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What snakes are venomous/poisonous?

Table of Contents for this Hub Series on Snake Venom

  1. What snakes are venomous/poisonous?
  2. Snake Fangs 101
  3. Front- versus Rear-fanged Snakes
  4. Front- and Rear-fanged Snake Envenomation Systems
  5. Snake Venom Composition and Variability
  6. The Utility of Snake Venom Research
  7. The Expert's Guide to Snakebite

Venomous vs Poisonous Introduction/Summary Video

Common Characteristics of Poisons/Venoms

Table summarizing the most common ways to distinguish a poison from a venom. These are not all-inclusive, but are intended to serve as a quick-reference for separating the two kinds of animal toxins.

CharacteristicPoisonVenom

Created by:

Prey

Creature, itself

Stored in:

Body tissues

Glands

Used against:

Predators

#1:Prey, #2:Predators

Toxin delivered by:

Ingestion, absorption

Injection

Required mechanisms:

Toxin immunity, resistance

Fangs, stingers

Can be safely injected?

No

No

Can be safely ingested?

No

Yes

Can absorb through skin?

Yes

No

 

 

 

Poisonous Animal

A Cane Toad (Bufo marinus), showing the areas on the body that specifically store and secrete Bufotoxin: the Parotoid glands and the warts on the surface of the skin.  Some Bufotoxin is shown being expressed from the right Parotoid gland.

A Cane Toad (Bufo marinus), showing the areas on the body that specifically store and secrete Bufotoxin: the Parotoid glands and the warts on the surface of the skin. Some Bufotoxin is shown being expressed from the right Parotoid gland.

Is there a difference between a venom and a poison?

YES! There is! This is due to a number of factors (ref #1 and #4). First off, venoms are noxious compounds that are typically manufactured by the creature, itself, as opposed to poisons, which are most commonly sequestered from prey items (often from creatures near the bottom of the food chain, such as bacteria, beetles, and mushrooms).

Secondly, most venoms (at least, in snakes) have evolved primarily for offensive purposes (for use against prey) and only secondarily for defense (for use against predators), whereas poisons have evolved simply for defense (and are not used in the acquisition of prey). This approaches the nature of the toxins, themselves.

Third of all, venoms are toxic compounds designed to be introduced into the body tissues and circulatory/lymphatic systems of the prey or potential predator, meaning that in most cases, ingestion of such compounds would likely yield the complete breakdown of said toxins, resulting in minimal harm to the individual that consumed them (assuming there were no "leaks" in the digestive system of that individual, such as bleeding gums, sores, or ulcers).

Poisons are toxins specifically designed to be delivered into potential predators by way of ingestion or absorption (through the stomach, skin, mucous membranes, etc.), but are just as stable and dangerous if they are somehow injected into the flesh of a creature. Whereas venoms are localized in a compartment and are dependent upon complex physical mechanisms for injecting the toxins, poisons are commonly distributed throughout the skin and body tissues of the animal (typically with parts of the body storing differential amounts of toxins).

It is common for venomous or poisonous creatures to possess a high level of resistance/immunity to the toxins contained within their bodies (which partially explains how a rattlesnake can "accidentally" bite itself and not die). Can you be safely bitten from a poisonous animal, such as a Cane Toad? Generally, yes. Can you safely consume a venomous animal, such as a Western Diamondback Rattlesnake? Generally, yes. Now, there are exceptions to these "rules" which serve to create a blurry line between what defines a venom and a poison, but we will elaborate on some of those in the next section.

Venomous Animal

A Western Diamondback Rattlesnake (Crotalus atrox) having its venom extracted into a plastic beaker, emphasizing the front-fangs, venom, and venom gland (which is having pressure applied to it to aid venom extraction).

A Western Diamondback Rattlesnake (Crotalus atrox) having its venom extracted into a plastic beaker, emphasizing the front-fangs, venom, and venom gland (which is having pressure applied to it to aid venom extraction).

