Tag Archives: venomous snakebites

Venomous Snakes of North America

This is the latest post in the Dangerous Animals series. Snakes cause some people to have a physical reaction of fear and revulsion, which is too bad as they are fascinating creatures. In many years as an educator about the natural world, I loved to use live snakes as examples. Many species can be safely handled and brought out with the public. They always create a stir among the viewers, some right up front with wide-eyed excitement, and others trying to appear casual while they move to the back of the crowd to let others get a good view.

I always respected the feelings of those folks who felt a bit uncomfortable, and ironically it was often the big, burly, macho males of the group for whatever reason. Numerous times in such situations I watched as the boy in class with great fear at first watched others touch the snake, with comments like “Oh, it is not slimy,” or “Wow, it feels cool,” and then slowly make his way to the front. It was always a great personal triumph when he screwed up his courage enough to tentatively reach out a finger to touch the snake and overcome some of his own demons.

As an aside, it also always upset me when I would see one spouse, usually the man, use one of the very realistic snake models we had to sneak up on his wife and scare her with it. That is not helping at all.

I think such fear is caused by a lack of understanding about these amazing creatures, and the knowledge that some of them are dangerous animals. That combination leads to lots of misinformation and confusion. The vast majority of snakes are harmless to humans, and all of them serve an important role in their ecosystems, being predators on small species helping to keep their numbers in check.

The venomous snakes of North America fall into two families: the vipers and the elapids. The vipers, more specifically pit vipers, include the copperhead (Agkistrodon contortrix), the cottonmouth (Agkistrodon piscivorus), and the rattlesnakes (about 30 species in the genera Crotalus and Sistrurus). The pit is a special heat-sensing organ located on either side of the head, between the eye and nostril, which allows the animal to track changes in temperature in its environment. This is most useful for tracking warm-blooded prey such as small rats at night, without needing light. In experiments, the snakes can be deprived of vision and a sense of small, and still stalk prey and strike with great accuracy.

Eastern Coral Snake

Eastern Coral Snake

The second group of venomous snakes belongs to the family Elapidae, the family that includes many deadly snakes such as cobras, sea snakes, and kraits. The coral snakes (Micrurus and Micruroides) are the New World representatives of this family. They live in three areas across the south. The eastern coral snakes lives in the Carolinas south to Florida. The Texas coral snake lives in Texas and Louisiana, and the Arizona coral snake lives in Arizona and extreme southern New Mexico. They are reclusive snakes, mostly living underground, are nonaggressive, and account for very few snakebites each year, which is a good thing because their venom is a very potent neurotoxin. Read more about venom here.

The copperhead is one of the most beautiful snakes in my opinion. They live in the eastern woodlands of North America, being found from Kansas and Oklahoma east through the southern and New England states.

copperhead

A copperhead snake, Agkistrodon contortrix, perhaps one of the most beautiful snakes in North America.

It can be found in northern Mexico in desert areas, but is closely associated with semipermanent water sources and riparian areas. It is a docile snake, and mostly relies on its coloration to keep it hidden. I have known hikers to step right over the snake without ever seeing it or having the snake react, which can also lead to bites when it gets stepped on directly. The venom of the copperhead is less toxic than the other pit vipers, and bites are generally less severe than from other venomous snakes.

There is a great deal of worry about the cottonmouth in the area that I grew up in, Ohio, which is ironic since they do not occur there. (I have observed this phenomenon over and over, with people being deathly afraid of species, having heard from so and so some horrific story about it, and just sure that they are of great concern when it does not even occur in the area. Humph.) They do occur across the southeast states, from extreme southern Virginia through Florida, and west to Oklahoma and central Texas.

Cottonmouth

Cottonmouth

The cottonmouth is closely related to the copperhead, but its temperament is not as docile. One of the reasons that this snake causes fear I think is because it can be hard to identify in the field if you are already predisposed to fear snakes. It is a heavy-bodied snake that is generally dark olive in color and resembles several species of harmless water snake. When threatened, the snake may open its mouth wide, flashing the white interior of its mouth as a warning, giving it the name cottonmouth. Its resemblance with several species of harmless snakes gives rise to far more “encounters” with cottonmouths being reported than actually occurs.

The rattlesnakes are a diverse group of snakes that only occur in the New World, and a species of rattlesnake occurs in every state in the contiguous United States expect for Maine. They do not live in Alaska or Hawaii. The largest native snake in North America is the eastern diamondback, which can reach over 7 feet long, although that is rare. (The indigo snake can be longer, but the eastern diamondback is heavier bodied.)

Timber Rattlesnake

Timber Rattlesnake

Their most obvious physical trait of rattlesnakes is the presence of the rattle, which is a modified string of scales on the end of the tail. The scales interlock in such a way as to allow the snake to shake its tail vigorously and cause the scales to rattle, giving notice to animals around it that it is there. As a warning system, it likely evolved so the snake could let large ungulates, that move in big herds, know that the snake was there specifically to avoid being stepped on. The snake most definitely would like to be left alone so it does NOT have to bite to defend itself. Listen to a rattlesnake here

Rattlesnakes would mostly like to avoid confrontations with humans too. When disturbed it will make its presence known and try to make a retreat. Some species are more likely than others to stand their ground and not flee. Bites most often occur when people fail to leave the snake alone, or surprise the snake unexpectedly, such as reaching under a log or into a rock crevice.

