No butterflies have truly parasitic life histories. However, contrary to the received wisdom that all caterpillars eat leaves, some species are predatory. Larvae of the large blue are collected by ants and taken back to the subterranean nest where the guests provide protein-rich secretions from ‘honey-glands’ on their backs. In return, the caterpillars gorge on grubs in the brood chamber.
Such behaviour might be termed nest parasitism. Calyptra is a Eurasian genus of moth, the adults of which puncture skin and drink mammalian blood, but this is more analogous to a mosquito than a flea. And sloths harbour moths in their dense fur, but these do not feed on their hosts, instead feeding on the dung produced when the sloths descend the trees to defecate. Parasitism occurs in many insect orders and has evolved independently each time. Given a few more hundreds of millions of years, things might yet change for butterflies.