What snakes are venomous and which are poisonous?

Well, although the answer to that question can be relatively straightforward, there are a few special cases that must be discussed first. For instance, Spitting Cobras (Genera Naja and Hemachatus) are capable of launching their venom into the eyes of a potential predator, thus using their venom as a defensive poison instead, permitting the toxins to be absorbed through the eye's mucous membranes and causing blindness (among other envenomation symptoms).

This is not to say that other snake venoms applied to your eye will do no damage, as many of them will, it's just that Spitting Cobra venom (along with their fangs) has specifically evolved to be used for that defensive purpose (in addition to being used in the procurement of food via a venomous bite). This doesn't mean that Spitting Cobras can be considered "poisonous," though, since they can still be safely consumed.

However, certain species (and populations) of Garter Snakes (Genus Thamnophis, species sirtalis, couchii, and atratus) and one of their cousins (Tiger Keelback Snake, Rhabdophis tigrinus) are both venomous AND poisonous. How can this happen, you ask?

Simple: they produce their own venom in a specialized gland inside their upper lip (called the Duvernoy's gland) for use on prey, while retaining toxins from consumed prey in their body (Garter Snakes) or poison glands (Tiger Keelback Snake only) for use against predators.

Although Garter Snakes simply retain the poisons they acquire from newt prey (tetrodotoxin, abbreviated TTX) in their bodies for some time following a meal, Tiger Keelback snakes actively sequester the poisons they acquire from toad prey (bufotoxins, specifically bufadienolides) in a poison gland on the back of their neck (called the nuchal gland), enabling them to remain poisonous for much longer following a meal. So, basically these four snakes possess two different types of toxins in different places in their bodies, which come from different sources, and serve different purposes.

The "Venomous AND Poisonous Animal" photo below illustrates an example from one of the species of Garter Snakes (Thamnophis sirtalis) known to be poisonous (tetrodotoxin) and venomous (although Garter Snake venom is not dangerous to humans), while also pointing out where the poison glands (containing bufotoxins/bufadienolides) of the Garter Snake cousin, the Tiger Keelback Snake, are located (on the dorsum of the neck, behind the head).

So, if anyone ever asks you how many of the ~3150 species of snakes in the world are poisonous, you can give them an answer of at least four species (Thamnophis sirtalis/couchii/atratus and Rhabdophis tigrinus), with the caveat that they are both poisonous and venomous. Aside from those species, the remaining snakes in the world are either nonvenomous/nonpoisonous or venomous, with constrictors belonging to either of those categories.

The >1,300 species of venomous snakes may be further categorized into front-fanged (~600 species, ref #2) or rear-fanged (~700 species, ref #3) species and are introduced in the next hub on snake fangs, which you may feel free to explore after taking the quiz below to test your knowledge about how to distinguish venoms and poisons. You can also check out the video below, which shows how a nonpoisonous/nonvenomous constrictor kills prey. If you would like to learn more about venomous and/or poisonous creatures, please see the Amazon links throughout this article for some useful book resources. If you have further questions about snakes that are not addressed by this article on which snakes are venomous or poisonous (or any other articles in this Snake Venom hub series), please see my hub on FAQs About Snakes.

Venomous AND Poisonous Animal

An Eastern Garter Snake (Thamnophis sirtalis sirtalis), illustrating the Duvernoy's (venom) gland, the location of the rear-fangs (size is exaggerated), and the poison (nuchal) gland on the back of the neck in its cousin, the Tiger Keelback Snake

An Eastern Garter Snake (Thamnophis sirtalis sirtalis), illustrating the Duvernoy's (venom) gland, the location of the rear-fangs (size is exaggerated), and the poison (nuchal) gland on the back of the neck in its cousin, the Tiger Keelback Snake

Venoms vs Poisons

For each question, choose the best answer. The answer key is below.