Venomous snakes do cause just over 5 deaths per year in North America (Langley 2005), and more bites that do not cause death, but injury and pain. (See this post for information about the number of bites each year). However, that number of fatalities and injuries caused by snakes pale in comparison with automobile deaths nationwide, with over 37,000 occurring in 2008. But automobiles are part of our everyday experience, which engenders a more blasé attitude generally than snake encounters.

Average number of deaths per year caused by various animals

Average number of deaths per year caused by various animals

Advice for outdoor adventures in areas where venomous snakes occur is pretty basic. Use common sense, be careful when around rocks and logs where you cannot see underneath, do not provoke any snakes encountered, and give the snake plenty of room to retreat. If a bite does occur, don’t panic and seek medical treatment right away. While a bite is a medical emergency, the modern antivenin available is very effective at mitigating snake venom

Langley, R. L. 2005. Animal-related fatalities in the United States–an update. Wilderness & Environmental Medicine 16:67-74.

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Venom, Poison, and Toxicity

There is a great deal of confusion about the terms venom, poison, and toxicity, and they are often used in an imprecise manner. However, the subject is great fun, so let’s explore it a bit.

First, we should clear up the difference between venom and poison. Venom is a substance that is generally injected, such as through a bite. Poison is something that is ingested, such as by eating or inhaling. So, these words relate to how the substance is gotten from point A to point B. Therefore, it is not correct to describe a snake as poisonous, unless it caused you some reaction if you ate it (beyond the thought of eating a snake, that is).

Dance Macabre

Dance Macabre

Monarch Butterflies, on the other hand, are poisonous. They take up toxic substances from the food source of the caterpillars, the milkweed plants, and by concentrating the toxins in their body, they become poisonous to consume. This is a defensive mechanism, not so much for the individual, but for the species as a whole. Any single individual might get eaten, but the effect on the eater is hoped to be so unpleasant as to cause it to not want to eat another one, so the entire species benefits.

Toxicity refers more to the effects of poison or venom. It is a descriptive term used to characterize the medical impact. So, venom can be more or less toxic and still be venom. All spiders are venomous (that is, they inject a venom), but not all spiders are equally toxic, and therefore dangerous, to people.

And, not to put too fine an edge on it, there are things that are toxic without being venom or poison. If you save up a bunch of your saliva, and then loaded it into a syringe and injected it into your skin, you would find that it has a toxic effect on the injection site. That is, the proteins in the saliva would begin to act upon the proteins in your tissues, but we hardly consider humans venomous.

Venom is found throughout the animal kingdom and serves a wide variety of purposes. Some of the most dangerous animals are venomous. Venom can help secure food, as in wasps that sting their victims to lay eggs upon for feeding the larva, or in shrews that bite their prey and inject venom to help immobilize it. Spiders, too, inject venom, which helps immobilize and kill they prey, but it also begins the digestive process so the spider can feed upon the liquefied remains.

Venom can be defensive. For example, a colony of honey bees does not need venom to feed, but uses it as a deterrent to would-be intruders on the hive. Fish, such as the lionfish, have spines with venom that can be injected into attackers upon being bitten. And the male duckbilled platypus has a spin on its hind legs that can inject venom, used again rival males in courtship combat.

Snakes are some of the best known, and most misunderstood, of the venomous animals, and snake venom is diverse in its function and toxicity. In general, snake venom falls into two broad categories: hemotoxic and neurotoxic, but in reality, most snakes have components of both.

Hemotoxic means that the components in the venom attack tissues, like in the spider example, such that the venom is breaking down the tissues of the victim in a pre-digestion process. Such venom can cause extensive damage to tissues, great pain, and cause death slowly over a period of time.

Neurotoxic venoms act upon the nerves system, disrupting the ability of the nerves to send and receive messages. The effect of this kind of venom is that critical nervous system signals stop, such as the signal to your lungs to breath, or to your heart to beat. This kind of venom can act very quickly to cause death.

The vipers, the rattlesnakes, copperheads, cottonmouth in North America, have venom that is mostly hemotoxic, with lesser amount of neurotoxic components. The elapids, the coral snake in North America, and its relatives like the cobras, have venom that is mostly neurotoxic.

So now you can be erudite at parties when friends say things like “Watch out, that black widow you are about to sit on it poisonous!” You can smile politely as you sit, and say “Actually, it is venomous. Let me tell you all about it.”

Related posts:
Venomous snakebites

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Number of venomous snakebites a year and pitfalls in scientific research

While doing a literature search for another story I encountered a classic pitfall in scientific research that one can all too often find. I wanted to know how many venomous snakebites occur each year, and of those, how many are fatal.

I dug into the literature to see what was there. My first stop was Wikipedia. With experience, I have learned that for science issues, Wikipedia is often very good. The wiki format mirrors the scientific publication process where contributors double check facts and each other, and on subjects that I know something about I find it to be a good general source.

