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This Snake Identification Pack can be used to identify snakes in your area as well as when you are researching these creatures.
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Wondering how to identify snake holes in your yard? Learn all you need to know in our guide about snake holes in the yard.
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Click here to view this post in Spanish! Haga clic aquí para ver este blog en español! I noticed that a huge proportion of the hits on this site are for the posts about identifying snake sheds (parts I and II), which I expect is a result of people searching for a key or guide to use to ID a snake shed that they have seen or found. Even though there is some useful information in those other posts, they are written more like detective stories with a particular conclusion in mind, and they certainly aren't comprehensive. Here, however, I've attempted to put together a more complete how-to guide on how to ID sheds of snakes found in the United States and Canada. One excellent free reference on this subject is an electronic pamphlet by Brian Gray called A Guide to the Reptiles of Erie County, Pennsylvania. Even if you don't live in Erie County, Brian's section on shed snake skins is a very useful guide to many of the common species found in the eastern United States, because it contains many excellent, high-resolution images of the scale characters, and it is organized as a dichotomous key: a series of questions, each with two choices, that inevitably leads to an identification (it's sort of like a choose-your-own-adventure book). Brian's more comprehensive book, The Serpent's Cast, is also an excellent resource, containing images of shed skins that have been painstakingly prepared for viewing the details of the scales necessary for identification to species. Although shed skins that you are trying to identify won't always be that cleanly preserved, often many of the identifying features are still visible. From Cardwell 2011; viper (top) and colubrid (bottom) The first thing that many readers will want to know will be whether or not the snake whose shed skin they have found is a venomous species. This distinction corresponds nicely with determining what family the snake is in. In most of North America, there are two families: Viperidae (vipers, which are venomous) and Colubridae (colubrids, which are not1). The easiest way to distinguish these two families by their shed skins is to locate the sub-caudal scales (the scales under the tail). Colubrids have a double row of scales under the tail, whereas vipers have a single row. This is a pretty invariant character2, especially near the anterior part of the tail, and it can help you tell the family of the snake whose shed you've found every time. Coral snakes, which are in the family Elapidae, also have a double row of scales under the tail, but if you think you have found a coral snake shed, post a pic because that's an amazingly lucky find. More about these, and a few other options, later. First, colubrids: Divided anal scale Single anal scale Once you have figured out the family, a second pair of characteristics can help you narrow down which genus of colubrid you might have. These are 1) the texture (smooth or keeled) of the dorsal scales (these are the relatively small scales that cover the snake's entire back and sides) and 2) the condition (single or divided) of the anal scale or anal plate (the scale covering the cloaca). Keeled dorsal scales have a ridge running down the center, whereas smooth dorsal scales have no ridge, like so: Smooth (left) and keeled (right) dorsal scales Using these characteristics in tandem should allow you to divide the colubrids in to four groups: single/smooth, divided/smooth, single/keeled, and divided/keeled. These are not taxonomic groups (that is, not all single/smooth snakes are each others' closest relatives), but they are useful for distinguishing genera of colubrids when all you have to go on is the shed skin. All North American vipers have keeled scales and a single anal scale, so these characters are less useful for distinguishing them, but more on these later. Most of the species of North American snake are colubrids (about 80%, or 105 of our 131 species). Here is a quick guide to the colubrids of the US and Canada, by dorsal and anal scale characteristics: A few genera are split among multiple categories: Gyalopion because G. quadrangulare has a single anal scale whereas G. canum has a divided anal scale, and Opheodrys and Virginia because one species of each has keeled scales and the other has smooth (these are helpfully called Rough and Smooth Green and Earth Snakes, respectively). It's also worth noting that anal scales of Farancia are pretty variable, although your chances of finding a Farancia shed are