  1. Venoms are most often what?
    • Created by the animal, itself, in specialized glands.
    • Sequestered from prey and stored in the skin and body tissues of the animal, itself.
  2. Generally speaking, can venomous animals be safely consumed?
    • Yes
    • No
  3. What is required for an animal to be venomous?
    • Fangs or stingers in order to introduce toxins into the flesh of its prey.
    • The ability to store toxins in its skin in order to ward off potential predators.
  4. Venoms primarily evolved as a chemical means of dealing with what?
    • Predators
    • Prey
  5. What are most Rattlesnakes considered?
    • Poisonous
    • Venomous
    • Both poisonous and venomous
    • None of the above
  6. How many species (roughly) of poisonous snakes are there in the world?
    • 0 species, because you can safely eat any snake species.
    • 4 species, but these snakes are venomous as well.
    • 1200 species, but some of these snakes are also constrictors.

Answer Key

  1. Created by the animal, itself, in specialized glands.
  2. Yes
  3. Fangs or stingers in order to introduce toxins into the flesh of its prey.
  4. Prey
  5. Venomous
  6. 4 species, but these snakes are venomous as well.

Nonvenomous/Nonpoisonous Snake (Ball Python) Grabbing Small Rat to Kill it via Constriction

References

  1. Nelsen, D.R., Nisani, Z., Cooper, A.M., Fox, G.A., Gren, E.C.K., Corbit, A.G., Hayes, W.K., 2014. Poisons, toxungens, and venoms: redefining and classifying toxic biological secretions and the organisms that employ them. Biol. Rev. Camb. Philos. Soc. 89 (2), 450-465.
  2. Vonk, F.J., Jackson, K., Doley, R., Madaras, F., Mirtschin, P.J., Vidal, N., 2011. Snake venom: From fieldwork to the clinic. Bioessays 33, 269-279.
  3. Weldon, C.L., Mackessy, S.P., 2010. Biological and proteomic analysis of venom from the Puerto Rican racer (Alsophis portoricensis: Dipsadidae). Toxicon 55, 558-569.
  4. Mackessy, S.P., 2010. The Field of Reptile Toxinology, in: Mackessy, S.P. (Ed.), Handbook of Venoms and Toxins of Reptiles. CRC Press/Taylor & Francis Group, Boca Raton, FL, pp. 1-21.

Disclaimer

This hub is intended to educate people ranging from snake experts to laymen about the particulars of distinguishing poisons from venoms. This information contains generalizations and by no means encompasses all exceptions to the most common "rules" presented here. This information comes from my personal experience/knowledge as well as various primary (journal articles) and secondary (books) literature sources (and can be made available upon request). All pictures and videos, unless specifically noted otherwise, are my property and may not be used in any form, to any degree, without my express permission (please send email inquiries to christopher.j.rex@gmail.com).

I wholly believe feedback can be a useful tool for helping make the world a better place, so I welcome any (positive or negative) that you might feel compelled to offer. But, before actually leaving feedback, please consider the following two points: 1. Please mention in your positive comments what you thought was done well, and mention in your negative comments how the article can be altered to better suit your needs/expectations; 2. If you intend on criticizing "missing" information that you feel would be relevant to this hub, please be sure you read through all of the other hubs in this Snake Venom series first in order to see if your concerns are addressed elsewhere.

If you enjoyed this article and would like to find out how you can help support snake venom research examining the pharmaceutical potential of various snake venom compounds, please check out my profile. Thank you for reading!

© 2012 Christopher Rex

Comments

Christopher Rex (author) from Durham, NC on May 11, 2018:

That would make for an interesting research topic! Thanks for sharing!

Roger on July 17, 2016:

I was just reading about the Hemachatus haemachatus (Rinkhals, Ring-necked spitting cobra) and its diet, which consists mainly of toads. I could not find the species of toad, so don't know whether they are toxic or not. But apparently at least some of the toads of Mozambique are.

I was wondering if it could potentially be one of the few poisonous snakes.

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