Brown recluse

The Brown recluse (Loxosceles reclusa) is a particularly notable spider, not only for its necrotizing venom, but for the strong and persistent myths surrounding its geographic range[1] and alleged evil tendencies.^{[citation NOT needed]}

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Range

Contrary to popular belief, the recluse is not an omnipresent, evil creature from the pits of hell, and is in fact from almost entirely the Midwest and South, with possible extremely small and confined populations existing in other states. However, a closely related species, the desert recluse (L. deserta), is present in southern California, Nevada, and Arizona,[2] which also possesses necrotizing venom, likely of similar potency.[3] Additionally, the Chilean recluse (Loxosceles laeta), which definitely has worse venom than the desert recluse, does exist in the US in small areas around California's border with Mexico, but is not known to bite. Though these spiders do exist in America, their marginally lesser danger and smaller US range make the brown recluse a much more effective target for media attention and the public version of Headless Chicken Mode.[1] There are several main things that cause brown recluses to be "found" where there aren't any.

Misidentification

Most people are not arachnologists, entomologists, or in any way interested in learning how to tell the difference between a brown recluse and an entirely different brown spider, so it's very easy to misidentify anything that even slightly resembles the brown recluse as one, possibly including dust balls.^{[citation NOT needed]} Spitting spiders, cellar spiders, house spiders in the Kukulcania genus, funnel weavers, orb weavers, huntsman spiders, even a solifuge,[4] which isn't a spider, and many more have all been mistaken for recluses[5][6] despite many of those clearly not being recluses when compared with a picture of a real one. This misidentification could be attributed to never actually seeing a recluse, in which case only the most common physical description (brown with a violin on its "back") would be used.[4] In reality, this violin marking must be present along with six eyes, a body length not exceeding about half an inch, and uniform coloration throughout the entire body to be able to say with some certainty that a spider is a brown recluse.[7] And, of course, you need to live somewhere that's not super far out of its range.

Misdiagnosis

While medical doctors are generally good at what they do, it is important to remember that they should not be considered experts on things outside of their field. Therefore, asking them to identify a spider bite is not a good idea, though you can ask them to treat the bite once you know what spider did it. If you have the spider that bit you, ask an arachnologist or entomologist rather than a doctor to identify it for you, and if you don't have the spider, it may not even be a spider bite.[8] Even when a bite does come from a brown recluse, it rarely, if ever, manifests as the type of thing you see in media. Wounds that are gigantic and awful are often due to infection on the bite site, or are due to infection and no bite at all. Some diseases that can be misdiagnosed as recluse bites are anthrax, Staphylococcus or Streptococcus infection, especially MRSA, Lyme disease, Pyoderma gangrenosum, herpes, syphilis, and vasculitis.[9]

Bite severity

Even if you do live in the brown recluse's natural range, it's unlikely that you will be bitten and even more unlikely that the bite will do serious damage. There is a reason their name is the "brown recluse"; they want nothing to do with humans and accordingly shun contact as much as possible. As an example, a home in Kansas was infested with slightly over 2,000 recluses, 400 of which were large enough to bite a human, yet nobody living there was ever bitten. Investigations of other less severe infestations yielded the same results.[10] The probability of necrosis is probably under 50%, and it is agreed that the percentage of necrotic wounds attributed to recluses is higher than the reality.[11][12] Systemic reactions are also rare, though the exact percentage of the time that they occur varies wildly by source.[13][11] The spider bites only in defense, when it is pushed into or trapped against skin, such as when you put on clothes that it was sitting in or stick your hand into a pile of wood.[14][15] So just be careful if you live in its range, and you should be fine.

References

1. Myth of the Brown Recluse
2. Distribution of Brown spiders native to the United States - Loxosceles
3. Loxosceles deserta spider venom induces the expression of vascular endothelial growth factor (VEGF) in keratinocytes
4. Why You Need Not Fear the Poor, Misunderstood Brown Recluse Spider (don't look at the images if you're squeamish)
5. How to Identify and Misidentify a Brown Recluse Spider
6. Identifying and Misidentifying the Brown Recluse Spider
7. Pests of Homes, Structures, People, and Pets
8. Spider Bites
9. Wikipedia article on the brown recluse
10. An Infestation of 2,055 Brown Recluse Spiders (Araneae: Sicariidae) and No Envenomations in a Kansas Home: Implications for Bite Diagnoses in Nonendemic Areas
11. Brown recluse spider bites to the head: three cases and a review.
12. Is It a Spider Bite? Probably Not
13. Brown recluse spider bite death of Alabama boy rarer than dying by lightning strike
14. Brown recluse spider behavior
15. Brown Recluse Spider — University of Kentucky