Rick Vetter
Department of Entomology, University of California, Riverside, CA

This website presents evidence for the lack of brown recluse spiders as part of the Californian spider fauna. Unfortunately, this contradicts what most Californians believe; beliefs that are born out of media-driven hyperbole and erroneous, anxiety-filled public hearsay which is further compounded by medical misdiagnoses. Although people are free to disagree, this opinion has come about after more than two decades of constant research resulting in many publications in the scientific and medical literature. In addition to personal experience and thousands of spiders submitted to UC Rverside, the sources for this opinion encompasses conversations with, interactions with, and the cumulative knowledge of the following, who have experience or expertise in the state of California and, in some cases, are national or international experts:

  • Arachnologists throughout the state including those at the Los Angeles County Museum and San Francisco's California Academy of Sciences (one of whom is probably one of the top 5 arachnologists in the world)
  • The Calif. Dept of Food and Agriculture, which is responsible for identifying all exotic pests found in California
  • County Agricultural Commissioner Office entomologists up and down the state
  • Hundreds of pest control operators in both Northern and Southern California
  • County vector and health personnel
  • A U.S. recluse expert, who wrote the definitive taxonomic revision where he described the distribution of all North American recluse species, and who also happened to be a vector control person in Northern California, now retired.
  • The late Dr. Findlay Russell, the world's foremost authority on animal venoms. Dr. Russell was an internationally renowned toxicologist, was a medical physician at USC Medical Center and consulted on hundreds of "spider bite" diagnoses in California. In fact, Dr. Russell's research was the impetus for many of the ideas expressed here.

Cumulatively, this body of knowledge represents hundreds of years of experience with spiders and/or their medical aspects in California and the identification of hundreds of thousands of spiders. So if you think the material here is in error, consider the strength of your own sources.

Spiders are one group of arthropods that are very well known by the common person yet are terribly misunderstood; because of the rare occasion of a deleterious venom incident, almost all spiders are lumped into the category of "squish first and ask questions later". There are remarkably few spiders in California that are capable of causing injuries via biting. Overall, spiders are beneficial to humans in that they eat many pestiferous insects that either infest our foods (many phytophagous insects), are vectors of disease(flies, mosquitoes) or are aesthetically-challenged (cockroaches, earwigs). Unfortunately, humans have a low tolerance for spiders in their homes, either because spiders are symbols of danger, unkemptness or arachnophobia. One of the first steps one should take in dealing with these critters should be to identify them properly before blasting them with pesticide and/or getting hysterical.

There are no sure long-lasting control measures for spiders, however, mostly what pest control operators are dealing with in this situation is a psychological problem rather than an entomological one. Folks want spiders out of their homes because of fear and/or repulsion. The assumed risk of spiders in one's home is much greater than the actual risk they pose and home owners probably do more harm to themselves by using large amounts of pesticides inside a home to kill spiders than any harm the spiders could actually do to them. Unfortunately, the quantities and habits of spiders cause them to reinfest areas soon after treatment so it is difficult to eliminate spiders altogether.

The spider that poses the greatest health threat to humans in California is the black widow spider, Latrodectus hesperus. Before antivenom was available, bites from these spiders caused death in about 5% of the cases. Currently there are adequate medical treatments; deaths from black widow bites are virtually non-existent. This adult female spider is readily identifiable because of its unique coloration: a shiny black body with red hourglass on its belly (not on its back as lots of people think). However, the western black widow looks very different as an immature because it starts out life bedecked in tan and white stripes. As spiderlings mature, more black pigmentation is deposited in the integument with each molt until they turn completely black. Males retain the coloration of the juvenile striped pattern and are often turned into our department because folks are afraid that they are brown recluses.

