Causes of Necrotic Wounds other than Brown Recluse Spider Bites

by Rick Vetter

updated October 2004

Throughout the United States, spiders get blamed as the cause of many dermatological wounds in medical diagnoses. In virtually every case, NO spider is seen nor felt inflicting a bite, nor is the alleged spider collected in the incident. "Potential spider bite" diagnoses are made solely on the symptoms of the lesion. In the case of necrotic wounds, "brown recluse spider bite" is a very common conclusion of medical personnel throughout North America including such ludicrously inhospitable places as Canada and Alaska where no brown recluses have ever been found. This is in spite of the fact that the brown recluse spider (Loxosceles reclusa) is native only to the South and central midwestern states (circumscribed by southeastern Nebraska south to Texas, east to Georgia/westernmost tip of South Carolina and southernmost Ohio with additional rare finds being made beyond this area). In addition there are several related species that exist in the southwestern U.S. deserts from Texas to California; however, they do not inhabit the coastal California regions where most of the human population is concentrated. (see distribution map) The members of the genus Loxosceles are known as recluse, violin or fiddleback spiders. Occasional, RARE occurrences of the brown recluse do occur outside this region because of the spider's proclivity to hide in boxes and the subsequent movement of possessions or commerce from its native area. However, occurrences outside the native areas are still extremely rare and they typically encompass finds of single specimens only, not burgeoning populations of these spiders. When people hear that there are no recluse spiders in their area, many immediately switch to hobo spiders or yellow sac spiders as their "recluse du jour", but the solid evidence of those spiders being involved is also lacking. People just WANT to blame spiders when there are lots of more probable things that cause necrotic injuries (see below).

When one finds a habitat that is conducive to recluse spider survival, no matter what the species, one does not find single specimens; one finds dozens of them. For example, a family of 4 in Lenexa, Kansas collected 2,055 brown recluse spiders in their house in 6 months. About 450 of these were large enough to cause envenomations, they saw brown recluses crawling all over the house, the walls, the carpet, in the sinks and bathtub, yet in 8 years of occupancy of that house (as of Sept 2004), no person or their multitude of pets has ever shown evidence of a bite (Vetter and Barger, Journal of Medical Entomology, volume 39, pages 948-951, 2002). Other people from endemic recluses areas like Arkansas, Alabama, Oklahoma, Missouri, Texas have written to me with similar stories. In comparison, transported spiders virtually never establish populations after being moved, the numbers of spiders found outside the native area of the brown recluse are very few yet diagnoses of their bites are hundreds and thousand times more plentiful than are verified finds of the spiders. It shouldn't take a math whiz to realize that the medical community is overdiagnosing brown recluse spider bites. If you truly think you were bitten by a recluse in your home, you should be able to find several specimens in a few days if you look for them. They are NOT hard to find where they prosper.

Please also be aware that far too many people continue to misidentify harmless spiders as brown recluses because they can imagine a violin on the spider. It is not that simple. Many spiders have dark markings on their bodies that look like violins to the non-arachnological public (cellar spiders, Oecobius, Mimetus, etc.) and have been misidentified because of that. Several of these spiders (i.e., Kukulcania, Anachemmis, Titiotus, etc.) do indeed look very similar to recluses so you have to be very careful in assuming that you have identified a spider correctly. It is always best to seek out a qualified arachnologist, who are unfortunately few and far between. Even entomologists, doctors and public health officials who lack training in arachnology have been overconfident of their abilities and have misidentified harmless spiders as recluses. I have even seen specimens from a Texas medical school that were not recluses but were being used to teach medical students what brown recluses look like. Therefore, the med students were getting incorrect information right from the start. I have been identifying spiders that people THINK are or might be brown recluses and have received nearly 1,700 spiders as of October 2004 and they have represented 36 different spider families; basically every genus of medium-sized brown spider found in America has been sent to me as a potential brown recluse.

