Tag Archives: brown recluse

How to tell if a spider is not a brown recluse

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UPDATE (Oct. 2017): We have just launched a new community science and public education initiative called Recluse or Not? This is a collaboration with Eleanor Spicer Rice and Matt Bertone that will allow us to obtain information about where people are finding recluse spiders inside and outside their native range in North America and help people to learn more about recluse spiders and how to identify them. Please check out the project page here for more details, and send us your photos of suspected recluse spiders on twitter! If you are not on twitter, please feel free to email me (you can find my contact information on the “about me” page).

This post addresses one of the most common spider identification questions in North America (north of Mexico): is it a brown recluse?*

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A female brown recluse, Loxosceles reclusa. Photo: Alex Wild, used with permission.

The brown recluse spider (Loxosceles reclusa) is arguably the most feared and most misunderstood spider species in North America. So, here we will find out how to tell if a spider is not a brown recluse. But before we do, it’s important to note that even if you do find a brown recluse, it’s not that big a deal.

Arachnologist Rick Vetter is an expert on the brown recluse spider who has done a ton of research on where they are (and aren’t) and how dangerous they really are (hint: not as dangerous as you think), as well as spending a lot of time dispelling myths and misconceptions held by both the public and the medical community. His website is full of excellent resources, and is the source of most of the information here. I encourage you to peruse his website and the articles linked in this post yourself, but I will highlight a few of the more compelling reasons that the brown recluse hysteria is unwarranted.

recluse_infestation_Abstract

Exhibit A: brown recluse bites are rare even where the spiders are abundant.

A family lived in a house full of brown recluses (more than 2000 of them!) for half a year and not a single bite occurred. Even in places where brown recluses are common, bites are very rare. Of those rare bites the vast majority of bites can be effectively treated with RICE (rest, ice, compression, and elevation) without any dire consequences. The small percentage of bites that are very serious are the ones that get all the attention in both the medical literature and the media, which has led to the misconception that recluse bites are always severe, require hospitalization, result in extensive scarring, and so on. Furthermore, misdiagnoses of all manner of other (more serious) conditions as brown recluse bites are rampant throughout North America (even in areas where the spiders do not occur), adding fuel to the already raging fire.

Now that all that’s out of the way, here is a series of questions to determine if a spider is NOT a brown recluse**. (Some of these may seem silly, but many of the spiders below that are not brown recluses are regularly misidentified as brown recluses by non-experts. Many people aren’t aware just how many different kinds of spiders there are, and for some, seeing brown, any marking vaguely reminiscent of a violin, and 8 legs is enough to conclude that a creature as a brown recluse.)

For those who want to skip the fine print, if the answer to question 1a or 1b is “yes”, it’s probably not a brown recluse. If the answer to any one of the remaining questions is “yes”, it’s definitely not a brown recluse. 

1a. Are you in Canada (or Alaska)?

brown_recluse_map_Canada_no_text

The range of the brown recluse spider does not extend into Canada. If you are in Canada, you are extremely unlikely to encounter a brown recluse spider. (Also see notes under 1b.)

1b. Are you in a state outside of the range of the brown recluse?

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Above is a map of the known ranges of all of the species in the genus Loxosceles in North America. If you are anywhere outside the red-outlined region, you are very unlikely to encounter a brown recluse.

[update 2021] Below is an updated range map based on the latest data, made by Matt Bertone. For more information about recluse spiders, check out our Recluse or Not? page.

Brown recluses are occasionally found outside this range – sometimes they hitch a ride with people moving around the country (in boxes that have been stored in basements, for example). But even in these cases they will typically remain in the building into which they are introduced because they are very poor dispersers. Just because one or a few brown recluse spiders have been found in a new area does not mean that their range has expanded or that they are abundant there. (Note: A brown recluse spider bite diagnosis in an area outside their range does NOT mean that brown recluse spiders have been found there. Many doctors erroneously diagnose spider bites in the absence of any evidence, namely a spider that has been identified as the culprit.)

2. Is it on a web out in the open?

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Some brown web-building spiders that are not brown recluses. Clockwise from top left:       common garden spider (Araneus diadematus) on orb-web, dome-web spider male (Neriene radiata) false widow spider (Steatoda grossa) on cobweb giant house spider (Eratigena atrica) on funnel-shaped sheet web. Photos: Sean McCann.

