Which animal is immune to rattlesnake venom?

In 1976, a student at the Texas A&M University-Kingsville was tasked with feeding the snakes in what is now the university’s National Natural Toxins Research Center. Thinking it didn’t make much difference what kind of rodent the snake ate for dinner, the student offered one of the Center’s western diamondback rattlesnakes a fuzzy woodrat. The snake sunk its fangs into the rat’s fur—a maneuver that’s usually followed by near-instant hemorrhaging, clotting in the liver, and cardiac arrest. But nothing happened.

Woodrats weigh less than a pound, have neither large claws nor crazy fangs, and certainly don’t look capable of tangling with a full-grown rattlesnake. And yet, when the scientists repeated the trial, they found that the woodrats not only held their own against the rattlers, the rodents sometimes scratched and bit the snakes...to death. Woodrats, as it turns out, are immune to rattlesnake venom.

Some creatures have been found to have molecular defenses — whether it's a venom neutralizing peptide in their blood or actual cellular mutations that block venomous toxins — much like a wad of gum in a keyhole.

Not all critters need fancy molecular mechanism to defeat venomous creatures. Some creatures just evolved really, really thick skin. The honey badger has both: molecular defenses against cobra venom’s neurotoxins, and loose, thick skin to help it avoid getting struck in the first place.