In regard to diagnoses of "spider bites", the medical community is overreliant on the brown recluse as the causative agent of these wounds in many portions of the United States. In South Carolina, 940 physicians responding to a survey reported 478 brown recluse spider bites in their state in 1990; in stark contrast, the definitive scientific study on the distribution of all recluse spiders in the U.S. lists only 1 brown recluse from South Carolina. Recently, I have heard of several verifications of brown recluses in the westernmost tip of South Carolina around Greenville but they are virtually non-existent in the remainder of the state. In a 6-year database for the 3 Florida poison control centers, 124 brown recluse spider bites from 31 counties were diagnosed by medical personnel in that state (this is only a small portion of the actual number of diagnoses made). In comparison, in 100 years of arachnological information totaling over 100,000 identified spiders, only 11 finds of recluse spiders have been found in 10 counties and only 2 of these finds were in homes. In a study published in October 2003, four western U.S. arachnologists were contacted in regard to 216 brown recluse spider bite diagnoses made in California, Oregon, Washington and Colorado in 41 months. In contrast, only 35 brown recluse or Mediterranean recluse spiders could be verified as EVER being found in these 4 states. None of these 35 spiders was involved in an envenomation and in the 67 years of our collective experience, not one "recluse bite" victim has ever submitted a brown recluse to us for identification. In contrast, homeowners from endemic recluse areas submit brown recluses for identification about 70% of the time and people with necrotic skin lesions submit a recluse spider about 10% of the time. What should be becoming apparent to you is that 1) recluses spiders are common where they are found, 2) you need decent populations of them before you get a significant probability of a bite from one and 3) doctors from non-endemic areas are diagnosing bites from these spiders far out of proportion to the actual number of spiders that can be historically found in their states.

Medical personnel will diagnoses "brown recluse bite" because that is the most common and, unfortunately, most dynamic cause of necrotic wound that they have read about. Below is a list of skin afflictions that have been misdiagnosed as "brown recluse bite" by medical personnel. This list is published in the following Toxicon article and can be referenced as such. The second publication is a similar paper which details the overdiagnosis aspect in Florida. If you wish a copy of either or both of these articles, contact me and I will send one to you electronically in PDF form or as a paper copy.

  • Vetter, R. S., P. E. Cushing, R. L. Crawford and L. A. Royce. 2003. Diagnoses of brown recluse spider bites (loxoscelism) greatly outnumber actual verifications of the spider in four western American states. Toxicon 42:413-418.
  • Vetter, R. S., G. B. Edwards and L. F. James. 2004. Reports of envenomation by brown recluse spiders (Araneae: Sicariidae) outnumber verifications of Loxosceles spider in Florida. Journal of Medical Entomology 41: 593-597.

Conditions that have been misdiagnosed as brown recluse spider bites as reported in the medical literature

Bacterial Reaction to drugs
  • Staphylococcus infection
  • Streptococcus infection
  • gonococcal arthritis dermatitis
  • cutaneous anthrax
  • warfarin poisoning
Viral Arthropod-induced
  • infected herpes simplex
  • chronic herpes simplex
  • varicella zoster (shingles)
  • Lyme disease
  • Rocky Mountain spotted fever
  • Ornithodoros coriaceus bite (soft tick)
  • insect bites (flea, mite, biting fly)
Fungal Topical
  • sporotrichosis
  • keratin cell mediated response to fungus
  • poison ivy/poison oak
  • chemical burn
Lymphoproliferative disorders Underlying disease states
  • lymphoma
  • lymphomatoid papulosis
  • diabetic ulcer
Vascular disorders Misc./Multiple causative agents
  • focal vasculitis
  • purpura fulminans
  • thromboembolic phenomena
  • polyarteritis nodosa
  • pyoderma gangrenosum
  • pressure ulcers
  • Stevens-Johnson syndrome
  • erythema multiforme
  • erythema nodosum
  • toxic epidermal necrolysis
  • (Lyell's syndrome)

