Venomous or Poisonous? 

Okay, it used to be simple for us biology nerds to distinguish “poisonous” organisms from “venomous” organisms. In lectures, I always boil it down the basic distinction of “whom is biting/stinging whom?” In other words, if you put it in your mouth or on your skin, and you get sick, then you have encountered a poisonous creature. Simple examples include some mushrooms, plants and frogs. On the other hand, if the organism puts the toxic substance into you, then you have encountered a venomous creature. Simple examples include some snakes, jellyfish, ants, bees, and even plants like stinging nettles. Pretty simple, correct?! Not so fast there, my friends. A career-length body of work led by U.S. biologist Edmund D. Brodie, Jr., and often including his biologist son E. D. Brodie III, has been challenging our abilities to pigeonhole these phenomena.

In order of discovery, let’s start with the Asian crocodile newt. All newts are poisonous, based on toxic glands in the skin. Very, very few predators can survive attempts to eat a newt. But, when the crocodile newt feels threatened, it spreads its ribs, and those needle-tipped ribs line up perfectly with large poison glands on the skin, actually piercing the animal’s own skin, and thereby anointing the tip of the rib with a nasty toxin. Try to handle or bite this guy, and you will be injecting its poison into yourself. Venomous, or poisonous?

Every Zoo Docent and educator knows to teach our guests that, while some snakes are venomous, there are not poisonous snakes. Hmm … hold on a minute there. Let’s consider another oddball phenomenon, again from the Brodie Laboratory. Here again, we have a newt. Some, but not all, populations of the rough-skinned newt in our own U.S. Pacific Northwest produce a very deadly neurotoxin called Tetrodotoxin (read up on blowfish, and the Japanese fugu dining experience, and Caribbean zombie culture if you want to know more). This toxin is so deadly that, as with all newts, very few predators survive attempts to eat them. Enter the local populations of the common garter snake, who can eat these newts with no ill-effects, or sometimes mere temporary paralysis.

These particular snakes then proceed to store the newt’s toxins in their livers for many months afterwards. A predator who eats these snakes will be poisoned by them. Indeed, the snakes truly are poisonous. The interesting fact that these particular snakes also are brightly colored adds an extra “warning signal to potential predators” aspect to an already complicated story.

Recently, investigations by Dr. Brodie and a group of Brazilian colleagues found something that I never could have imagined. They found (terrifically!) venomous frogs. In a twist on the now-familiar story of the crocodile newt, these two species of casque-headed treefrogs have small, very sharp bony spines on their skulls, directly underneath clusters of toxic glands on their facial skin. Pick up one of these frogs, or try to eat it, and they will vigorously push their head against your skin to introduce a toxin more potent than the most venomous vipers in South America—the lance-headed vipers, including the terciopelo, or fer-de-lance.

From: Jared, C. et al., 2015. Venomous frogs use heads as weapons. Current Biology 25:2166–2170. The paper is available as a free download from journal here: http://www.cell.com/current-biology/abstract/S0960-9822(15)00788-5

I have spent years of my life exploring remote areas and encountering unfamiliar creatures, great and small. One lesson I have learned the hard way, but thankfully not the fatal way, is the simple advice: “If you don’t know what it is, don’t touch it. And, whatever you do, don’t put it in your mouth.”

It is a wild world out there, my friends.
Joe Mendelson, PhD
Director of Research