Is a Snake Venomous or Poisonous? Venom vs Poison Explained

Venom vs poison: the simple rule

A quick way to remember the difference: if it bites you and you get sick, it is venomous; if you bite it and you get sick, it is poisonous. Both venom and poison are toxins, chemical substances that damage the body. The words describe the delivery route, not how strong the toxin is.

Venomous animals use toxins actively. Poisonous animals use them passively: the toxin protects them only after a predator has already grabbed or tasted them, and the warning is often bright coloration. See our list of the most poisonous animals for examples.

Why snakes are venomous

Venomous snakes make their toxins in venom glands on each side of the head, behind the eyes. The glands evolved from salivary glands, and muscles squeeze venom through ducts into the fangs, which inject it under the skin of prey. Elapids such as cobras and mambas have short, fixed front fangs; vipers have long, hinged ones; and many colubrids have grooved teeth at the back of the mouth.

Because the toxin must be injected to work, it counts as venom. Most snake venoms are mixtures of proteins, and proteins are largely broken down by digestion, so swallowing venom is generally far less dangerous than having it injected. That is one reason venomous snakes are usually not poisonous to eat. Learn more in how does snake venom work?

Why poison dart frogs are poisonous

The golden poison frog of Colombia is one of the most toxic animals known. Its skin contains batrachotoxin, a substance that keeps nerve and muscle cells from switching off. A wild frog is often estimated to carry enough toxin to kill several adult humans, though exact figures vary.

The frog has no fangs, spines or stings. It is poisonous because a predator that bites or swallows it, or touches the toxin to a wound or mucous membrane, absorbs the toxin. Its bright yellow color warns predators to stay away. Poison frogs get their toxins from their diet of small invertebrates, which is why frogs raised in captivity on other food are not toxic.

Exceptions: snakes that are also poisonous

A few snakes break the simple rule by being poisonous as well as, or instead of, venomous.

Tiger keelback. The tiger keelback (Rhabdophis tigrinus) of East Asia has two rows of special glands on the back of its neck. It fills them with toxic steroids called bufadienolides that it takes from the toads it eats. When threatened, it arches its neck toward the attacker, and if a predator bites the neck, the glands release the toxins. Females can even pass the stored toxins to their eggs. The tiger keelback also has rear fangs and a venomous bite, so it is both venomous and poisonous.

Garter snakes. Some common garter snakes in the Pacific Northwest eat rough-skinned newts, which contain tetrodotoxin, the same toxin found in pufferfish. Resistant garter snakes can store the toxin in their liver for weeks, which makes them poisonous to predators that eat them. Read more in how garter snakes eat toxic newts.

What about spitting cobras?

Spitting cobras of Africa and Asia can spray venom from their fangs toward the eyes of a threat, without biting. Strictly speaking, that venom is not injected through a wound. Some scientists have proposed a third term, toxungen, for toxins that are sprayed, spat or smeared onto another animal’s body surface. Spitting cobra venom fits this description, as does the formic acid that some ants spray. In everyday terms, spitting cobras are still called venomous snakes.

Why the difference matters

The words “venomous” and “poisonous” are often mixed up, and in casual speech “poisonous snake” is very common. For biologists the distinction matters because it reflects how an animal uses its toxins: venomous animals usually hunt with them, while poisonous animals use them to avoid being eaten.

It also matters for safety. A venomous snake is dangerous mainly because of its bite, so the best protection is to keep your distance and never handle a snake you cannot identify. Anyone bitten by a snake should seek emergency medical help immediately by calling 911 (US), 112 (EU) or 999 (UK). A poisonous frog or toad, on the other hand, is a risk mainly if it is handled roughly or put in the mouth, which is why wild amphibians are best admired without picking them up.