slim (but see part I). As you can see, we are using the process of elimination to narrow down the possible candidate species for your shed. A quick look at the range maps in a regional field guide will allow you to cross off about half the genera on the above list, depending on where you live, probably leaving you with 2-6 possibilities. The overall size of the shed can also be of help, although keep in mind that large snakes are born small and that snake sheds stretch somewhat as they are removed. Still, many of the snakes on the above chart reach adult sizes of only 12-24", so they could potentially be eliminated on the basis of size. Width of the ventral scales can help too, because it gives you an idea of body shape, and this does not change as much during the shedding process. However, at this point, the most useful thing to do next is to look at another scale meristic. One that can help you distinguish among the several genera within each group requires counting the dorsal scale rows. Dorsal scales are arranged in rows, the number of which can be counted from left to right, like so: Three equally good ways to count dorsal scale rows (in C, scale 1 not shown). Modified from K. Jackson (2013) You'll want to start with the first dorsal in contact with a ventral on one side and proceed over the back and down the other side so that the last scale counted is the dorsal scale in contact with a ventral on the other side of the snake. Although the conventional way (A) is for this to be the same ventral scale as the one your first dorsal scale row was in contact with (that is, count in a ‘V’ shape, as depicted above, so that you are counting all the scales associated developmentally with a single pair of ribs), you should get the same result even if your 'V' is asymmetrical (B), or even if you count in a straight line (C), which can be easier since you don't have to decide where to change direction on the 'V'. Often it doesn't matter, although it's worth noting that in some snakes the number of dorsal scale rows varies along the length of the snake. The best way to guard against this is to count a row in the middle of the body, which is the number meant if only one is given in most keys. More often, you will see numbers of dorsal scale rows given in the format “15-17-15”, indicating the number of dorsal scale rows at three places on the body (in order): the neck, midbody, and a bit (about one head length) before the cloaca. In North America, you should almost always get odd numbers, and although these numbers can sometimes be fairly variable, combining them with decisions you made above based on the subcaudals, anal scale, dorsal texture, body size, and range should allow you to decide on a genus in almost 100% of cases. Here is a list of the dorsal scale formula ranges for the North American colubrids (remember, it's neck, midbody, and before the cloaca). Where ranges are given in parentheses, species within that genus have differing scale formulas. Where ranges are given without parentheses, there is regional or other variation within one or more of the species in that genus. In a few cases, only the scale row counts at midbody are given. Knowledge of the number, shape, and relative size of the head scales is usually necessary to distinguish among species within a genus (for example, to tell a Scarlet Kingsnake from a Mole Kingsnake), and unfortunately many sheds are missing their heads or the heads are in poor condition. Other clues can be obtained from pattern, which is often visible in good light, and from counting the total number of subcaudal or ventral scales (impossible if you only have a partial shed). If you have taken your shed to genus and want to send me pictures of the head for help identifying it to species, feel free. I would recommend using your digital camera's macro setting (almost all cameras have one, the symbol is a little flower) to photograph snake sheds. You can also find details of the head scalation of all species of North American snakes in the book Snakes of the United States and Canada by Ernst & Ernst, and much of this information is available online as well. It's often helpful to keep the shed in a Ziploc bag for later reference. I like to write on the bag with a Sharpie the date, location, and tentative ID of the snake. Non-colubrids As I mentioned above, all North American vipers have single subcaudals, keeled dorsal scales, and a single anal scale, so these characters are less useful for distinguishing them from one another. However, there are only three genera: Agkistrodon (Copperheads and Cottonmouths), which have no rattles, and two genera of rattlesnakes, Crotalus (which have small scales on the tops of their heads) and Sistrurus (which have large scales on their heads). Telling the different species of Crotalus by their sheds could be tricky, but unless you