Tell-Tale Signs It's Not a Brown Recluse Spider

It takes an expert to identify one, but almost anyone can say it's not

To identify a brown recluse spider you need a very strong microscope and a spider expert. These guys are tough to identify even by the experts. And unless you actually have a specimen to analyze, there's no way to know what it was that bit you or that scurried across the kitchen floor.

It takes a close examination of the spider itself to rule out all the other potential species that look like a brown recluse but don't pack nearly the same punch.

Likewise, you can't tell a brown recluse bite by the wound. There's no blood test or culture that can show the presence of brown recluse venom in a suspected spider bite.

There's no classically reliable pattern of signs or symptoms to help pinpoint a brown recluse spider bite.

If anything, identifying a brown recluse is more about ruling out what it isn't rather than figuring out what it is. Using these steps can help you figure out when it's not a brown recluse.

1

Brown Recluse Territory

Brown recluse distribution map

Rick Vetter

First, start with where you found the spider. Brown recluse spiders live in a well-defined area in the South-Central part of the United States. Within their habitat, they're hard to find. They are called "recluse" for a reason: They don't like to play with others.

These spiders like dark, dingy places. They hide under things and prefer living where the sun don't shine.

Inside their habitat, brown recluse spiders cause serious infestations. Where there is one, there are most likely dozens or even hundreds. However, even in homes with such outrageous infestations, bites are very rare.

The scientific name for the brown recluse is loxosceles reclusa. In all those other colored areas of the map are other loxosceles species (Texan recluse, desert recluse, etc). They're related to the brown recluse and all have similar venom. Indeed, some of the other loxesceles species have worse venom than the brown recluse.

If the spider was found outside of the known habitat of a brown recluse, then it is almost certainly not a brown recluse. Outside the other areas means it's not even related to the brown recluse.

If you have a specimen from inside the brown recluse zone (or if you think the experts are wrong about your particular spider even though you aren't in brown recluse territory) then let's try to figure out if it's not a brown recluse from its anatomy.

2

Legs: Slanted, Spineless, One Color

Loxosceles recluse spider capture in a plastic cup
Joao Paulo Burini / Getty Images

Loxosceles rhymes with isosceles, which you may remember from geometry is a type of triangle. The words are similar for a reason.

Loxosceles actually means slanted legs. If you look at a brown recluse from the side you can see how the body sits low and the legs angle up to a point. It's that angular, slanted shape of its legs that give the brown recluse its scientific name.

Two more distinct features of brown recluse legs:

  • No spines: Unlike many other spider species, loxosceles does not have spikes or spines on its legs. They are smooth.
  • One color: Some spiders have multi-colored legs, but loxosceles keeps it solid—no stripes and no patterns.

If your spider doesn't have these legs then it's definitely not a brown recluse. If you find these leg characteristics similar to your spider then look into its eyes, all six of them.

3

The Eyes of the Brown Recluse

Loxosceles
Pablo Dolsan / Getty Images

Assuming you're in brown recluse country and you have a spider with a low-slung body on angled, smooth, solid color legs, the next thing is to look your spider in the eye.

Brown recluse spiders have six eyes. They're paired in what are known as diads and arranged on the front and sides of the brown recluse's head. Other spider species might have eight eyes or they might have six eyes arranged in two triads (groups of three).

These guys are tiny, so seeing their eyes without a microscope is going to be difficult. If you have trouble reading fine print, you'll probably at least want a magnifying glass.

You can't be sure if it is a brown recluse based only on the eyes, but if the eyes aren't in the proper pattern then it's definitely not a brown recluse.

You got here because your spider had smooth, angled legs of all one color and you found it in brown recluse territory. Does your spider also have the proper peepers? If not, you're done here. If it does, move on to the rest of the body.

4

The Rest of the Body

Brown recluse (Loxosceles) spider on a ruler
Joao Paulo Burini / Getty Images

There are two more characteristics you need to see for this to be a loxosceles:

  • The body (without legs) has to be small, no more than 3/8 of an inch.
  • The abdomen (big round part on the backside) needs to be a little fuzzy with very fine hairs and a solid color.

Brown recluses are boring when it comes to fashion. They like solids. They aren't into patterns or stripes and that is obvious on their legs and abdomens. There is one common brown recluse fashion statement that everyone seems to know about: the fiddles on their backs.

5

Fiddleback Marking

Desert recluse spider close up
The classic violin mark isn't obvious on all species of loxosceles like this desert recluse, but the venom is just as bad.

Marshal Hedin

The one feature most commonly talked about in brown recluse descriptions is the violin-shaped mark on its back. Not all loxosceles are brown recluses, but they all have similar venom. Not all brown recluses have the classic violin mark. Even if it's there, you might not be able to clearly see it.

Worse yet, there are a bunch of spiders that also have the violin marking on their backs and they're not brown recluses. In many cases, they're not even venomous to humans. The worst-case scenario is that a doctor thinks you've been bitten by a brown recluse when you have not.

Counting on the fiddle to identify a brown recluse is a bad idea.

There's no antivenin—no specific treatment—for brown recluse bites, but many wounds that are diagnosed as brown recluse bites are actually infections and could be treated with antibiotics as long as your doctor diagnosis it correctly.

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Article Sources
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  1. Illinois Department of Public Health. Brown recluse and black widow spiders.

  2. University of Kentucky. Entomology. Brown recluse spider.

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