The difference between venomous snakes and poisonous snakes

Q: Are there poisonous snakes too? What is the difference between venomous snakes and poisonous snakes?

Krishna: According to biologists, the term venomous is applied to organisms that bite (or sting) to inject their toxins, whereas the term poisonous applies to organisms that unload toxins when you eat them. This means that very few snakes are truly poisonous. The vast majority of snake toxins are transferred by bite. One exception is the garter snake (Thamnophis), which is small and harmless in terms of its bite but is toxic to eat because its body absorbs and stores the toxins of its prey (newts and salamanders).

Common Garter Snake (Thamnophis sirtalis) 

Poisonous animals include most amphibians (that is, frogs, toads, salamanders, etc.), which carry around some amount of toxins on their skin and within their other tissues, such as the highly toxic poison secreted by various poison dart frogs. These chemicals are strong enough that they can be deadly to humans. So you shouldn't eat them. 

Along with snakes, dangerous spiders are also generally venomous. Some lizards are venomous as well; the potency of lizard venom ranges from relatively mild, such as that of the Gila monster (Heloderma suspectum) and various species of iguana, to the witches’ brew of toxins and bacteria injected into the prey of the Komodo dragon (Varanus komodoensis).

In addition, other animals (such as bees, ants, and wasps) are venomous even though they do not contain fangs per se. The platypus (Ornithorhynchus anatinus) is probably the best-known venomous mammal. Male platypuses have a fanglike spur on the inner side of each ankle that is connected to a venom gland located over the thighs. The spurs can be wielded in defense, and the venom is potent enough to kill small animals and to cause intense pain in humans if the spur penetrates the skin.

Similarly, cnidarians (jellyfish, corals, and sea anemones) have capsules called nematocysts (which may be tiny, elongated, or spherical) that contain coiled, hollow, usually barbed threads, which can be turned outward to ward off enemies or capture prey. These barbed threads often contain toxins.

Venomous snakes inject venom into their prey or predators using specialized teeth or fangs. The venom is designed to subdue or kill the prey and may also be used in self-defense. Venom is a type of toxin that is specifically adapted for injection.

Poisonous snakes, on the other hand, secrete or store toxins in their skin or flesh. These toxins are not injected through bites or stings, but rather must be ingested or absorbed through contact with the skin. Poisonous snakes are often brightly colored or have distinctive patterns to warn potential predators that they are dangerous.

Both venom and poison are toxins, which means they can cause harm to our bodies. The difference between venom and poison is how the toxin gets into a body. Poison is either eaten or touched, like poison ivy or arsenic. Those can only hurt you if you put them in your mouth or on your skin. Venom, on the other hand, is injected.

Some snakes can be both venomous and poisonous (1). There are a few species of snake that are actually poisonous. Rhabdophis keelback snakes are both venomous and poisonous – their poisons are stored in nuchal glands and are acquired by sequestering toxins from poisonous toads the snakes eat. Similarly, certain garter snakes from Oregon can retain toxins in their livers from ingesting rough-skinned newts.

Footnotes:

1. https://www.osc.org/can-snakes-be-venomous-and-poisonous/