The next "spider" most familiar to Californians-the brown recluse-is a myth. There are no populations of brown recluse spiders living in California. In case, this upsets your applecart, I repeat, there are no populations of brown recluse spidersliving in California. The common name "brown recluse spider" refers to one species of spider, Loxosceles reclusa, which lives in the central Midwest: Nebraska south to Texas and eastward to southernmost Ohio and north-central Georgia (see map). Only a handful of specimens (less than 10) have ever beencollected in California and usually there is some connection between the spider and a recent move or shipment from the Midwest. There is a great "awareness" of brown recluse spiders in California mostly through a misguided media barrage which is fed by a fear of the unknown and unfamiliar. I repeatedly have seen the media in their "quest to seek out the truth" write completely speculative stories about the existence of the brown recluse in California. Unfortunately, the truth is not nearly good enough to sell news and therefore, a speculative story is fabricated based upon faulty assumptions. Rampant recluse phobia is based on people's willingness to believe the worst about a situation and the sensationalistic news media who scream about the POSSIBILITY of one spider being found in California. Actual titles from newspapers regarding recluse stories are "Necrotic Wound Blamed on Elusive Spider" , "Spider-bite Terror in Calif.", "Likely Bite by Spider Changes Life". Notice how carefully the titles are chosen. They don't say that they have found the spiders or that a population of the spider has been verified. They report the belief that the spiders are here or have caused damage. Many times the speculative stories are based on the premise that a brown recluse COULD be found in California. While this is certainly true (since people move from the Midwest each day), it is also true that because I am a male, I could have an illicit and immoral relationship with a Playboy bunny. This is definitely a possibility. However the chasm between "POSSIBILITY" and "PROBABILITY" is so wide you couldn't build a bridge between here and there. A more tenable example is that someone COULD win the California state lottery grand prize by buying one ticket a year. This is definitely a possibility. However, the probabilityof this is obviously so close to zero that it is effectively zero. As they say, the lottery is a tax on those bad in math. Still there are many more California lottery grand prize winners than brown recluse spiders found in the state each year. Although there is the chance a brown recluse could be in California, that one little spider is not responsible for the several hundred brown recluse spider bite diagnoses that have been made in California and the probability of being bit by a brown recluse in California is realistically zero.

In its native range, the brown recluse is a very common house spider. A colleague in Missouri found 5 in a child's bedroom one night, a person in Arkansas found 6 living under his box spring in his bedroom, during a cleanup at the Univ. of Arkansas, 52 were found in a science lab that was being used everyday, a colleague found 9 living under one piece of plywood in Oklahoma, a grad student and I collected 40 of them in a Missouri barn in 75 minutes, and would have collected more, but we ran out of vials to house them. One amazing story is an 8th grade teacher in Oklahoma checking up on his students avidly collecting material by some loose bricks around a flagpole on an insect collecting trip. In about 7 minutes, 8 students collected 60 brown recluses, picking them all up with their fingers and not one kid suffered a bite. An even more amazing story is that of a woman in Lenexa, Kansas who collected 2,055 brown recluse spiders in 6 months in 1850s-built home.  This family of 4 has been living there 8 years now and still not one evident bite.  (see Vetter and Barger 2002, Journal of Medical Entomology 39: 948-951). When you find brown recluses in an adequate environment, you do not find one, you find dozens. And yet, the people who live with these spiders rarely get bitten nor do they run around in constant fear. With the current paranoia, if we had populations like that in California, they would evacuate the state and close it down. The California reaction to the mythical brown recluse is based solely on the fear of the unknown and the willingness to believe that there is an 8-legged menace running around causing havoc. I was interviewed by a local newspaper reporter looking for a sensationalistic sound bite. The question was, "What do you think the effect of this brown recluse event will have on southern California?" My answer was "All the tourists from Missouri, Arkansas and Kansas are laughing themselves off their hotel beds because a story on one alleged brown recluse spider found in Los Angeles makes the evening news."

Yet the finding of one alleged brown recluse in California is enough to get the news hounds barking for a story. A California county entomologist said that when he found a potential recluse spider, he had 2 television news trucks parked outside his office waiting for him because they wanted to get "THE STORY". In 1998 or so, there was a rumor that a Marin County park ranger and 2 others were dead from brown recluse bites. People freaked out. One woman called a taxi cab, handed the driver some money and a dead spider and told him to deliver it to the County Agricultural Commissioner's Office for identification. (Apparently the driver just took the money and drove off, never delivering the spider.) No park ranger died and it was just hysteria. Other news articles abound when there is the "thought" that a brown recluse might have been found in California. How ludicrous do you think this looks to the rest of country? How hard is that Arkansas guy laughing who was sleeping on top of 6 brown recluses? How much head-shaking does the woman in Nashville do who collected 7 running through her apartment in one month? How about the Kansas arachnologist who found 12 under a rug in a doghouse? (Actually, he does laugh pretty hard every time I relate a California brown recluse paranoia story to him.) How about the Oklahoma kids who each collected an average of 1.07 brown recluses per minute where it would take the average kid in that group 8 minutes to collect more brown recluses than has the entire California populace (currently about 32 million people) in 40 years? People get all worked up and say, "BUT IF THEY FOUND ONE BROWN RECLUSE IN CALIFORNIA THAT MEANS .." It means they found one, it is smashed, mangled, mutilated, pickled in alcohol, dead, deceased, passed on, no more, ceased to be, bleeding demised, bereft of life, resting in peace, gone to meet its maker, pushing up the daisies, rung down the curtain and joined the choir invisible, etc. and no longer poses a threat to humanity (not that it posed a great threat to begin with). THIS is an ex-spider! Brown recluses are almost communal and can be found in great numbers. If you truly have a brown recluse infestation in your house or your community, then you should readily be able to find dozens more with little effort. Once again, every few years a brown recluse can be found in the state but it is a single itinerant that was brought here, is not the tip of a massive invasion and does not justify hundreds of medical misdiagnoses, hyperbolic news stories nor public hysteria. If they truly lived here then you should be able to find many specimens for identification.

