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This question is prompted by Snake on Chest While Sleeping?. In this question, the OP asked what to do if he wakes up in his tent in his sleeping bag to find a snake on his chest. (Note: this was not presented as merely a "world building" hypothesis. OP claimed to know of such occurrences.)

In that question, there is some discussion about how likely it is that the snake is venomous. There is no discussion about how you figure out if the snake is venomous. (Particularly in the dim light inside a tent during the hours when you are sleeping!)

Thus, my question: Assuming you have the presence of mind to remain utterly still while you figure out whether the snake is venomous, how do you make this determination?

Some of you may be familiar with the very local NextDoor network. In discussions there (my locale has copperheads), much is made of the shape of the head. If its head is triangular, it's venomous; if not, not. Is this correct? Always correct? Correct anywhere? (Please don't focus on copperheads.)

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    Let it bite you and your confidence goes up, but that is not a great option. Learning to identify the snakes in your normal haunts is easy, expeditions to another continent not so much.
    – Jon Custer
    Oct 13 at 0:41
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Yes, and no.


There is certainly a tendency towards the more triangular/bulbous head of a snake indicating that it's venomous. However, there are significant outliers to that rule (notably, the Inland Tiapan, for example, which is the most venomous snake in the world!)

Inland Tiapan with non-triangular head, source: https://10mosttoday.com/10-most-venomous-snakes-in-the-world/

On the other hand, snakes like the grass snake, smooth snake, and viperine snake are nonvenomous and can mimic the classic triangular head shape.


Unfortunately, you will be better served by educating yourself on the venomous snakes located in the area you are traveling than by having one rule of thumb.

It also depends on exactly where you are. In some regions, you can potentially rely on head shape, but there can be false positives (as noted above with snakes that mimic their venomous relatives. As you can see below, even some graphics that do state the head shape rule of thumb include exceptions. So, know the wildife where you're traveling if you want to have the best chances of properly identifying a snake. And if you're not sure, every snake is venomous.

Image of snake head shape, with Brown Watersnakes as a triangular-headed nonvenomous exception, and the Coralsnake as a smooth-headed venomous exception

Rattlesnakes, however, are universally venomous, so you can have that at least.

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  • Why the comment about rattlers? Oct 13 at 15:19
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    @RoddyoftheFrozenPeas Presumably because if a snake starts rattling at you, then it's going to be venomous.
    – user
    Oct 13 at 16:55
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    @RoddyoftheFrozenPeas the OP was asking about identifying venomous snakes, and how accurate you can be with identifying features. If it has a rattle, it’s venomous. Unlike the head shape or other features, you can be confident of positive identification with a rattle. That doesn't say anything about snakes without rattles, though. Only that rattle ⇒ venom. Oct 13 at 17:46
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    Snakes that spit at you are another easy ‘always venomous’ one. Though usually if they’re spitting at you, it’s too late for it to matter, just hope the venom doesn’t get in your eyes. Oct 13 at 18:06
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    @fyrepenguin Some non-venomous snakes will shake their tails against the ground or dried leaves to mimic rattlesnakes. Some of them could plausibly pass for rattlesnakes, especially if you're not super familiar with rattlesnakes. (They are highly motivated. The more convincing their rattlesnake impression is, the less likely a predator will try to eat them.) They will also puff out their head to make their head look more triangular. Oct 14 at 18:17
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Perhaps for a certain region, but not universally.

When you are looking at only a certain region, then there might be some visible characteristic all the common venomous snakes just happen to have in common. But that is usually a coincidence, not a characteristic inherently linked to whether or not it's venomous. So rules like "avoid snakes with triangular heads" or "red touch yellow kills a fellow, red touch black, venom lack." are usually only useful in very specific regions. You can not expect a rule which was coined in one region of the world to be of any use in an entirely different region. There will be other snakes there, which will require to remember other characteristics.

Also keep in mind that global warming leads to species migration in a lot of regions of the world, so a particularly old rule might no longer be applicable today.

Bottom-line: Before you engage in outdoor activity in an unfamiliar region, do your homework about which animals are dangerous there and how to recognize them!

And anyway, it is generally a good idea to treat every snake you encounter with respect, dangerous or not. Not just for your own safety, but also to avoid unnecessary disturbances to wildlife in its natural habitat.