live in Arizona, there are usually only one or two options in any given location in the US. Size and pattern could also be helpful. Feel free to share pictures (remember to use macro). Copperhead and Cottonmouth sheds can be hard to distinguish, but range, size, and habitat can help, as well as the presence or absence of a loreal scale (the scale on the face between but not in contact with either the eye or the nostril), which Copperheads have and Cottonmouths do not. Micrurus fulvius If you live in certain parts of the US, there are a few other snakes that aren't colubrids or viperids whose sheds you might find. One familiar group is the elapids, represented in North America by the Coral Snakes. One species is found in Arizona and New Mexico, and the other in the southeastern coastal plain from Texas to North Carolina. I have never seen a Coral Snake shed, but I would imagine that the highly contrasting, distinctly banded pattern would be easily visible. However, these can also be distinguished by their scale characteristics: Micrurus fulvius has smooth dorsal scales in 15 rows and a divided anal plate, and Micruroides euryxanthus has smooth dorsal scales in a 17-15-15 pattern with a divided anal plate. The other US elapid, the Yellow-bellied Sea Snake (Pelamis platurus, found in the Pacific Ocean off southern California) sheds at sea, so unless you are in very unusual circumstances the sheds will not be found. They have smooth scales with a 39-47, 44-67, 33-46 row formula and a divided anal plate. Lichanura trivirgata If you live in southern California or the intermountain west, there are two species of temperate boids, the Rubber (Charina) and Rosy (Lichanura) Boas, whose sheds you could find. Boa sheds are very different from those of other snakes. Boas have small, round dorsal scales that are very numerous - Charina and Lichanura have 32-53 and 33-49 dorsal scale rows, respectively, so you should be able to tell a boa shed by the small size and number of dorsal scales. Rubber Boas have blunt tails and specialized head scales, whereas Rosy Boas have long tails and unspecialized head scales, and their ranges do not overlap. If you live in southern Florida, you might find sheds of Boa Constrictors or Burmese Pythons, which you should be able to tell by their huge size, or any number of other exotic snakes (good luck with those). Rena humilis Finally, the southwestern US is home to several species of scolecophidian blindsnakes in the genera Rena and Leptotyphlops. These are tiny and have undifferentiated body scales, meaning that all scale rows around the entire body (including the underside) are the same width. They are iridescent and extremely difficult to count, which has given rise to one of my all-time favorite quotes from a scientific paper: "We castigate the ancient lineage that begat Liotyphlops, for it is obviously the worst designed snake from which to obtain systematic data" (Dixon & Kofron 1983). An additional species, Ramphotyphlops braminus, is introduced in Florida, Louisiana, and Hawaii, as well as in many other locations around the world (it's parthenogenetic and so a really good invader because it only takes one!). Blindsnakes shed their skins in a series of rings rather than in a single piece, and they are so small that any sheds found would be unlikely to belong to any other kind of snake and so fairly easy to identify. Feel free to comment or email with questions or photographs. Happy herping! 1 I am making a distinction between North American snakes that are dangerously venomous to humans (vipers & coralsnakes) and those that aren't (colubrids). Although some species of colubrid snake possess deadly venom, such as boomslangs and twigsnakes, these are not native to North America. Other colubrids, including some North American species such as Hog-nosed Snakes (Heterodon), are venomous in the sense that their Duvernoy's gland secretions are toxic to their prey, but are harmless or nearly so to humans. For a very thorough discussion of this issue, check out the book "Venomous" Bites from Non-Venomous Snakes. ↩ 2 Long-nosed Snakes in the genus Rhinocheilus can have a mixture of divided & undivided subcaudal scales. ↩ ACKNOWLEDGMENTS Thanks to Brian Gray, Jack Goldfarb, and JD Willson for their excellent photographs. REFERENCES Cardwell MD (2011) Recognizing Dangerous Snakes in the United States and Canada: A Novel 3-Step Identification Method. Wilderness & Environmental Medicine 22:304-308. Dixon JR, Kofron CP (1983) The Central and South American anomalepid snakes of the genus Liotyphlops. Amphibia-Reptilia 4:2-4. Ernst CH, Ernst EM (2003) Snakes of the United States and Canada. Smithsonian Institution Press, Washington D.C. Gray BS (2011) A Guide to the Reptiles of Erie County, Pennsylvania. Natural History Museum at the Tom Ridge Environmental Center, Erie, Pennsylvania. Weinstein SA, Warrell DA, White J, Keyler DE (2011) "Venomous" Bites from Non-Venomous Snakes: A Critical Analysis of Risk and Management of "Colubrid" Snake Bites. Elsevier, Amsterdam. Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
