In the insect world evolution likes to push the envelope, and the Bombardier beetle is no exception.
In fact, it's probably won 'Ma Natures most extreme badass award'.
Extreme emphasis on badass.
The Bombardier beetle doesn't have a backside, it has a reaction chamber. It's similar in design to what you'd find on a rocket: When threatened the beetle releases two chemicals, hydroquinones and hydrogen peroxide, into the reaction chamber. Where they produce a steam explosion.
A steam explosion in your abdomen doesn't sound like a great defence mechanism, but then the beetle opens a valve......
And the attacker finds out what a 'death fart' really is: