If you want to drive someone away, then throwing up on them is probably going to do the trick. But the caterpillars of the small mottled willow moth (aka the beet armyworm; Spodoptera exigua) take defensive vomiting to a whole new level. Their puke is both detergent and chemical weapon; its goal is not to cause revulsion but to break through the waterproof layer that its predators find so essential.

Willow moths are attacked by a variety of predatory ants. To study their defences, Rostas and Blassmann reared several caterpillars and exposed them to the European fire ant (Myrmica rubra). After mere seconds, the ants would attempt to bite and sting the caterpillar, which, in response, would regurgitate droplets