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Click here to read this article in Spanish! Haga clic aquí para leer este artículo en español! Many people live in fear of snakes, especially of venomous species that can inflict a lethal bite. There is evidence that our fear of snakes is innate, because our ancestors have been preyed upon by them for millions of years, even before we were primates. Other evidence suggests a significant learned component to ophidiophobia. Either way, few people today are at risk of being eaten by snakes, but bites from venomous snakes are still fairly common. However, in my experience fear of snakes is way out of proportion to the actual risk they pose, especially among my fellow North Americans. It's surprisingly hard to find good information on the prevalence of venomous snakebite (hereafter, just 'snakebite'), but it's getting easier, and I was able to gather almost 100 papers that include data on the subject, which I've synthesized here. As a result, this article has many footnotes, and because I used so many references to prepare this article I've provided a selected list at the end of this post, with a link to the full list. Map of snake envenomings per year, from Wikimedia Commons So how dangerous is a snake bite? If you're bitten by the wrong kind of snake and you're far from help, it's pretty dangerous. But the truth about snakebite is that it's a lot less likely to endanger your life than people think. First of all, you're pretty unlikely to ever get bitten. Worldwide, estimates range from 1.2 million to 5.5 million snakebites annually. Remember, there are several billion people out there, so although those numbers are large, each year over 99.92% of people are not bitten by a venomous snake. These bites result in 420,000-1.8 million envenomings leading to 20,000-94,000 deaths. This probably seems really low, until you realize that unlike when they are biting their prey, snakes that are biting in defense don't inject venom every time (i.e., the bite is "dry"). Depending on the species of snake and the context of the bite, estimates for dry bites range from 8% to more than 80%, with North American rattlesnakes, one of the best studied groups, injecting venom only 20-25% [edit 10/23/2015: I made a mistake here. The source cites two other sources that say that rattlensakes inject venom 75-80% of the time (i.e., 20-25% dry bites), not the other way around as I originally wrote. But, Hayes goes on to say that neither of these sources appear to be based on empirical data, and then he gives some other sources that do. These list rattlesnake and other viper dry bite percentages between 7 and 43% (i.e., injecting venom 57-93% of the time). So, indeed, much higher than the 20-25% I originally listed, but still less than for predatory strikes. I apologize for the error.] of the time when biting in defense, compared to more than 99% of the time for predatory strikes.1 This behavior is partly because the strike itself may startle attacker sufficiently and wasting expensive venom needed to eat is useless, and partly because even injecting venom into an attacker is unlikely to immediately incapacitate it. Most snake venom is fast-acting, but it's not that fast. As a result of these dry bites, a lot of snakebites go untreated and unreported because they fail to produce symptoms, leading the bitten person to assume (correctly) that they are safe or (incorrectly) that the snake was not venomous. This is one major cause of the wide range of numbers given above for the prevalence of snakebite. Copperheads (Agkistrodon contortrix) bite a few hundred people a year in my home state of North Carolina, more than in any other state. Fatalities are exceedingly uncommon. Worldwide, about 1 out of every 20 people envenomated by venomous snakes dies from the bite, according to the best available estimates for the prevalence of bites and resulting deaths between 1985 and 2008. Depending on where you live, your chances of surviving a venomous snakebite are really good, although in a few places they're pretty bad. I'm going to focus on the USA because I live here and because we have some of the best data. In the USA, only 1 out of every 500 people bitten by a venomous snake dies as a result, which includes deaths from bites that take place under several special circumstances that we'll discuss later. You're actually safer from venomous snakebite in the USA than in any other country on Earth where venomous snakes kill people, thanks to our excellent medical care, relatively benign venomous snake fauna, and large proportion of the population that live in urban