Evolution has churned out some pretty exceptional defense mechanisms in the history of the natural world, from poop-hoarding bees to the craven “playing possum” response of Virginia opossums, but a worthy contender for the most grisly strategy has to be the assassin bug, Acanthaspis petax, which uses its victims’ corpses as a means of camouflage.
The assassin bug gets its sinister nickname for its lethal hunting technique. It uses its long proboscis to pierce its prey, often ants, and inject saliva laced with a paralyzing agent and enzymes, which dissolve tissue. The assassin bug then sucks up the contents of its prey until all that remains is a hollow exoskeleton.
Not one to waste a perfectly good corpse, it then fashions the bodies into a sort of morbid backpack. Assassin bugs can be seen walking around with as many as 20 dead ants glued to their back. The accessory corpses are bundled together in a lump sometimes larger than the living bug itself, which secretes viscous saliva to stick them together.
The purpose of this macabre practice was a subject of debate among scientists for many years. There were several theories as to how the ant-pack could be an effective means of defense, as either a visual or olfactory disguise from predators.
It wasn’t until a study in 2007 carried out an experiment to test the efficacy of corpse-carrying that it was established that the ants acted as a mask to obscure the assassin bug’s body shape, which drew the eye of predatory jumping spiders. Jumping spiders rely on their excellent sight to hunt, and when “naked” and “masked” assassin bugs were presented to them they attacked those without corpses 10 times more often than those with.
So now we know why they wear dead bodies, why ants? Why not adorn yourself with the corpses of all your victims? It's possible that by using ants, the assassin bugs benefit from jumping spiders’ innate aversion to ants as they make for tricky targets. If, unlike the assassin bug, you aren’t armed with paralyzing agents, ants under attack can fight back or swarm, which is bad news for a modestly sized spider.
Assassin bugs aren't alone in their passion for dead animal fashion. The mad hatterpillar will turn the empty sheddings of its own head into an impressive fascinator. It can shed its head up to 13 times and will begin stacking the remains from molt number four, so the stack can be up to nine heads tall. The bizarre behavior is employed for the same reasons as the assassin bug's corpse-carrying as it protects the caterpillar from aerial attack by bats. By bumping up the headcount it increases its chances of making it to shelter before a bat grabs its real head and the jig is up.