What snakes are venomous/poisonous?
Table of Contents for this Hub Series on Snake Venom
Venomous vs Poisonous Introduction/Summary Video
Common Characteristics of Poisons/Venoms
Toxin delivered by:
Toxin immunity, resistance
Can be safely injected?
Can be safely ingested?
Can absorb through skin?
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.
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
Venoms vs Poisonsview quiz statistics
Nonvenomous/Nonpoisonous Snake (Ball Python) Grabbing Small Rat to Kill it via Constriction
- 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.
- 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.
- 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.
- 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.
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 firstname.lastname@example.org).
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© 2012 Christopher Rex