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  • +1 Good points. Thanks for mentioning possible migration because of warming.
    – ab2
    Oct 13 at 22:04
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Anecdotal, I occasionally have all of the four venomous snakes of the US in my yard from time to time. The behavior of the venomous snakes is different from other snakes; they are calm and deliberate in their movement. I think they have self confidence. The copperheads, rattlers, and cotton mouths do not startle and zoom away like non-venomous snakes. The coral snake behavior is intermediate, they leave but not in a panic. The one timber rattler I met, I touched with a rake - no movement - I steadily squirted him with the hose and he slowly went away. Cotton mouths near my pond require significant encouragement to leave. Copper heads, which are common, casually move off when they see a person, which corals do as well, but faster. Non-venomous snakes disappear before I can identify them. I forgot an exception; Diamondback Water Snake. One was in my little pond ( 5' X 10') , he was not in a hurry to go and slowly went into some rocks, I never saw him again. He just looked like a snake not to mess with.

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  • +1 This is encouraging! So if I twitch, the nonvenomous snake will hurry away and the venomous snake will just shrug! I hope I never have to test this, though!
    – ab2
    Oct 13 at 21:54
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    @ab2 I would caution against assuming that as a general rule, however. Oct 13 at 22:39
  • Where do you live? I don't think I have such a variety (I'm in a built-up suburb of Dallas, but one that includes the occasional sign warning of venomous snakes in the area).
    – Flydog57
    Oct 14 at 0:14
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    @Flydog57 if I had to guess, I’d say they’re probably in the southeastern US. Though as a side note, “all of the four venomous snakes of the US” is a bit inaccurate. There may be four main types of venomous snakes in the US, but there are far more than four species (more in the range of 40) Oct 14 at 1:02
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    Actually there are only two types of venomous snakes in the US. Pit vipers, and coral snakes. the pit vipers are the rattlers, cotton mouths, and copperheads. They share the triangle head, slitty cat eyes, a blunt tail, and pits behind the nostril on either side of the head. Oct 14 at 16:02
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Assume any snake on your chest when you wake up is venomous and then when it's dead, examine it further. Erring on the side of caution gives you a great camping story. Assuming they are all safe, and being wrong, serves as a cautionary tale for other people.

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    What do you mean with "when it's dead"? Do you propose to kill any animal which gets too close to you? Lethal violence should be the last resort, not the first, when dealing with a potentially dangerous animal.
    – Philipp
    Oct 14 at 7:47
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    @Philipp: I think they meant to slowly take a hatchet (or a rifle) and aim at the snake that is resting on your chest, and BAM! The snake is dead. If you are still alive you can do the examination. As a famous philosopher said "it is when the mosquito lands on your testicles that you realize that violence is not the answer to everything"
    – WoJ
    Oct 14 at 16:15
  • +1 Seems to be the only vaid assumption!
    – ab2
    Oct 14 at 19:12
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    Assumption may be valid, but I do not agree with the suggested course of action. For one, successfully killing the snake sitting on your chest is not a given, and attempting is a great way to get bitten. Additionally, if it’s not a snake that’s directly threatening you, there’s no reason to kill it. Even then, most snakes are not particularly aggressive, so there’s usually not a reason to kill them at all. Oct 14 at 22:46
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Can you tell if a snake is venomous from casual examination?

Not really with certainty. Non-venomous snakes often mimic venomous varieties, because it's a lot safer to be venomous!

This non-venomous gopher snake looks exactly like a rattlesnake, especially with the tip of it's tail tucked up so you can't see it. It has bulged out it's cheeks so that it's head appears triangular, and it has assumed the confident striking pose as well. If snakes were eligible, this snake would get an Academy Award.

This non-venomous black snake is rattling it's tail against the ground and making a lot of noise. It doesn't sound precisely like a rattlesnake, but certainly close enough that you might think it was one--especially if you couldn't see the snake clearly.

The non-venomous scarlet king snake has a bright red-yellow-black striped pattern, almost exactly like the highly venomous coral snake. The primary difference is that the king snake has red-black-yellow-black stripes and the coral snake has red-yellow-black-yellow stripes...for the common species in North America. If you only get a glimpse of the snake or if you're more focused on running away, it's easy to mistake the two.

The exceptions are some harmless snakes which have very distinctive appearances that aren't shared by venomous snakes, such as ring-necked snakes (they are technically venomous, but it's only a problem if you're very, very small--like if you were about the size of a small frog or mouse). You can usually identify a ring-necked snake at a glance, but most snakes are not so easy.

Also, even a non-venomous snake bite can be unpleasant. The northern watersnake is not venomous, but it often looks like a copperhead and is notoriously short tempered and willing to bite. Even though their bite won't kill you, they can draw blood and generally make you unhappy. (Don't get between them and the water, it makes them feel threatened.)

The safest approach is to treat all snakes as though they will bite you and a bite will be unpleasant. Give them room when you can, and when you can't (such as you've woken up with one on your chest) move slowly and non-threateningly and let the snake depart of it's own accord. None of these snakes want to harm you or have anything to do with you--you are too big for them to eat.

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  • +1 Appreciate message that there are no easy answers!
    – ab2
    Oct 14 at 19:11

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