Brown recluse spider

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For the spider ranging from southeastern California to western Arizona, see desert recluse. For the spider inhabiting Hawaii, see Mediterranean recluse spider.
Brown recluse spider
Brown Recluse.jpg
Scientific classification e
Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Araneae
Family: Sicariidae
Genus: Loxosceles
Species: L. reclusa
Binomial name
Loxosceles reclusa
Gertsch & Mulaik, 1940
Loxosceles reclusa range.png

The brown recluse spider or fiddleback spider, Loxosceles reclusa, Sicariidae (formerly placed in a family "Loxoscelidae") is a spider with a venomous bite.



The brown recluse.











Despite rumors to the contrary, the brown recluse spider has not established itself in California nor anywhere outside its native range.[5] This directly contradicts 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.[6] Over the last century, occasional spiders have been intercepted in various 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 colonization of new areas, after decades of opportunities.[7][8] Note that the occurrence of brown recluses in a single building (such as a warehouse) outside of the native range is not considered a successful colonization; such single-building populations can occur (e.g., several such cases in Florida[9]), but do not spread, and can be easily eradicated.[10]



Main article: Loxoscelism

As suggested by its specific epithet 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.[14][15] The spider usually bites only when pressed against the skin, such as when tangled within clothes, towels, bedding, inside work gloves, etc. Many human victims report having been bitten after putting on clothes that had not been worn recently, or had been left for many days undisturbed on the floor. However, the fangs of the brown recluse are so tiny they are unable to penetrate most fabric.[16]


Around 49% of brown recluse bites do not result in necrosis or systemic effects. 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, thrombocytopenia, disseminated intravascular coagulation, organ damage, and even death.[19] Most fatalities are in children under the age of seven[20] or those with a weak immune system.



It is estimated that 80% of reported brown recluse bites have been misdiagnosed.[4] There is now 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.[4][17][22]


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.[4] 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.[24] 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.[25]



Bite treatment[edit]



Outpatient palliative care following discharge often consists of a weak-moderate strength opioid (e.g. codeine and 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 and/or spasms have not resolved by this time, a second medical evaluation is generally advised, and differential diagnoses may be considered. Occasionally, an antibiotic is prescribed as well.


Specific treatments[edit]

In presumed cases of recluse bites, dapsone is often used for the treatment of necrosis, but controlled clinical trials have yet to demonstrate efficacy.[34] However, dapsone may be effective in treating many "spider bites" because many such cases are actually misdiagnosed microbial infections.[35] 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.[36]

Wound infection is rare. Antibiotics are not recommended unless there is a credible diagnosis of infection.[37]


Anecdotal evidence suggests that the application of nitroglycerin patches can be beneficial.[39] 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 preventing necrosis (as vasoconstriction may contribute to necrosis). 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. [40]

Antivenom, available in South America for the venom of other species of recluse spiders, appears to be the most promising therapy. They are most effective if given early. 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.[41]

Due to increased fear of these spiders prompted by greater public awareness of their presence in recent years, 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 abilities to maintain homeostasis for several seasons with no food or water and to survive after losing limbs.[42] Additionally, these spiders survive significantly longer in a relatively cool, thermally stable environment.[43]

Brown recluses' abilities to survive starvation and thirst, and the way in which they benefit from the regulated room temperatures of human habitations, make extermination of this species particularly challenging. Typically, pesticide control of spiders is difficult. There are various insecticides available in retail outlets labeled for spider control. However, brown recluses' perched legs allow them to walk over most pesticides, making the use of chemicals to eradicate the spiders impractical and unnecessarily toxic.[42] A 2014 study indicates that fumigation may be more effective than previously believed.[44] Sticky traps placed along floor boards offer a non-insecticidal way to trap spiders as well as provide an idea of population levels in the structure. The most important precaution is to remove and reduce trash and rubbish from your property, such as woodpiles, boxes, plywood, tires, and trash cans—especially if they are stored right next to the house. With attached garages, block off house access by sealing cracks around doors and access holes for electrical conduits or plumbing. In the Midwest, some brown recluse bites occur when a sleeping person rolls over during the night, and the trapped spider bites. In the bedroom, move the bed away from the wall, remove any skirts or ruffles and remove all items stored under it. This minimizes chances that any spider can crawl onto the bed. Do not leave clothes and shoes on the floor, or shake them before dressing if they are left out. Apparel and equipment that is only occasionally worn should be stored in tightly closed plastic bags, especially if stored in the garage or other dark storage areas.