The myth of the brown recluse reinforces the misconception to the medical community that the brown recluse lives here whereupon they make misdiagnoses. In "alleged brown recluse spider bites" in California, almost never is any species of spider collected nor identified in the incident and if it is, never has it been a verified brown recluse. There are many different causative agents of necrotic wounds, for example: mites, bedbugs, a secondary Staphylococcusor Streptococcus bacterial infection. Three different tick-inflicted maladies have been misdiagnosed as brown recluse bite: Lyme disease, Rocky Mountain Spotted Fever and the bite of the soft tick, Ornithodoros coriaceus. How would you feel if a Californian physician treated you for the bite of the non-existent brown recluse and instead you developed advanced stages of Lyme disease (heart arrhythmias, central nervous system disorders) which is easily curable in the early stages with common antibiotics? Additional non-arthropod generated agents have also been labeled as brown recluse bites including: poison oak/ivy, infected and chronic herpes simplex, diabetic ulcer, pyoderma gangrenosum , lymphomatoid papulosis (skin cancer), sporotrichosis (fungal infection), shingles, adverse reaction to prescribed drugs, etc. The necrotic lesion causative agent that comes to physicians' minds most easily is "brown recluse bite" and unfortunately, that is the one they use for a diagnosis, being totally unaware of the local distribution of the spider. Every month in California, more people are diagnosed as having brown recluse bites than the total number of brown recluse spiders EVER collected in the state. It has been estimated that in one study, 60% of all "alleged brown recluse spider bites" occurred in areas where no Loxoscelesspiders have ever been found. Every once in a blue moon a brown recluse is found in the state and it is not impossible for someone to get bitten by one. However, a rare event (importation of a brown recluse) followed by a very rare event (the probability of any individual actually being bitten by the one brown recluse that makes it into California) yields a total probability very near zero. In contrast, I have personally heard of several hundred brown recluse spider bite diagnoses made in California in the last decade. This is a mere fraction of the thousands that undoubtably have been made by the medical community. Yet so far less than 15 verified specimens of the spider have been found in the state in the last 40 years. Do you really feel that the finding of one brown recluse spider every few years justifies these thousands of medical misdiagnoses? Does it make sense that even though a small fraction of 1% (and possibly none) of the brown recluse spider bite diagnoses in California are correct that this justifies doctors continuing to make these diagnoses?

In Tennessee where they have brown recluses, a bite victim brings a brown recluse spider to the doctor about 20% of the time. If the same percentages were true for California, patients would have already turned in hundreds of brown recluses to their doctors over the last decade and we would be able to easily find hundreds of recluses in the state. I have polled California county entomologists, vector control personnel and arachnologists regarding the number of spiders that have been submitted to them by the California public and how many were brown recluses. So far, over several decades, about 20,000 spiders have been turned in by concerned Californians and none have been brown recluses.  In comparison, I have received somewhat over 500 spiders from people from endemic brown recluse regions (Kansas, Missouri, Oklahoma, Tennessee, Nebraska) wanting to have their spiders identified, about 75%of these werebrown recluses and all were collected romping through their homes. These people are living with dozens of recluses in their homes, more than the statewide total everfound in California, and yet they don't receive bites and aren't walking around like they belong in a Wes Craven schlock-horror movie. Why can't Californians find recluses? Do the spiders become invisible once they reach California? Are the spiders much sneakier or more aggressive when they cross the state line? Are Californians much more pathetic in their ability to find recluses than people from Tennessee and Kansas? No! Is it possible that another spider is causing these "brown recluse wounds"? Maybe. While this is possible, with all the thousands of "brown recluse spider bite" diagnoses made in California and throughout the country, why haven't people been finding another spider once in the while in the act of biting? Some wounds possibly are spider bites but they are still grossly overestimated. There is no denying that necrotic wounds are occurring in California but as long as people keep alive the myth of the brown recluse, the real causes of these wounds will continue to be a mystery.

We do have other Loxoscelesspiders in California, the most common being Loxosceles deserta, found in the sparsely-populated eastern California desert regions in goodly numbers. There are no established populations of native Californian violin spiders in the urban non-desert California areas. The native violin spiders are not considered to be as dangerous as the brown recluse, but then again, many brown recluse bites are medically unremarkable. In southern California, we have a South American violin spider, Loxosceles laeta, which is supposedly more virulent than the brown recluse. It inhabits a small area of Sierra Madre, Alhambra, San Gabriel and Monterey Park but has not expanded greatly from this region. Despite this situation, these areas ARE NOT hotbeds of necrotic wounds and there has not been one verified bite incident involving L. laetain California because they mostly live in basements and steam tunnels and are not being turned in by the public so they are not found or, at most, are extremely rare in people's homes. Finally, in Chile where L. laetais native, a spider census turned up an average of 163 live violin spiders living in the 5 most infested homes (range 106 to 222 spiders). And no one living in those houses had ever shown evidence of a recluse bite.