If you find a brown spider on a web out in the open, it is not a brown recluse. Unlike the various brown web-building spiders shown above, each with their different types of web, brown recluse spiders do not use silk for prey capture. They do build small irregular silk retreats in which they hide during the day. These retreats are made low to the ground and out of sight in cracks and crevices or under objects like rocks.

Update (8/06/2015): I should mention that house spiders in the family Agelenidae are probably the most likely spiders to be mistaken for brown recluses in Canada. While females will usually be found on their webs, males are often found out and about when searching for females. They all look pretty similar to the one pictured below, but see this post for more information house spiders and hobo spiders.

Eratigena atrica

Female giant house spider (Eratigena atrica – formerly Tegenaria duellica). These spiders are often mistaken for recluses, but note the pattern on the abdomen. Photo: Sean McCann.

3. Does it have stripy or spiky legs, or more than one colour on its abdomen?

Stripy_legs

Stripy legs + patterned abdomen = not a brown recluse. Photo: Sean McCann.

If you find a spider that has stripes or large spines on its legs, it is not a brown recluse. If it has a patterned abdomen, it is not a brown recluse.

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Stripy legs with large spines + patterned abdomen = not a brown recluse. Photo: Sean McCann.

Brown recluses have plain brown abdomens and plain brown legs with fine hair but no large spines.

4. Does it have extremely long and skinny legs?

Pholcus_phalangiodes

Cellar spider, Pholcus phalangiodes (family Pholcidae). The dark spot on the cephalothorax looks a bit like a violin,  but do not be fooled. This is not a brown recluse. Photo: Sean McCann

If it has extremely long skinny legs like the spider in the image above, it is a cellar spider (or daddy-longlegs), not a brown recluse. Despite looking very dissimilar to brown recluses, these spiders are often mistaken for brown recluses because of the “violin” mark on the back. Having a violin-shaped marking is not, by itself, a good way to determine if a spider is a brown recluse.

4. Is it really big? 

Brown recluses are not huge spiders. If its body length (not including legs) is more than 0.5 inches or about 1.25 cm, it’s definitely not a brown recluse.

5. Does it have 8 eyes? 

This is the dead giveaway, provided you are close enough to the spider to count its eyes. If it has 8 eyes (like most spiders), it is not a brown recluse. Below are some 8-eyed spiders that are sometimes mistaken for brown recluses.

Fishing spider

Fishing spider (family Pisauridae) actually a close relative of fishing spiders in the family Trechaleidae, with 8 eyes. Also see: stripy, spiky legs. Photo: Sean McCann.

 

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A wolf spider (family Lycosidae). Wolf spiders have 8 eyes and spines on the legs. Photo: Sean McCann.

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A sac spider (family Clubionidae) A ground spider (family Gnaphosidae, genus Drassodes). It looks a bit like a brown recluse, but again, has 8 eyes, some larger spines on the legs, and a dark stripe on the abdomen. Photo: Sean McCann.

 

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Huntsman spider (family Sparassidae). These spiders are fairly frequently mistaken for brown recluses. Note the 8 eyes in 2 rows, and spines and darker dots on the legs and abdomen. Photo: Sean McCann.

Update (12/06/2015): Another 8-eyed spider that can easily be mistaken for a brown recluse (and is common in the southern states) is the male southern house spider. It has a similar violin-like marking on the back, but several other features that distinguish it from brown recluses. The 8 eyes are all tightly clumped together, it has conspicuous spines on the legs, and its pedipalps (the two small leg-like appendages at the very front end of the spider) are extremely long and stick straight out in front of its face (compare to a male brown recluse spider here).

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Male southern house spider (Kukulcania hibernalis). Photo: Sam Heck, licensed under CC BY-NC 2.0.

Some other spiders that are not brown recluses, like the woodlouse hunter Dysdera crocata, also only have only 6 eyes, but they are arranged differently (not to mention D. crocata is red or pinkish or orangish in colour, not brown).

Dysdera crocata on white

Female woodlouse hunter, Dysdera crocata. Her 6 eyes are all in a tight bunch in the centre of the cephalothorax, and her massive fangs are much larger than those of a brown recluse. Also, these spiders are not brown. Photo: Sean McCann.

