#roughskinnednewt

“Our cruisers can’t repel firepower of that magnitude”

-        Admiral Gial Ackbar (saying something OTHER THAN “IT’S A TRAP,” PEOPLE. Please. Show some damn respect), Star Wars Episode VI: Return of the Jedi1

In 1979, a 29 year old dude was doing some day-drinking. As 29 year old dudes are wont to do, he followed that up by taking a poorly conceived dare from what I assume to be his friends (this was seven hours after the drinking had occurred, so presumably he had some time to sober up). The dare involved swallowing a 20 centimeter rough-skinned newt (Taricha granulosa). A few hours later he was dead. The cause was determined to be the newt, in isolation (as in, while he had been drinking earlier in the day and therefore had some toxins in his system, the amount of neurotoxin – specifically tetrodotoxin – found in the newt was sufficient to end a grown man)2.

This rough-skinned newt was not a particularly deadly rough-skinned newt. It was not the Boba Fett of rough-skinned newts, or something. It was a standard rough-skinned newt. Most newts do not live under the threat of predation by large primates, or really any large animal. They swim around and do their newt thing, and occasionally get snapped up by terrapins, turtles, fish, frogs, other newts, maybe the occasional bird…you get the picture. Small bodied animals. Things you don’t need enough poison to kill a human to defend yourself against. So why does the rough-skinned newt waste energy and evolutionary resources on firepower like that?

The same reason billionaire genius CEO Lex Luthor walks around with radioactive meteor bling that gives him cancer periodically: they have an archnemesis.

The garter snake Thamnophis sp. is a widespread but unassuming snake. It has a very mild level of venom itself – so mild that for quite a long time we believed it had none at all3. They’re extremely widespread, and not very big. Kids catch them in backyards, harass them for a while, and let them go. That kind of thing.

You don’t need to call in Rikki Tikki Tavi for these guys.

But to rough-skinned newts, garter snakes are ferocious predators. So ferocious that their entire toxin defense system has become “overbuilt” (in the same sense as those Pronghorn) to deter garter snakes, which, in turn, have an insane level of immunity to the particular brand of tetrodotoxin (most snakes are 200 times as resistant as mice to rough-skinned newt toxin; garters are 2000 times as resistant). Or at least, the ones that live in the same areas as rough-skinned newts do (in the business, we call that kind of habitat sharing “sympatry”)4. In fact, the level of toxicity of any given population of rough-skinned newts is a close match for the level of resistance to tetrodotoxin found in the local garters – if you mix and match from different populations, one side or the other gets an advantage4,5.

But Kaa don’t raise no fools. Garter snakes taste-test individual newts for toxicity. If they’re overmatched, this can be fatal, or at least result in severe paralysis and a very painful experience (snakes will bite their own throats during the poisoning. If the newt is too toxic, they let it go. If not, in the words of Audrey II, “It’s suppertime.”6   

“Star Wars Episode VI: Return of the Jedi” (1983)

Bradley SG, Klika LJ (1981). A Fatal Poisoning From the Oregon Rough- Skinned Newt (Taricha granulosa). Journal of the American Medical Association, 246:247

Vest DK (1981) The toxic Duvernoy’s secretion of the wandering garter snake, Thamnophis elegans vagrans. Toxicon, 19:831-839

Brodie ED III, Brodie ED Jr (1991) Evolutionary Response of Predators to Dangerous Prey: Reduction of Toxicity of Newts and Resistance of Garter Snakes in Island Populations.

Brodie ED Jr (1968) Investigations on the skin toxin of the adult rough-skinned newt, Taricha granulosa