One of the more pertinent causes listed here is that the expression of Lyme disease can give the classic bulls-eye patterning characteristic of brown recluse bite. Misdiagnosis in this case can be rather disconcerting because Lyme disease can be treated and cured with common antibiotics. If diagnosed as brown recluse bite instead, it will obviously be treated as such and then the Lyme disease can progress into more serious symptoms of heart and central nervous system disorders. I have already helped one person in Rhode Island get away from his doctor's misdiagnosis of brown recluse bite (the closest native populations of recluse Rhode Island is southernmost Ohio) and on Lyme disease, which is what it was. In treating alleged spider bite victims, a question that medical personnel should also be asking is whether the patient has recently traveled outside the area where they live in case the patient might have been exposed ticks. Another consideration is being aware of potentially embarrassing etiologic agents such as filthy lifestyle habits (squalid conditions that might encourage vermin such as bed bugs).

If you have been diagnosed as having a brown recluse bite and you do not live within the native range of any recluse spider (see the map ) then there is minimal chance that your wound was caused by a recluse spider.

Finally, many people have contacted me and explained in detail the progression of their wounds.  Considering that the medical profession continues to misdiagnose skin conditions all the time and they see the wounds in person, there is little chance that I am going to be able to provide much more information from your written description over the internet other than the information I offer below.

  1. If you do not live in areas that are known to have recluses, then there is little chance of having a recluse bite. People constantly try to justify recluse bites because they have traveled recently or receive shipments from recluse-endemic areas. Although this is a logical consideration, in reality it has a very little chance of being the actual cause otherwise, arachnologists would constantly be finding recluses outside the endemic area. It just doesn't happen that often to justify bite considerations. If you print out this website, try to educate your doctor and he/she refuses to listen to your concerns of alternative diagnoses, find another doctor who is more willing to be educated or who already knows there are no recluses in your area.
  2. If there are multiple wounds in one person at once, or multiple wounds over a period of time, or multiple victims in a house, it is probably not a recluse bite. Multiple wounds are more likely the work of insects (fleas, kissing bugs) or arachnids (mites, ticks) that are seeking you for a blood meal or it is some underlying dermatologic condition (Staphylococcus infection, pyoderma gangrenosum). Please don't ask me what insects it might be, I don't know much about them. It will be best to ask your local entomologists or public health officials what biting insects are in the area. They vary greatly by region.
  3. Prisons, jails, correctional facilities, sports camps, military barracks, hospitals, nursing homes, long-term health care facilities - I get contacted every year by many prisons and other correctional facilities where the inmates are complaining that they are being bitten by brown recluses.  Yet when pest control personnel go in, they never can find the spiders.  I have been contacted by prisons in San Francisco, Los Angeles, San Diego, Ohio, Texas, and Arkansas.  The "bite victims" number from a few dozen to low thousands and sometimes include prison guards.  Yet no spiders.  In most of the cases so far, it has been determined that the cause was a contagious bacterial infection.  When officials started treating the condition with the proper antibiotics (e.g. clindamycin) as well as instituting changes of  more frequent hand washing and showering, more changes of clothes and bed linens, the condition came under control.  In the Ohio prison where an inmate died, it was determined that the source of the bacterial spread was crude tattooing being done with contraband needles.  Hospitals and military facilities are also places ripe for bacterial infections which are blamed on spiders because, similar to prisons, people are present up to 24 hours a day in close quarters.  One of the bacterial infections getting more attention now is MRSA (methicillin-resistant Staphylococcus aureus).  See article by Dominguez in references.
  4. General practitioners often go to the "brown recluse bite" diagnosis as a causative agent when they have little proof that a spider is involved.  The best thing to do is go to a dermatologist when the wound is fresh so he/she can do a biopsy on the tissue while it is being attacked.  When things start to scar over and heal, it is more difficult to assess the proper condition.  Physicians indeed have a difficult job in identifying skin lesions and in general, they do an amazing job in healing people.  However, they are not helping matters by diagnosing brown recluse bites from areas of the country where brown recluses are exceedingly rare.  From a decade plus of experience, I have found that doctors from endemic areas are much more conservative in diagnosing recluse bites because they know how rare bites actually are and they see real recluse bites occasionally.  In comparison, doctors in non-endemic areas will diagnose several recluse bites in a month, more recluse bites than spiders have ever been found in their entire states.