areas where venomous snakes are scarce. There are some countries, such as Canada2 and Norway, where venomous snakebites occur but nobody has apparently been killed by one in recent history, except for people who have been killed by their exotic, captive snakes (more on this later). Western Diamondback Rattlesnakes (Crotalus atrox) are large and widespread in the southwestern USA. Contrary to the popular myth, a recent study showed that larger rattlesnakes cause more serious bites than smaller ones, which makes sense because they have more venom to inject (see also unpublished data from the Hayes lab at Loma Linda University showing the same trend and also that smaller bite victims have more serious bites). How about all the people who are bitten and survive? Being bitten by a venomous snake isn't exactly a pleasant experience. It's been described as feeling like “hitting your thumb with a hammer”, “stepping on a bare electrical wire”, or “being repeatedly stabbed with a knife”. This alone is a good enough reason to avoid snakebite. However, not every venomous snakebite is a recipe for a nightmare. In the USA, most people are bitten by pit vipers (copperheads, cottonmouths, and rattlesnakes). Very few people are bitten by coralsnakes, and I'd be surprised if anyone has ever been bitten by a coralsnake that they didn't first pick up. Pit vipers are generally pretty retiring snakes, a fact observed most poignantly by both the herpetologist Clifford Pope, who called them first cowards, then bluffers, then warriors, and also by Ben Franklin, who wrote of a rattlesnake: "She never begins an attack, nor, when once engaged, ever surrenders...she never wounds 'till she has generously given notice, even to her enemy, and cautioned him against the danger of treading on her." Figure from Gibbons & Dorcas (2002) In a field test of these famous anecdotes, Whit Gibbons and Mike Dorcas molested 45 wild cottonmouths (Agkistrodon piscivorus) in South Carolina swamps and found that only 2 in 5 bit their fake hand when picked up, only 1 in 10 bit a fake foot when it stepped on them, and none bit a false leg that stood beside them. In a similar test, Xav Glaudas and colleagues picked up over 335 pigmy rattlesnakes (Sistrurus miliarius) in Florida and found that only 8% bit the thick glove they were wearing. Further evidence to support the fact that vipers are reluctant to bite potential predators comes from anecdotes from snake biologists radio-tracking snakes to study their spatial ecology, in which the biologist has accidentally stood on Timber and Eastern Diamondback Rattlesnakes and Puff Adders without provoking any responses. This makes sense because striking is a last resort for these snakes, which have a lot to lose and very little to gain by it. Although this isn't a perfect simulation of a typical snake-human interaction (these researchers weren't trying to kill the snakes in their experiments, after all), these findings are a good argument in the snakes' defense - if they bite you, they probably had a good reason. Russell's Vipers (Daboia russelii) are probably one of the world's most dangerous snakes, combining a relatively aggressive demeanor and relatively potent venom with a habitat and geographic range that overlaps areas of very dense, rural human population in south Asia. Although the above news is hopeful, it is of course impossible to predict whether an individual snakebite will end in tragedy, so it is prudent to avoid snakebite at all costs. Each year in the USA, between 2,400 and 4,700 (edit: some sources say up to 8,000) bites occur, putting your chances of being bitten by a venomous snake in the USA at about 1 in 100,000 (1 in 40,000 with higher bite estimate).3 If you live in southern or southeastern Asia, you're more justified in having a fear of snakes. In India, at least 80,000 and possibly as many as 165,000 people are bitten by snakes each year (1 in 7,000-14,000). India's venomous snake fauna isn't that much more diverse than the USA's, but medical care isn't as good, and it has about 4 times as many people, many of whom live in rural areas and work in agricultural or pastoral professions, both of which really increase your chances of being bitten. Even in India, "only" about 10,000-15,000 people a year die from snakebite (edit: a more recent study that estimated snakebite mortality in India using household surveys instead of hospital records came up with a figure of ~46,000 deaths in 2005, which is probably more accurate because many victims elect to use traditional therapy in their village and most do not die in government hospitals, where the data are collected; for a more thoughtful discourse on snakebite in India, click here), meaning that about 4 out of 5 (edit: using the newer data, between 1 in 4 and 1 in 2) snakebite victims survive. Taking into account your chances of being