At this point, one might say "Okay so we don't have brown recluses but we do have these other violin spiders. See!!!" Nope, yet another witch hunt. Just because we have violin spiders does not mean that they are causing all these wounds. In fact, most of the brown recluse spider bite diagnoses I have heard about have come from coastal and Northern California, in cities where no species of recluse has ever been known to live. One should not call something a spider bite unless a spider was removed from one's skin in the act of biting, seen biting flesh and then running off, found crushed in the remains of clothing near the bite site or if a person with necrotic wounds lives in a house that is infested with violin spiders. You need to have the "smoking gun". Otherwise, it is baseless speculation. If the spider was on trial, it would never get convicted with most of the "evidence" that people could produce. But many folks don't like the answer of "I don't know" for the cause of their necrotic wound and instead are very determined to pin it on the brown recluse. They want to blame something concrete and the brown recluse is the scapegoat for their desires. Yes, indeed, necrotic wounds are occurring but it probably is not a spider doing it.

One of the best ways to ascertain the rarity of all violin spiders in California is to identify those spiders which everyone thinks are "potential brown recluses". Most spiders have 8 eyes arranged in 2 rows of 4. Violin spiders are very easily identifiable in that they have 6 eyes, in 3 pairs (dyads) arranged in a U-shaped line on the cephalothorax (link here for pictures). There is a dyad in front and a dyad on each side. In brown recluses and the south American violin spider there is a distinct violin shape as well on the cephalothorax; in the native Californian Loxoscelesspecies, the violin pattern is rather indistinct and commonly non-existent. If a Californian spider does have 6 eyes, they are usually in a different configuration (e.g., 3 eyes together in 2 triads) or there is one pair of eyes that is very small and hard to discern. There are some native Californian spiders (Scytodesspp., Diguetiaspp.) which one can find in the eastern deserts with a similar eye pattern as Loxoscelesspiders, however, they have stripes and differing colorations on the dorsal body parts that readily signify that it is not a violin spider. Despite the fact that one can learn to discern a brown recluse from almost all spiders in 5 seconds, I have seen harmless 8-eyed spiders that were misidentified as brown recluses by 1) 3 different physicians, 2) an entomologist and 3) a pest control person. The lay community relies on folks like these as authorities, yet these people go around without the proper knowledge and are continuing the myth of the brown recluse.

Because people know of UC Riverside's Entomology Department, an amazing number of spiders come into the department in the ubiquitous baby food jars. During a stretch of several years during a brown recluse hype, about 200 spiders were brought to the department, about 75% because folks wanted to know if they were brown recluses. Of course, none of them were. Some of the most common ones brought in were the false black widow (Steatoda grossa), male black widows, wood louse spiders (Dysdera crocota), wolf spiders, daddy-long leg spiders (also known as cellar or pholcid spiders). Some of them haven't even been spiders (opilionids and solpugids) and the only aspect that seems to be consistent amongst all these submissions is brown color and 8 legs.

Finally, despite all my antagonism, I fully realize that someday someone somewhere may find a thriving population of brown recluse spiders living in California. But to date, this has not happened despite 1) the overwhelming public concern about the presence of this spider in the state, 2) the false belief that it already is here and causing massive damage and 3) the voluminous collections, spanning several decades and including hundreds of thousands of spiders, by many arachnologists, amateur and professionals alike. One reason for my verbal assault is that I want to get folks as incensed about finding a real brown recluse as I get incensed about all these folks telling me that brown recluses are everywhere. It is really amazing that wherever I go (the supermarket, dental appointments, on campus, etc.) any place where one makes idle chit-chat, folks are always telling me that they have found brown recluses, are afraid of brown recluses, have been bitten by brown recluses, have had neighbors die or lose limbs to brown recluses. The brown recluse has been elevated to a major urban legend status very much like UFOs, Bigfoot and Elvis. There is this mythical characteristic about their legend and the fear they invoke such that the majority of people I run into in California are either convinced that brown recluses live here or are surprised to find out that they don't. The biological evidence that is available resoundingly deflates any of the arachno-propaganda that is constantly being given new life with each newspaper story or word-of-mouth tale of terror. I emphatically state THERE ARE NO BROWN RECLUSE SPIDERS LIVING IN CALIFORNIA.

Original Posted on the UC Riverside Website