What's the Difference: Venomous Vs. Poisonous

At the Forest Preserve District, one of the more common questions we get is whether a particular snake is poisonous or if there are any poisonous snakes in the area.

A northern water snake. (Photo by Chad Merda)

The question can be frustrating for two reasons. First, Will County is not home to any snakes that cause harm to humans. But no matter how hard we try to get that message out, people are still afraid that a snake they cross paths with will harm them. The other reason this question can be difficult is because technically there’s no such thing as a poisonous snake in the United States.


That's right. No snakes in the U.S. are poisonous. However, some snakes are venomous. (But again, none of the snakes in Will County are venomous.)


Animals can be either poisonous or venomous, although most are neither. And with the exception of a very few animals, virtually no animals are poisonous and venomous. The difference between poisonous and venomous has to do with how the animals administer their toxins.


Venomous animals inject their toxins into you, usually through a sting or a bite. Think about a wasp, a bee or a scorpion stinging you, or the bite of a snake or spider. In addition, some fish species have venomous spines.


In the case of poisonous animals, they usually secrete toxins through their skin. People can get sick when you eat the toxins, either directly or indirectly. Poisonous animals are problematic when they are ingested. For example, you could get sick if you handled a poison dart frog and then accidentally licked your hand or ate something you held in your hand after handling the frog without thoroughly washing in between.


Poisonous animals are more rare than venomous animals, but plants can be poisonous as well. For example, deathcap mushrooms got their name because eating them can be deadly. Even some plants we consume parts of regularly contain toxic elements that cannot be eaten. For instance, rhubarb stalks are safe to eat, but the leaf blades of the plant are poisonous.


Both poisonous and venomous animals use their toxins to protect themselves from danger. Poisonous frogs use their toxins to prevent themselves from being eaten by predators. Venomous animals also use their toxins defensively, but they must deliver them via a bite or sting or by scraping their spines against another animal.


Poisonous animals don't usually make their toxins themselves. Instead, they often get them from their environment. Take monarch caterpillars, which eat toxic milkweed plants. The toxins in these plants give the butterflies a bitter taste that many animals avoid.


Venomous animals usually make their toxins themselves. These animals typically bite or sting other creatures to deliver their toxins because they aren't as effective on the digestive system, so they need a more direct way to enter the body.


Most toxic animals are either poisonous or venomous, but not both. However, as with many things in nature, there are exceptions. Take the Asian tiger snake, which delivers its toxic venom with its bite but is also poisonous because it eats poisonous toads and can store the toxins in glands on their necks. Female Asian tiger snakes can also pass their poisons on to their offspring, so the young snakes are able to defend themselves from predators at birth.


Have no fear, though. The Asian tiger snake lives far from Will County — as its name suggests, it lives in Asia — so you don't have to worry about any snakes you come across locally causing you any harm.

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