Tracking land policy in the Golden State.

The Persistent Myth of the California Brown Recluse

The dreaded Brown Recluse. Hide the children! | Creative Commons photo by A. Jaszlics

As the Southern California interior cools with aching slowness and temperatures threaten to drop into the 90s, desert dwellers start to come out of their long summer slumber and get some work done. For homeowners, gardeners, and anyone else charged with tidying up the brown and wizened late summer landscape, that can mean sticking their arms up to the elbow in dried weeds, wind-blown debris, and dead garden plants. And it's also about this time that those of us who work outdoors hear cautionary tales of the Brown Recluse spiders that lurk in that tall dead grass, and of the tale-teller's friend (or cousin or former co-worker) with a scar on his arm the diameter of a softball from an old brown recluse bite that invariably almost killed him.

It may ruin your enjoyment of those stories to learn that the Brown Recluse spider, Loxosceles reclusa, does not in fact live in California. What's more, even where they do live, they're shy, they can often be handled barehanded without incident, and the vast majority of the bites they eventually decide to inflict go almost unnoticed by their human victims. Almost all of the nasty sores blamed on Brown Recluses are caused by something else. We have nothing to worry about from Brown Recluses in California. At least that's what the debunkers say. But even though those debunkers are correct, the "Brown Recluse in California" situation is slightly more complicated than those baldly stated facts might lead you to believe.

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Here's the issue. There are no Brown Recluse spiders in California, at least hardly ever. Maybe six specimens of Loxosceles reclusa have been verified here in the state of California's history. Speaking purely statistically, it is more likely that you will have an affair with a sitting California Governor than that you'll see a Brown Recluse in the Golden State.

Recluses don't move around much. Many spiders can migrate by extending a strand of silk long enough to catch a breeze, then drifting on the wind for long distances. The arachnologists call this method of migration "ballooning," though it's really more like flying a kite than a balloon. Regardless of the terminology, it's an effective -- if somewhat aimless -- way for spider species to expand their range. And recluses can't do it. The only way Brown Recluses will ever get to California is accidental hitchhiking in some Midwesterner's moving boxes. (They seem to like cardboard.)

So: no Brown Recluses in California, practically speaking. You can exhale.

Ranges of Loxosceles species in the US | Map courtesy Rick Vetter, UC Riverside

Now inhale again. There are two other species of recluse spider resident in the state: Loxosceles deserta, the Desert Recluse, which lives pretty much where you might expect from the name and northward into the San Joaquin Valley, and Loxosceles laeta, the Chilean Recluse, an import that has gained a foothold -- presumably an easier task with eight feet -- in Los Angeles. Every once in a while a few individuals of the species Loxosceles rufescens, the Mediterranean Recluse, will show up on unloading cargo ships; no populations have ever been found in the state. The fun part: these other species of recluse spiders come in a whole rainbow of colors from pale buff to tan to manila to a deep, rich cafe con leche. Only Loxosceles reclusa is properly called the Brown Recluse spider. Those other species aren't Brown Recluse spiders. They're just recluse spiders that happen to be, well, brown.

Yeah, I find it confusing too.

Loxosceles deserta, the Desert Recluse | Creative Commons photo by Lynette Schimming

Really, what we have here, when this topic comes up, is yet another example of scientists and non-scientists using the same words, completely reasonably, to mean different things. It's the same phenomenon as we see in those depressing creationist arguments in which evolution, the best-established fact in the life sciences and the phenomenon without which, as biologist Theodosius Dobzhanski put it, nothing in biology would make sense, is described as "only a theory." To the biologist, "theory" is like a fact, only bigger: it's the conceptual framework on which you hang facts so that they suddenly all make better sense as a whole. To the layperson, "theory" means "wild and unsupported guess." Same word, two completely different meanings, both uses right in context, and confusion the result. Likewise with Brown Recluses versus recluses that aren't Brown Recluses in the strict sense but which are, nonetheless, brown. And recluses. The scientists say one thing, the non-scientists say the opposite thing, but they use the same exact words to say those two opposing things. It is of such complexities that a science writer's career consists.