bitten and your chances of dying from the bite, many countries in sub-Saharan Africa, Asia, and Latin America are risky places to live. Snakebite in these places is a legitimate public health concern. The USA is the least risky country in terms of snakebite. The only safer countries are places like Ireland, New Zealand, Madagascar, and oceanic islands in the Pacific & Caribbean, where no venomous snakes occur. Snakebite risk in the USA is thousands of times lower than it is in many parts of the world, and it would be even lower if people modified their behavior in a few key ways, starting with not attempting to kill every snake they see. The USA (bottom left) is the safest country in the world in terms of snakebite risk. Countries without any venomous snakes not shown. Data from Kasturiratne et al. 2008 Click for larger version You might be surprised to hear that attempting to kill venomous snakes actually increases your risk of snakebite. This masterful post written by David Steen at Living Alongside Wildlife is a good argument for why this is the case. Specifically, the reason is that up to 2/3rds of snakebites in the USA are a direct result of intentional exposure to the snake and could be avoided if the people involved had made different decisions [Edit 16 May 2018: although recently, more well-replicated studies have shown that this figure is actually closer to 20% to 30%. Even so, I think it's safe to say that trying to catch a snake for any reason increases the chances that it will try to bite you. Killing a snake from a distance, e.g. by shooting it, is of course not nearly as risky from a snakebite perspective, but there are other associated risks and plenty of good reasons not to do that.]. These bites resulted from people who were trying to kill snakes or molest them, or who chose to interact with them for some other reason (ranging from snake handling churches to collection for rattlesnake roundups). Although snakebite is an occupational hazard for some, such as zookeepers and herpetologists, the vast majority of Americans are at extremely low risk of snakebite. Black Mambas (Dendroaspis polylepis) are among Africa's most dangerous snakes, but they still kill fewer people than hippos or mosquitos Let's take a closer look at those 5 people a year who die from venomous snakebite in the USA. Not all of these people are hikers, fishermen, and gardeners who fall victim to 'legitimate' bites, as you might assume. This number includes deaths that result from a pair of special cases that deserve special attention. The first is people who keep exotic venomous snakes in captivity in their homes. Although this can be done safely, it isn't always, and it is a little unfair to group these cases in with 'legitimate' bites, envenomations, and deaths from native, wild venomous snakes. It inflates USA snakebite statistics because the risk is not evenly distributed among the entire population and it inflates death statistics because antivenom may not be available for these exotic snakes. About 1 of the 5 deaths each year in the USA can be attributed to these circumstances. The second special case, people who refuse or do not seek treatment after they are bitten, includes some of the bites that also fall under the first case, because some snake owners that keep snakes illegally may not seek treatment out of fear that they will be arrested, fined, or have their animals confiscated. This case also covers religious snake handlers proving their faith, which in many cases entails foregoing treatment. It's harder to put a finger on how many people die in the USA each year from untreated snakebites, but I think it's probably fair to say that most of those people got what was coming to them. Let's not overlook the role of alcohol in people's decisions to interact with venomous snakes: studies show that around 40% of snakebite victims have been drinking. Data on intentionality of exposure to snakes in developing countries is sparse, but I would be willing to bet that exposure in these places is much less intentional, as it once was in the USA. CroFab antivenom used to treat most snakebites in the USA Today in the USA, medical treatment for snakebite is so good (thanks to synthetic antivenoms with few side-effects), and research on snake venom has come so far (with much left to learn!), that there is little justification for the overblown fear bordering on hatred people have of snakes. Progress toward this same goal is being made by some really smart people researching the venom of snakes in developing countries in Africa, south Asia, and Latin America, and figuring out better ways to make antivenom available outside of a hospital setting. Yet more than 1 in 20 people in the USA have a pathological fear of snakes, as defined by criteria including uncontrollable, greater than justified, and significantly interferes