  1. ^ Vetter R; Shay, M; Bitterman, O (1999). "Identifying and misidentifying the brown recluse spider.". Dermatol Online J 5 (2): 7. doi:10.2340/00015555-0082. PMID 10673460. 
  4. ^ a b c d e Swanson D, Vetter R (2005). "Bites of brown recluse spiders and suspected necrotic arachnidism.". N Engl J Med 352 (7): 700–7. doi:10.1056/NEJMra041184. PMID 15716564. 
  6. ^ "1st Thai death from recluse spider". Retrieved 30 September 2014. 
  7. ^ [1] University of Florida Fact Sheet
  13. ^ Vetter, R.S., Cushing, P.E., Crawford, R.L., Royce, L.A. (2003). "Diagnoses of brown recluse spider bites (loxoscelism) greatly outnumber actual verifications of the spider's presence in four western American states". Toxicon 42 (4): 413–418. doi:10.1016/S0041-0101(03)00173-9. PMID 14505942. 
  14. ^ "An Infestation of 2,055 Brown Recluse Spiders (Araneae: Sicariidae) and No Envenomations in a Kansas Home: Implications for Bite Diagnoses in Nonendemic Areas" by Richard S. Vetter and Diane K. Barger, J. Med. Entomol. 39(6): 948Ð951(2002); available online at
  18. ^ "Greta Binford 1997-". Biography Today (Omnigraphics, Inc.) 17 (1): 14. 2007. ISSN 1058-2347. 
  19. ^ Wasserman G (2005). "Bites of the brown recluse spider". N Engl J Med 352 (19): 2029–30; author reply 2029–30. doi:10.1056/NEJM200505123521922. PMID 15892198. 
  20. ^ Tenn. Boy Ruled Killed by Spider Bite - MSNBC Wire Services -[dead link]
  22. ^ Gomez H, Krywko D, Stoecker W (2002). "A new assay for the detection of Loxosceles species (brown recluse) spider venom". Annals of Emergency Medicine 39 (5): 469–74. doi:10.1067/mem.2002.122914. PMC 3201721. PMID 11973553. 
  23. ^ Osterhoudt KC, Zaoutis T, Zorc JJ (2002). "Lyme disease masquerading as brown recluse spider bite". Annals of Emergency Medicine 39 (5): 558–61. doi:10.1067/mem.2002.119509. PMID 11973566. 
  28. ^ Bennett RG, Vetter RS (August 2004). "An approach to spider bites. Erroneous attribution of dermonecrotic lesions to brown recluse or hobo spider bites in Canada". Canadian Family Physician 50 (8): 1098–101. PMC 2214648. PMID 15455808. 
  29. ^ James H. Diaz, MD (April 1, 2005). "Most necrotic ulcers are not spider bites". American Journal of Tropical Medicine and Hygiene 72 (4): 364–367. 
  35. ^ Vetter R, Bush S (2002). "The diagnosis of brown recluse spider bite is overused for dermonecrotic wounds of uncertain etiology". Annals of Emergency Medicine 39 (5): 544–6. doi:10.1067/mem.2002.123594. PMID 11973562. 
  38. ^ Rees R, Altenbern D, Lynch J, King L (1985). "Brown recluse spider bites. A comparison of early surgical excision versus dapsone and delayed surgical excision". Ann Surg 202 (5): 659–63. doi:10.1097/00000658-198511000-00020. PMC 1250983. PMID 4051613. 
  40. ^ Lowry B, Bradfield J, Carroll R, Brewer K, Meggs W (2001). "A controlled trial of topical nitroglycerin in a New Zealand white rabbit model of brown recluse spider envenomation". Annals of Emergency Medicine 37 (2): 161–5. doi:10.1067/mem.2001.113031. PMID 11174233. 
  44. ^ Vetter, Richard S.; Hoddle, Mark S.; Choe, Dong-Hwan; Thoms, Ellen. 2014. Exposure of Brown Recluse and Brown Widow Spiders (Araneae: Sicariidae, Theridiidae) to a Commercial Sulfuryl Fluoride Fumigation. Journal of Economic Entomology 107(5): 1813-1817, DOI:

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