Don't Fear the Brown Recluse Spider (Seriously)

Brown recluse
The infamous brown recluse spider (Loxosceles reclusa) prefers to be left alone, will retreat if approached and will bite only if trapped, threatened or pressed up against the skin. Brown recluse spider bites are often the result of accidental contact. Wikimedia Commons

If you live in the United States, you've probably heard of brown recluse spiders (Loxosceles reclusa). While it's true the venom of brown recluse spider can cause nasty necrotic lesions in some and could potentially be deadly for a small portion of the population, it's pretty unlikely that any of the sensational stories you've heard about brown recluse spiders are true — even if they happened to your dad's cousin.

What Are Brown Recluse Spiders?

Recluse spiders belong to the genus Loxosceles, meaning "crooked legs," so named because their legs look like a bunch of old, bent-up metal coat hangers lying in a heap. They're a hunting spider, meaning they don't sit around in spider webs waiting for their supper to come to them.

Although they get around on strands of silk and make "silken retreats," or little shelters to hang out in, these dark brown spiders hunt their prey down on foot. Their ancestors were cave spiders, so in the wild, they like the dry areas beneath rocks, bark, shingles, woodpiles, etc.

But like rats, raccoons, flies and house sparrows, brown recluse spiders are synanthropic, meaning their numbers increase in association with humans.

Humans' homes are actually very much like caves, and a brown recluse loves nothing more than to lay her egg sac on the dry underside of the flap of a cardboard box and while away the hours guarding it in the eternal twilight of your attic.

Where Are Brown Recluse Spiders Most Common?

Just because brown recluse spiders like to hang out around humans doesn't mean they're absolutely everywhere.

"The distribution of brown recluses in the U.S. is a little like a rain cloud over the midwest," says Richard Vetter, a retired technician in the University of California Riverside urban entomology department. Vetter is also the author of "The Brown Recluse Spider" as well as articles in The New England Journal of Medicine and JAMA Dermatology. His work has changed the way doctors diagnose spider bites.

"If you're standing in the center of the storm — in Kansas or Oklahoma — you're going to get very wet," Vetter says, "a lot of water droplets are going to hit you. If you're standing at the edge of the thunder shower in Georgia, the droplets will be much fewer and farther between."

In one 2009 paper, Vetter and his coauthors discovered that at the southeastern edge of the spiders' range in the state of Georgia, hunters found only 25 brown recluse spiders over the course of a five-year search.

Compare that with the one Kansas residence in which the homeowner collected 2,055 brown recluses over the course of six months.

The Truth About Brown Recluse Spider Bites

Brown recluses do bite on occasion. The owner of the Kansas residence harboring a brown recluse spider infestation lived there for 11 years before knowingly sustaining a brown recluse spider bite, which ended up being asymptomatic.

"She reached inside a shirt, felt a pinch and the spider fell out," Vetter says. "She says she took a Benadryl and went on with her day. She was fine. I'm not sure the Benadryl did anything."

Not everyone who is bitten by a brown recluse spider experiences a reaction — not by a long shot. In fact, 90 percent of all brown recluse bites result in absolutely nothing. Just about 10 percent of cases result in a necrotic skin lesion (rotting flesh) that may require a skin graft, but even that lesion usually heals up completely by itself.

In much less than 1 percent of cases (usually in small children) the reaction to brown recluse venom becomes systemic, destroying red blood cells and causing toxic backup in the kidneys. In these cases, hemoglobin passes into the urine, which comes out black. If this happens, the patient could die within 12 to 30 hours — even before anything shows up on the skin around the bite site.

So, if you notice your or your child's urine is black, seek medical attention immediately. According to Vetter, dialysis and hydration should clear it up if you catch it in time.

Can You Die From a Brown Recluse Bite?

A brown recluse bite is rarely fatal. While the venom causes an injury that may take several weeks to heal, you are not likely to die from it.

"Even though fatal brown recluse bites are unbelievably rare, that's what makes the news," Vetter says. "Say you know nothing about car accidents and all you know about them is what you've seen on the news. The only car accidents anybody reports on are the ones that involve fatalities, so if you don't know better, it's easy to believe that all car accidents kill people. The truth is, most of the time somebody just gets a fender bent in a parking lot and drives away."

Misdiagnosis Is Common

People sometimes blame brown recluse spiders for crimes they didn't commit, with the issue revolving around a misdiagnosis. According to Vetter, many physician-diagnosed spider bites are actually not spider bites at all.

"Bacterial infections, fungal infections, all kinds of viruses are misdiagnosed as brown recluse bites," Vetter says. "Once I was called by a military base in the northeast because all the soldiers were coming down with these inflamed skin lesions. They were trying to get a permit to spray for spiders. The description of the lesions didn't sound like necrotic brown recluse bites at all — they were swollen and red, and necrotic recluse bites become sunken and blue."

Vetter continues, "I told them as much, and a few months later they called back to tell me it was actually MRSA, a bacterial infection, going around the base. But, you know — people are very prejudiced against spiders."

Spiders Are Difficult to Identify

According to Vetter, brown recluse spiders end up taking a lot of heat partly due to the fact that most people don't know the first thing about identifying spiders.

"I did a study where I got people to send me brown recluses they found from all over the country. If you thought it was a brown recluse, you stuck it in an envelope and sent it to me," Vetter says. "Over four and a half years, I was sent 1,800 specimens representing 158 species — some were pseudoscorpions, I got some granddaddy longlegs, a little of everything. Basically, if it has eight legs, people think it's a brown recluse."

Now That's Interesting

About 40 different medical conditions are commonly misdiagnosed as brown recluse bites, from vascular disease to leukemia. Many of these are much worse than a brown recluse spider envenomation could ever be.

Original article: Don't Fear the Brown Recluse Spider (Seriously)

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