I found a statement that there are approximately 7,000 – 8,000 people bitten by venomous snakes each year, and of those about 5 die. Even better, this statistic was given a reference (Henkel ?), as well it should. So, being curious about the original research, I looked up the citation. And here is where the pitfall begins.

In order to conduct science and add to human knowledge we must necessarily build on the work of others. One of the characteristics of science is that results must be repeatable—that is, in theory I could redo the work of any other scientist and get similar results. It is impractical for me to begin every research project by completely re-doing the work of all those researchers before me, so we cite their work and trust in it. (This also explains why scientists can be vicious anytime someone is caught fudging results—we have to be able to trust each other). However, sometimes you encounter what I will call the “chain of citations” pitfall.

copperhead

A copperhead snake, Agkistrodon contortrix, perhaps one of the most beautiful snakes in North America.

This pitfall is in the sloppy application of the scientific process, not with the process itself, and happens I guess out of laziness. It is where an author cites a point of fact from a research paper which may reference the fact (secondary source), but was not the paper where the research was presented in the first place (primary source).

I looked up Henkel and it turns out to be an interesting blurb from an appendix on safety, and he cites Gold et al. (2002), an article with the promising title “Bites of venomous snakes.” Ah, I think, here is the original research, so I look it up.

Those authors say “The true incidence of bites by venomous snakes in the United States is probably 7,000 to 8,000 per year, of which 5 or 6 result in death,” (pg 347) but they cite other authors for this fact, Langley and Morrow (1997).

This is getting silly, I think. How deep does this rabbit hole go? So I look up Langley and Morrow (1997).

The Langley and Morrow paper is a summary of deaths caused by animals of all kinds between 1979 through 1990. They compiled data from the US Department of Health and Human Services as published in Vital Statistics of the United States. They found that an average of 157 deaths occur each year as a result of injuries from animals, and about 60 of those came from venomous animals of all kinds, the majority being bees and wasps. They found an average of 5.5 deaths from venomous snakebites (Langley and Morrow 1997, table 2).

So, here at least we do have some original research on the number of fatalities each year. But how many bites? Langley and Morrow say “Approximately 45,000 snakebites occur each year, of which 8,000 are inflicted by venomous snakes,” (pg 12) and they cite Gold and Wingert 1994. Ok, let’s see what they say.

Gold and Wingert (1994) say “Approximately 45,000 snakebites occur in the United States each year. Poisonous snakes account for an estimated 8,000 of these bites, which result in approximately 9 to 15 fatalities,” (pg 579) and they cite Parrish (1966).

Finally, with Parrish (1966) we got to a paper that tries to determine not just the number of deaths from snakebites, but how many snakebites there are. Parrish (1966) conducted a survey of hospitals and physicians in both 1958 and 1959 to determine the number of snakebite victims treated. He sent questionnaires to a representative sample of both, and based upon the results, extrapolated to the total number of bites.

He wrote “On the basis of all these various reports, I estimate that approximately 6,680 persons in the United States (excluding Alaska and Hawaii [they don’t have venomous snakes]) were treated for poisonous snakebites during 1959,” (pg 272).

There are two numbers I cannot find in Parrish: 45,000 total snakebites and 8,000 venomous snakebites. I have no idea where these numbers originated since all the authors cite it, and all references point back to Parrish. Maybe the 45,000 number is a wild guess, and 8,000 is some adjustment to Parrish’s 6,680 number based on population growth? There is no way for me to know.

But this clearly shows the danger of relying on what the last guy reported and citing him as the authority when that is not what his paper was about. I tell my students to find the original publications and this is why. The number of deaths per year (about 5) is reasonably documented with the work of Langley and Morrow (1997), and in a more recent follow up study (Langley 2005). But, how many venomous snakebites occur in the United States in a year? Based on this evidence, we do not have a clue.

So here is a research tip, free of charge, to all you young budding scientists: go find the answer—just send me a copy of the results. Scour the literature to see if I missed something. Then, determine a good way to address the question and see if you can improve our understanding. The most recent data are over 40 years old, and inquiring minds want to know.

This post is in the dangerous animals series. Check out that post for more information.

Gold, B. S., and W. A. Wingert. 1994. Snake venom poisoning in the United States: A review of theapeutic practice. Southern Medical Journal 87(6):579-589.

Gold, B. S., R. C. Dart, and R. A. Barish. 2002. Bites of venomous snakes. New England Journal of Medicine 347(5):347-356.

Henkel, J.? For goodness snakes! Treating and preventing venomous bites. U.S.D.A. emergency response.

Langley, R. L. 2005. Animal-related fatalities in the United States–an update. Wilderness & Environmental Medicine 16:67-74.

Langley, R. L., and W. E. Morrow. 1997. Deaths resulting from animal attacks in the United States. Wilderness & Environmental Medicine 8(1):8-16.

Parrish, H. M. 1966. Incidence of treated snakebites in the United States. Public Health Report 81(3):269-276.

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