  • Anderson PC. Letter to the editor. Toxicon 1982; 20:533.
  • Anderson PC. Loxoscelism threatening pregnancy: five cases. Am J Obstet Gynecol 1991; 165:1454-1456.
  • Bennett, R. G. and R. S. Vetter. An approach to spider bites: erroneous attribution of dermonecrotic lesions to brown recluse and hobo spider bites in Canada. Canadian Fam Physician 2004; 50: 1098-1101.
  • Dominguez. It's not spider bites, it's community-acquired methicillin-resistant Staphylococcus aureus. J. Amer. Board Family Practice 2004; 17:220-226.
  • Kunkel DB. The myth of the brown recluse spider. Emerg Med 1985; 17:124-128.
  • Osterhoudt KC, Zaoutis T, Zorc JJ. Lyme disease masquerading as brown recluse spider bite. Ann Emer Med 2002; 39: 558-561.
  • Rosenstein ED, Kramer N. Lyme disease misdiagnosed as a brown recluse spider bite. Ann Intern Med 1987; 107:782.
  • Russell FE, Gertsch WJ. Letter to the editor. Toxicon 1982; 21:337-339.
  • Russell FE. A confusion of spiders. Emerg Med 1986; 18:8-13.
  • Russell FE, Waldron WG. Letter to editor. Calif Med 1967; 106:248-249.
  • Vetter RS, Bush SP. Additional considerations regarding brown recluse spider bites and dapsone therapy. Amer J Emerg Med 2004 22:484-485.
  • Vetter. R. S. Myths about spider envenomations and necrotic skin lesions. Lancet 2004; 364:484-485.
  • Vetter, R. S., G. B. Edwards and L. F. James. 2004. Reports of envenomation by brown recluse spiders (Araneae: Sicariidae) outnumber verifications of Loxosceles spider in Florida. Journal of Medical Entomology 41: 593-597.
  • Vetter RS, Cushing PE, Crawford RL, Royce LA. Diagnoses of brown recluse spider bites (loxoscelism) greatly outnumber actual verifications of the spider in four western American states. Toxicon 2003; 42:413-418.
  • Vetter RS. Brown recluse spider bite diagnoses and lawsuits. Pediatric Emergency Care 2003; 19:291-292.
  • Vetter RS, Barger DK. An infestation of 2,055 brown recluse spiders (Araneae: Sicariidae) and no envenomations in a Kansas home: implications for bite diagnoses in non-endemic areas. J Med Entomol 2002; 39:948-951.
  • Vetter RS, Bush SP. Chemical burn misdiagnosed as brown recluse spider bite. Amer J Emerg Medicine 2002; 20: 68-69.
  • Vetter RS, Bush SP. The diagnosis of brown recluse spider bite is overused for dermonecrotic wounds of uncertain etiology. Ann Emerg Medicine 2002; 39: 544-546.
  • Vetter RS, Bush SP. Reports of presumptive brown recluse spider bites reinforce improbable diagnosis in regions of North America where the spider is not endemic. Clinical Infectious Diseases 2002; 35:442-445.
  • Vetter RS. Myth: idiopathic wounds are often due to brown recluse and other spider bites throughout the United States West J Med 2000; 173:357-358
  • Vetter RS. Envenomation by an agelenid spider, Agelenopsis aperta, previously considered harmless. Ann Emerg Med 1998; 32:739-741.

    *** common spider was misidentified as a brown recluse by doctor***


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