, but controlled clinical trials have yet to demonstrate efficacy.[48] However, dapsone may be effective in treating many "spider bites" because many such cases are actually misdiagnosed microbial infections.[49] There have been conflicting reports about its efficacy in treating brown recluse bites, and some have suggested it should no longer be used routinely, if at all.[50]
Wound infection is rare. Antibiotics are not recommended unless there is a credible diagnosis of infection.[51]
Studies have shown that surgical intervention is ineffective and may worsen outcomes. Excision may delay wound healing, cause abscesses, and lead to scarring.[52]
Purportedly application of nitroglycerin stopped necrosis.[53] However, one scientific animal study found no benefit in preventing necrosis, with the study's results showing it increased inflammation and 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. [54]
Antivenom is available in South America for the venom of related species of recluse spiders. However, the bites, often being painless, usually do not present symptoms until 24 or more hours after the event, possibly limiting the effect of this intervention.[55]
Due to increased fear of these spiders prompted by greater public awareness of their presence in recent years, the extermination of domestic brown recluses is performed frequently in the lower midwestern United States. Brown recluse spiders possess a variety of adaptive abilities, including the ability to survive up to 10 months with no food or water.[56] Additionally, these spiders survive significantly longer in a relatively cool, thermally stable environment.[57]
{{cite journal}}: CS1 maint: unfit URL (link) The brown recluse (Loxosceles reclusa), Sicariidae (formerly placed in a family "Loxoscelidae") is a recluse spider with necrotic venom. Similar to those of other recluse spiders, their bites sometimes require medical attention. The brown recluse is one of three spiders in North America with medically significant venom, the others being the black widow and the Chilean recluse.
Brown recluse spiders are usually between 6 and 20 millimetres (0.24 and 0.79 in), but may grow larger. While typically light to medium brown, they range in color from whitish to dark brown or blackish gray. The cephalothorax and abdomen are not necessarily 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 spider, brown fiddler, or violin spider.
