Carrying an ant pupal cocoon, an Australian rattle ant (Polyrhachis queenslandica) toils near its leafy nest, oblivious to the Arhopala wildei caterpillar attached to the cocoon. These butterfly caterpillars only eat the eggs and larvae of this one species of rattle ant, a highly specialized feeding behavior.

An adult butterfly will lay its eggs directly on top of the nest of these ants, who immediately carry newly hatched caterpillars into the nest. Why? Because—like Maculinea alcon caterpillars—A. wildei caterpillars smell just like ant larvae. "These caterpillars really are wolves in sheep's clothing," says Australian butterfly expert Rod Eastwood. "They're pale, thin-skinned grubs that the ants could easily rip to pieces if not for their chemical camouflage."