Brown recluses only have 6 eyes, arranged in 3 pairs.

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This is a brown recluse. It has only six eyes. Also note the fine hairs on the legs, but no spines, and the plain brown abdomen. Photo: Alex Wild, used with permission.

If you answered no to all those questions (or all but questions 1a and 1b and you’re really lucky!) AND the spider looks just like the one in the image above, then you’ve found a brown recluse. If not, then it’s another kind of spider that is totally harmless. (The only other medically significant spiders in North America are black widows). Either way, please remain calm. Spiders are not out to get you, and will leave you alone if you leave them alone. Here are some tips for avoiding brown recluse bites if you do live within their range. Still not sure about any of this? Please feel free to tweet at me (I’m @Cataranea on twitter) or comment here if you have any questions and I’ll be happy to try to answer them.

 

*I’ve also started answering this question on twitter with the hashtag #notabrownrecluse. This campaign, with the goal of educating people about the brown recluse spider, is a blatant ripoff of inspired by wildlife biologist David Steen (he’s @AlongsideWild on twitter), who tweets snake identifications using the hashtags #NotACottonmouth and #NotACopperhead. For more about his awesome twitter outreach, check out this excellent article: ‘This snake scientist is the best biologist on twitter‘.

**This guide is based on the following resources:

Vetter, Rick. (1999). Identifying and Misidentifying the Brown Recluse Spider. Dermatology Online Journal, 5(2). link

Vetter, Rick. (2009). How to Identify and Misidentify a Brown Recluse Spider. Web Resource. link

The truth about spider bites: “Aggressive” spiders and the threat to public health

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This post was written with Chris Buddle, and originally appeared on his blog Expiscor at Scilogs.com

Misinformation about spider bites is everywhere

Spiders are polarizing: people tend to be fascinated or fearful, and for some, Arachnophobia can be quite serious. However, spiders are often feared unnecessarily. They are quickly blamed for almost ALL unexplained bites or lesions!

It doesn’t help that there is an incredible amount of misinformation and fear-mongering related to spiders in the popular media and all over the internet. What’s worse, misinformation about spiders also appears in the medical literature. For example, the journal Emergency Medicine recently published an article on bites and stings that made the following claims:

“The [hobo spider] is considered aggressive and tends to bite even with only mild provocation. The clinical presentation, inclusive of systemic reactions, is similar to that of the brown recluse spider.”

This got us all riled up, and we decided to set the facts straight:

1. The hobo spider is not aggressive.

Here I am, holding an “aggressive” hobo spider. Photo S. McCann.

Exhibit A (photo, right): the allegedly aggressive hobo spider. This female hobo was minding her own business on her webuntil being rudely removed to a human hand and made to pose for photographs.

As for its supposed tendency to bite when provoked, Samantha Vibert, an arachnologist at Simon Fraser University says,

“During my PhD, I’ve studied the ecology and courtship behaviour of the hobo spider, Eratigena agrestis. This work entailed surveying dense populations of the hobo spider in the field and conducting experiments in the lab. Over the course of several years, I’ve handled hundreds of hobo spiders. I am always puzzled when I hear the hobo spider described as an “aggressive” species. Their one and only strategy when disturbed is to run away. The only mildly disturbing thing about them is the speed with which they bolt! When they feel threatened, they’ll abandon their web and make a dash for the nearest dark corner. I can only assume that their bad reputation stems from 1) a misunderstanding of their scientific name (agrestis means “of the field”, and not “aggressive”) and 2) their appearance. For people who dislike spiders, their relatively large size and long legs are not endearing. In fact, this spider is very meek and gentle but sadly misunderstood!”

2. The evidence that hobo spiders cause dermonecrotic lesions is poor and largely circumstantial.

Hobo spiders are European, but they were introduced to North America in the early 20th century and have since become established in the northwestern US and British Columbia, Canada. Hobo spiders live peacefully alongside humans in Europe, where nobody seems to be all that concerned about them. A 2001 study found no support for the hypothesis that the venom of North American hobo spiders differed from that of their European counterparts in its ability to cause necrosis. Most of the evidence tying hobo spiders to dermonecrotic lesions in medical case studies is weak and circumstantial. For example, the mere presence of this species in the house or even the neighbourhood where the supposed bite victim lived has been used to implicate hobo spiders. There only seems to be one case reported in the medical literature with reasonably incriminating evidence – the dead spider was found crushed under a pant cuff. But even in this case, the person had a pre-existing medical condition and did not seek medical attention for more than 2 months after the bite, casting doubt on whether the spider’s venom was actually responsible for necrosis.