More to the point, though: are the Desert Recluse and the Chilean Recluse as dangerous as the Brown Recluse? In the words of the Integrated Pest Management department at the University of California, Davis:

All Loxosceles spiders tested so far have the venom component that is capable of causing necrotic skin lesions, so it is best to assume that all recluse spiders may be capable of causing skin damage. In general, the desert recluse spider's venom is similar to that of the brown recluse and should be considered of equal potency. In comparison to the brown recluse spider, the Chilean recluse supposedly has venom more potent and the Mediterranean recluse's venom has been said to be less potent. However, these comparisons are more anecdotal than quantitive assessments.

The UC Davis IPM folks go on to say that:

About 10% of brown recluse bites cause moderate or greater tissue damage and scarring, but the vast majority heal very nicely without medical intervention. There is still not one proven death from brown recluse bite (a person was bitten by a spider caught in the act and properly identified). While there are several highly probable deaths reported in children, these are extremely rare occurrences, about one every decade or so.

You can also identify recluse spiders by counting their eyes. They have six, as shown on this Brown Recluse, instead of a typical spider's eight. Get out your hand lens!  Creative Commons photo by Jimmy Smith

People live around large concentrations of Brown Recluse Spiders in the Midwestern US and no one panics. Arachnologists handle members of a number of Loxosceles species somewhat casually, as you can see from the photos on this page of a bulletin board run by the Southern California Arachnid, Bug, Invertebrate, Entomological Society (SCABIES). A study published in 2002 cited a family in Kansas that collected 2,055 Brown Recluses from inside their house in a six-month period. At the time of the study, no one in that family of four had ever been bitten by a Brown Recluse. Five years later, according to one survey of the species, the mother of that household was bitten on the finger while doing laundry and the spider was positively identified. Her finger turned red and swelled slightly, and then she recovered.

So what's behind the panic? Unfamiliarity with the species is almost certainly part of the problem. Most Californians live within a few feet of a considerable number of highly venomous Black Widow spiders, and there isn't the same folkloric nervousness about that much more dangerous species. When a spider mostly lives in far-off places like Arkansas, it becomes more mysterious and its danger more alluring, a much better growth medium for urban legends.

And some of the nervousness seems to stem from the willingness of medical professionals to diagnose any necrotic skin lesion of undetermined cause as a "Brown Recluse Bite." According to that UC Davis site,

A world-renowned toxicology physician who worked at University of Southern California Medical Center estimates that most general spider bites in California referred to him were actually the work of other arthropods and that 60% of "brown recluse spider bite" diagnoses came from areas where no Loxosceles spiders were known to exist.

Other causes of necrotic lesions that are misdiagnosed as Brown Recluse bites include Lyme Disease, Herpes simplex, Herpes zoster (chickenpox or shingles), diabetic ulcers, and -- perhaps most troublingly -- group A Staphylococcus infections, which include methicillin-resistant Staphylococcus aureus (MRSA), popularly known as "flesh-eating bacteria." That last ailment can become quickly fatal if massive medical intervention is delayed for any reason -- including misdiagnosis as a spider bite.

All that said, there's still the off chance that you might find a Desert Recluse in the desert, and you might as well avoid an unpleasant interaction. They don't generally like non-native, irrigated plantings, but if you have a more naturalistic landscape setting, you might be providing them with the kind of habitat they like: under pieces of bark, in leaf litter, and detritus. They are reputed to be especially fond of desert woodrat dens. Move firewood and brush away from the foundation of your house, store your garden gloves and workboots in a sealed plastic garbage bag rather than out in the yard, and shake any such item of clothing out before putting it on, and you should be able to avoid becoming California's first completely authenticated Recluse Spider bite victim.

Not a Brown Recluse bite, though. Let's just get that part straight right here.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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Chris,
I never though I'd be able to read a whole article just about spiders. But I did, and enjoyed it, although I had to stop half way through after seeing that pictures of spider eyes (ahhhh!).. Thanks sharing all this info.

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Hey, thanks, Yoli!

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Thank you for the informative article. I do have to disagree that Californians do not have the same folkloric nervousness about black widows as brown recluses. As a parent of a small child I am equally concerned about all venomous critters that I am aware of. It also seems like a nit picky thing to say that desert recluses are not brown recluses. They are brown, they look incredibly similar, and have an equally venomous bite.
I do have a question for you. You mentioned that people have been bitten by the actual brown recluses and have had only minor swelling and that the only fatalities have been small children, is it true that one can get quite ill and have an wound that does require treatment from a doctor? Could that thought form be what causes people to panic about brown recluses. If it is, and they are not capable of such a feat could we just dispell that myth now and move on?