Rough-skinned newts (Taricha granulosa) are kind of ugly and hella poisonous.
They produce tetrodotoxin, which makes it a really tragically bad idea to eat them. Unless you’re a garter snake, anyway. Garter snakes are currently locked in an arms race with them where the newts get more and more poisonous, and the snakes get more and more resistant to it, and eventually we’re going to have snakes that you just can’t poison and newts that can take their poison and shoot a concentrated beam straight out of their eyes.
And they do, as far as we can tell, produce it. It’s not like with poison dart frogs where they get it from something they eat, and frogs raised in captivity aren’t toxic. The newts remain poisonous as hell no matter how long you keep them in an aquarium, and at least one study has demonstrated that a well-kept rough-skinned newt will get more poisonous over time rather than less. That’s just how they roll.
Females pass the tetrodotoxin along to their egg clutches, which keeps most things from eating them. It actually attracts certain predators, like caddisflies, though.
Above: Those dicks.
They eat the eggs and sequester the toxin for use in their own defenses in a maneuver not unlike caterpillars loading up on alkaloids intended to keep herbivores off of the plants that produce them in order to keep predators off the caterpillars instead. Also (we think) not unlike the fucking garter snakes that feed on them.
No, for real.
Basically, when a garter snake’s liver is dealing with the tetrodotoxin it’s ingested, it winds up with this effective half-life of like eight days in the snake’s system. So it takes two months for the poison from one newt to fully metabolize out of the snake’s body. The poison functions in most animals by jacking up the sodium channels in cells. In garter snakes with a particular mutation, there’s no receptors for the poison to sneak in and bind to and fuck everything up. So they get a little fucked up on the poison for a few hours, but after that it’s no real thing.
But while the poison hanging out in the snake’s system isn’t hurting the snake, it makes no promises if you stuff the snake in your face and attempt to digest it. And if the snake’s making a pretty steady living eating newts, it’s packing enough poison in its body that anything that tries to prey on it’s going to wind up sick as hell and quite possibly dead.
These guys basically fear nothing as a result. Their response to being threatened to is poison harder and do a little yoga lift.
Above: You thought I was fucking kidding, didn’t you?
That pose is called the unken reflex. It’s used primarily by animals that engage in some sort of crypsis most of the time but are in fact ready to fucking fight you if you mess with them and have some aposematic surprises to show off. Animals that are venomous, poisonous, or just generally possessed of some nasty defense mechanisms love this one.
So, certain snakes and certain flies will eat them. What about humans? Yes, humans will also eat them. We are, in fact, the only mammal that will voluntarily ingest these little bastards, almost always following the phrase “As the result of a drunken dare…”. And yes, for the record, one newt contains enough poison to off an adult male human. We know this because a fucking dude fucking ate one and then fucking died from it after going to the fucking hospital. (Another, earlier dude ate one and then barfed it up in a reasonable amount of time. He was fine after a lengthy and unpleasant bout of medical intervention.)
In conclusion: Do not make drunken bets involving eating these newts, Jesus Christ, what is wrong with you, they taste terrible and will kill you. Unless you’re a garter snake, in which case where did you even get that booze, snake? Does your mother know you’re drinking? You’re not driving anywhere after this, are you?