with a person’s routine, occupational or academic functioning, or social activities or relationships. Leading to situations like this recent news story and this bizarre interaction between a man, a gun, and a snake. Risk perception is influenced by many things, including the rarity of the event, how much control people think they have, the adverseness of the outcomes, and whether the risk is voluntarily or not. For example, people in the United States underestimate the risks associated with having a handgun at home by 100-fold, and overestimate the risks of living close to a nuclear reactor by 10-fold. Ironically, evidence suggests that two of these things (how much control you have and how voluntary the risk is) are actually quite high for snakebite, despite popular perception that they are low. Eastern Brown Snakes (Pseudonaja textilis) are one of Australia's more dangerous snakes, but even they won't chase, bite, or attack people without trying to escape or bluff first. Australia's low population density also contributes to their low prevalence of snakebite. Data on fear of snakes in developing countries is lacking, and it is difficult to generalize, but based on the impressions of several people I know who have lived and worked there, most inhabitants of rural areas in developing countries are terrified of snakes. One notable exception is Madagascar, where no venomous snakes occur and it is fady to kill any snake (edit: although apparently superstitions still abound). In contrast, in Australia people seem to have a relatively high level of respect for snakes and don't seem to mess with them solely out of machismo the way they do in the USA. Venomous snakebites are relatively rare, which is remarkable considering that the majority of snakes in Australia are venomous. I heard a story recently about a newly-hired Australian CEO of an American mining company. When the new boss asked about the snake policy, the employees jokingly replied that it was "a No. 2 shovel". The Australian CEO was not amused, because at his previous company Down Under routinely relocated much more dangerous snakes at their job sites. He instituted a company-wide training program to teach safe venomous snake practices. These classes are also available to the general public in some areas, especially in southern Africa. As people and wildlife come to share more and more space, snake-human interactions are inevitable. The future of conservation will probably be in maximizing compatibility between humans and wildlife rather than preserving pristine areas, we will need to get a lot better about behaving ourselves to keep ourselves safe from the defense mechanisms of wildlife, starting with educating ourselves about the real risks that underlie our fears. Everyone should read these guidelines for snakebite prevention and first aid. I would add to this: don't kill snakes! It only puts you at risk. Don't try to kill them, don't let your friends kill them, don't let your family members kill them. They won't try to kill you. I promise. For more about snakebite research and treatment, check out Dr. Leslie Boyer's blog and Bill Hayes's snakebite research page. 1 Venomous snakes that are striking at their prey practically always inject venom, and some evidence suggests that they can precisely meter their venom so that they inject exactly the right amount needed to kill each particular prey item, based on its mass. Fortunately for humans, there are no venomous snakes large enough to consider us prey. Dry bites to humans may result from the snake's deliberate decision to withhold venom or from kinematic constraints that reduce the duration and coordination of fang contact when striking a large, vertical object.↩ 2 Although global snakebite statistics frequently list 0 fatalities out of 200-300 snakebites for Canada, this seems not to be quite accurate. In Ontario, at least two people have been killed by Timber Rattlesnakes (Crotalus horridus), a soldier who was bitten at the battle of Lundy's Lane near Niagara Falls in 1814, and an American Indian chief prior to 1850. Two or three people have been killed by bites from Massasaugas (Sistrurus catenatus) in Ontario, all before 1962, and between 0 and 10 people were bitten annually from 1971-2007, mostly men aged 10-29. In 1981, a man who was "quite intoxicated" was killed by a bite from a Northern Pacific Rattlesnake (Crotalus oreganus) on the Nk’meep reserve near the town of Osoyoos in British Columbia's Okanagan Valley. He was the first person to be bitten by a native venomous snake in BC in over 50 years. The only other Canadian provinces that are home to venomous snakes are the Prairie Provinces of Alberta and Saskatchewan, where no recorded deaths have occurred from Prairie Rattlesnake (Crotalus viridis) bites. So we can conclude that native snakebites in modern Canada are even more infrequent than but follow the same basic pattern as those in the USA.