TED-Ed Video Lesson Transcript:
One fine day, when Charles Darwin was still a student at Cambridge, the budding naturalist tore some old bark off a tree and found two rare beetles underneath. He’d just taken one beetle in each hand when he spotted a third beetle.
Stashing one of the insects in his mouth for safekeeping, he reached for the new specimen – when a sudden spray of hot, bitter fluid scalded his tongue.
Darwin’s assailant was the bombardier beetle. It’s one of thousands of animal species, like frogs, jellyfish, salamanders, and snakes, that use toxic chemicals to defend themselves – in this case, by spewing poisonous liquid from glands in its abdomen.
But why doesn’t this caustic substance, ejected at 100 degrees Celsius, hurt the beetle itself?
In fact, how do any toxic animals survive their own secretions? The answer is that they use one of two basic strategies: securely storing these compounds or evolving resistance to them.
Bombardier beetles use the first approach. They store ingredients for their poison in two separate chambers.
When they’re threatened, the valve between the chambers opens and the substances combine in a violent chemical reaction that sends a corrosive spray shooting out of the glands, passing through a hardened chamber that protects the beetle’s internal tissues.
Similarly, jellyfish package their venom safely in harpoon-like structures called nematocysts. And venomous snakes store their flesh-eating, blood-clotting compounds in specialized compartments that only have one exit: through the fangs and into their prey or predator.
Snakes also employ the second strategy: built-in biochemical resistance.
Rattlesnakes and other types of vipers manufacture special proteins that bind and inactivate venom components in the blood.
Meanwhile, poison dart frogs have also evolved resistance to their own toxins, but through a different mechanism.
These tiny animals defend themselves using hundreds of bitter-tasting compounds called alkaloids that they accumulate from consuming small arthropods like mites and ants.
One of their most potent alkaloids is the chemical epibatidine, which binds to the same receptors in the brain as nicotine but is at least 10 times stronger.