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A female hobo spider. Photo by S. McCann.

3. Spider bites are extremely rare, and often misdiagnosed.

It is disappointing to see these myths about spiders propagated among some doctors and the public, but more importantly, it is dangerous. Here is a list of some of the actual conditions that have been misdiagnosed as resulting from spider bites:

  • infections (bacterial, viral, and fungal)
  • cancers (basal cell carcinoma and lymphoma)
  • poison oak and ivy
  • burns
  • Lyme disease (resulting from tick bites)
  • vascular disorders
  • pyoderma gangrenosum

Arachnologists Robb Bennett and Rick Vetter advise doctors that,

“The criterion standard for spider-bite diagnosis should be a spider caught in the act of biting or otherwise reliably associated with a lesion (and properly identified by a qualified arachnologist). Unless this standard is met, a working diagnosis of a spider bite should not be considered. Any of the above conditions are more likely.”

In spite of there being no brown recluses in Canada, it is common to hear about people who have been diagnosed with brown recluse bites here. Most of these folks never saw a spider or felt a bite, but had their mysterious lesion diagnosed as a spider bite by their doctor, who they trust as an expert. This comic nicely sums up why the vast majority of the time, it is safe to assume that a spider did not bite you.

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The poor brown recluse is always getting blamed for unexplained lesions. Photo by M. Bertone, reproduced here with permission.

Even where there are brown recluse spiders, they hardly ever bite people. There was a family home in Kansas that had 2,055 brown recluse spiders collected from it over a 6-month period, and no one living in the house got bitten. Still not convinced? In Florida, medical professionals diagnosed 124 brown recluse bites over 6 years. That’s 124 people who accidentally got near enough to the alleged spiders to be bitten, while going about their everyday business (only one of them ever produced an actual brown recluse for identification). Arachnologists – we’re talking people who actively go around seeking outspiders in likely spots – found only 5 brown recluses in Florida over the same 6-year period and a total of only 70 brown recluse spiders over 100 years. The numbers simply do not add up.

Did we mention that spiders hardly ever bite people?

Sometimes spiders do bite people, and a few species are legitimately considered medically significant. In North America, black widows as well as brown recluse bites are serious and certainly may require medical attention. However, black widows in particular have an undeserved bad reputation. They are not aggressive, rarely bite, and even when they do, they often don’t inject any venom. Most news articles about black widows refer to them at least once as deadly – often in the headline. According to the American Association of Poison Control Centers, 2,246 black widow bites occurred in all of the United Stated in 2012 (that doesn’t mean they were verified as actual black widow bites, just that they got reported, so this is almost certainly an overestimate). Only 21 of these reported bites resulted in major, but non-lifethreatening, symptoms, and no one died. Compare those zero deaths with the 36,166 traffic fatalities in the US in 2012. Cars are not regularly described as deadly but perhaps they should be. It would be more reasonable to fear automobiles than black widows. Arachnophobia is of course a legitimate condition, but there really are a lot of worse things to worry about.

A black widow, photographed by S. McCann.

4. There are serious consequences of spider bite misinformation and misdiagnosis

Assuming every unknown lesion is a spider bite can prevent accurate diagnosis, and delay proper treatment. Inappropriate treatment based on the misdiagnosis may be ineffective or worse, harmful. Overzealous diagnoses of spider bites can also lead to arachnophobia and reckless, unwarranted attempts to rid homes of spiders. Unnecessary exposure to pesticides is probably much riskier than sharing your home with spiders.

In sum, we hope this post is seen as a “Public Service Announcement” (or better yet, a “Public Spider Announcement”) and that we can help dispel some myths about spiders. We should be celebrating their incredible biology and natural history, and we should look to spiders as our allies in controlling pest insects, or taking down mosquitoes.

We should look at spiders in awe, rather than in fear.