↩ 3 In the US, relative to dying from heart disease (1 in 5), cancer (1 in 7), in a motor vehicle accident (1 in 80), in a fall (1 in 185), from a gunshot (1 in 300), by drowning (1 in 1100), by choking (1 in 4400), from drinking too much alcohol (1 in 10,900), by a sting from a wasp, bee, or hornet (1 in 63,000), from being struck by lightning (1 in 80,000), from a dog bite (1 in 120,000), or in an earthquake (1 in 150,000), you are very unlikely to be killed by a snake (1 in 480,000). The only less-likely causes of death are being trapped in a low-oxygen environment (1 in 548,000), being killed by ignition or melting of nightwear (1 in 767,000), and being bitten by a spider (1 in 960,000). These odds are for your entire lifetime; your annual chance of being killed by a venomous snake is more like 1 in 50 million. Worldwide, they're more like 1 in 200,000, which is a lot higher but still pretty low overall. ↩ ACKNOWLEDGMENTS Thanks to Julia Riley and James Baxter-Gilbert for providing me with information on deaths from snakebite in Canada, to Wes Anderson, James Van Dyke, and Xav Glaudas for sharing with me with their impressions of people's fear of snakes outside of North America, and to Matt Clancy, John Worthington-Hill, Larsa D., Todd Pierson, and Pierson Hill for the use of their photography. If you're so inclined, check out David Steen's post on why it doesn't make sense to kill venomous snakes in your yard here and Jessica Tingle's historical view of the subject here. SELECTED REFERENCES (click here for a longer list of references pertaining to snakebite [last updated February 2017]) Scientific illustrator Liz Nixon made this infographic featuring facts in this post! Click here for a larger version. Bellman, L., B. Hoffman, N. Levick, and K. Winkel. 2008. US snakebite mortality, 1979-2005. Journal of Medical Toxicology 4:43 Gibbons, J. W. and M. E. Dorcas. 2002. Defensive behavior of Cottonmouths (Agkistrodon piscivorus) toward humans. Copeia 2002:195-198 Glaudas, X., T. M. Farrell, and P. G. May. 2005. The defensive behavior of free–ranging pygmy rattlesnakes (Sistrurus miliarius). Copeia 2005:196-200 Hayes, W. K., S. S. Herbert, G. C. Rehling, and J. F. Gennaro. 2002. Factors that influence venom expenditure in viperids and other snake species during predator and defensive contexts. Pages 207-234 in G. W. Schuett, M. Höggren, M. E. Douglas, and H. W. Greene, editors. Biology of the Vipers. Eagle Mountain Publishers, Eagle Mountain, UT Isbell, L. A. 2006. Snakes as agents of evolutionary change in primate brains. Journal of Human Evolution 51:1-35 Janes Jr, D. N., S. P. Bush, and G. R. Kolluru. 2010. Large snake size suggests increased snakebite severity in patients bitten by rattlesnakes in southern California. Wilderness and Environmental Medicine 21:120-126 Juckett, G. and J. G. Hancox. 2002. Venomous snakebites in the United States: management review and update. America Family Physician 65:1367-1375 Kasturiratne, A., A. R. Wickremasinghe, N. de Silva, N. K. Gunawardena, A. Pathmeswaran, R. Premaratna, L. Savioli, D. G. Lalloo, and H. J. de Silva. 2008. The global burden of snakebite: a literature analysis and modelling based on regional estimates of envenoming and deaths. PLoS Medicine 5:e218 Morandi, N. and J. Williams. 1997. Snakebite injuries: contributing factors and intentionality of exposure. Wilderness and Environmental Medicine 8:152-155 Parrish, H. M. 1966. Incidence of treated snakebites in the United States. Public Health Reports 81:269-276 Ruha, A.-M., K. C. Kleinschmidt, S. Greene, M. B. Spyres, J. Brent, P. Wax, A. Padilla-Jones, and S. Campleman. 2017. The epidemiology, clinical course, and management of snakebites in the North American Snakebite Registry. Journal of Medical Toxicology 13:309-320. Swaroop, S. and B. Grab. 1954. Snakebite Mortality in the World. Bulletin of the World Health Organization 10:35-76 Tierney, K. J. and M. K. Connolly. 2013. A review of the evidence for a biological basis for snake fears in humans. The Psychological Record 63:919-928 Van Le, Q., L. A. Isbell, J. Matsumoto, M. Nguyen, E. Hori, R. S. Maior, C. Tomaz, A. H. Tran, T. Ono, and H. Nishijo. 2013. Pulvinar neurons reveal neurobiological evidence of past selection for rapid detection of snakes. Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1312648110 Walker, J. P. and R. L. Morrison. 2011. Current management of copperhead snakebite. Journal of the American College of Surgeons 212:470-474 Wasko, D. K. and S. G. Bullard. 2016. An Analysis of Media-Reported Venomous Snakebites in the United States, 2011-2013. Wilderness and Environmental Medicine 27:219-226.
Discover the hidden secrets: Unmask the snake's perfect hideouts! Learn how to spot potential hiding spots and stay one step ahead. Don't let them slither away!
