• Envenomation by bite of brown recluse spider (Loxosceles reclusa) typically resulting in mild local inflammation and less commonly associated with necrotic skin lesions or generalized systemic reaction
  • Also called loxoscelism, fiddleback spider bite, violin spider bite

ICD-9 codes

  • 905.1 spider bite, venomous
  • 989.5 toxic effect of venom


  • Approximately 50 known species of Loxosceles; 11 are found in North America
  • Species reclusa usual cause of human pathology (endemic in south and central United States)


  • Bites uncommon in United States, even in homes with known infestations; only 17 cases reported in states without endemic populations (Massachusetts, Maine, and California)

Likely risk factors

  • Invasion into spider habitat (e.g., handling old boxes, entering closets, basements)
  • Bites more likely in summer and at night


  • Serious reactions uncommon, but angio­edema, hemolysis, disseminated intravascular coagulation, and kidney failure reported
  • Based on review of 1,000 presumed/proven brown recluse spider bites over 35 years in the state of Missouri (estimated data, given lack of definitive diagnostic test)

—Necrotic skin ulceration in about 20% of cases (only North American spider bite frequently associated with necrotic skin lesions)

—No deaths

  • Pyoderma gangrenosum as a result of bite has been reported.

Chief concern

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  • Sensation at site of bite may range from pruritus to severe, burning pain.
  • Systemic manifestations may include fever, chills, nausea and vomiting, diarrhea, myalgias, arthralgias, malaise, rash, and headache.

History of present illness

  • Symptoms (if noted) typically develop two to six hours after bite.
  • Itching and burning may persist for up to one week and result in scaling and peeling.
  • Systemic manifestations (if present) occur within 24-72 hours.
  • Bite often is not witnessed, but individual may report recent activity in area of brown recluse spider habitat.
  • Systemic involvement more likely in pediatric patients


  • Most bites result in mild localized swelling and erythema; skin necrosis in up to 50% of patients in South America.
  • Hemorrhagic vesicles may develop with blanching of the skin around the perimeter.
  • Initial area of hemorrhage may degrade into area of central, blue necrosis by Day 3 or 4, followed by sloughing and sinking below the skin surface (“red, white, and blue” sign).

Making the diagnosis

  • No specific diagnostic test is available, and the condition may be overdiagnosed (used as a catch-all diagnosis for necrotic skin lesions of uncertain etiology).
  • No animal specimen is available for identification in 90% of suspected cases, but clinicians are still advised to be skeptical of undocumented patient claims of spider bites.
  • Multiple lesions are more likely to be of insect, tick, or mite origin or from some underlying dermatologic condition.
  • Identification of Loxosceles spider if captured is based on:

—Eye pattern (six, arranged in pairs/dyads, Loxosceles means “six eyes”; most other spiders have eight eyes arranged in four pairs)
—“Fat” body, 2-3 cm long, large leg-to-body ratio, characteristic pigmented violin-shaped pattern on the thorax.
—Commonly misidentified; expert identification preferred

Rule out

  • Bites/stings from other arthropods/arachnids (at least 60 species of spiders have been implicated in human bites)
  • Vascular occlusive disease, venous stasis, diabetic skin ulcers, vasculitis
  • Neoplastic skin disease, erythema nodosum, erythema multiforme, drug reactions
  • Infections (staphylococci and/or streptococci, cutaneous anthrax, erythema migrans [Lyme disease], fungal infections, leishmaniasis, atypical mycobacterial infection [e.g., scrofula], herpes simplex/zoster, syphilis, gonococcemia, necrotizing fasciitis)
  • Chemical burn, frostbite, etc.

Testing to consider

  • Complete blood count
  • Basic metabolic and coagulation profiles
  • Hemolytic profile (hemoglobin, lactate dehydrogenase, haptoglobin, urinalysis)


  • Typically self-limited without long-term sequelae (resolution of lesion within two to three days signals good prognosis)
  • Fatty areas, such as proximal thigh and buttocks, may develop more cutaneous reaction/extensive necrosis.


  • Clinical trial and observational data limited, but no intervention proven superior to conservative management (application of ice, wound irrigation, and tetanus prophylaxis)
  • Institute routine first aid measures as indicated (antivenin is not available in the United States but is available in South America), and consider hospitalization if evidence of systemic reaction or concerning/rapidly expanding skin lesion.
  • Routine surgical intervention at site of bite associated with increased incidence of complications without apparent clinical benefit.
  • No evidence to support use of hyperbaric oxygen, but application of electric shock to the skin lesion has been reported (case reports only) to provide symptom relief and promote tissue healing.


  • Carefully shake out clothes, shoes, and bed linens that have been stored in closets for long periods of time.
  • Wear long sleeves and gloves when entering potential habitat of brown recluse spider.
  • Move firewood and building material away from house foundation.
  • Reduce availability of insects serving as food source for spider.
  • Consider pesticide application.

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