But that’s not the whole story.
Some parasitic wasps are “hyperparasitoids”—they target other parasitoid wasps. And they also track the cabbage’s alarm chemicals, so they can find infected caterpillars. When they do, they lay their eggs on any wasp grubs or pupae that they find. Their young devour the young of the other would-be parasites, in a tiered stack of body-snatching. It’s like a cross between the films Alien andInception.
Erik Poelman from Wageningen University in the Netherlands studied one of these grisly networks: the caterpillars of the small cabbage white butterfly are attacked by two parasitoid wasps—Cotesia rubecula and Cotesia glomerata—which in turn are attacked by the hyperparasitoid Lysibia nana.
L.nana lays one egg in every wasp grub or pupa that it finds. C.rubecula produces a huge grub, but it only lays one in each caterpillar. C.glomerata is the better choice for a host—its smaller larvae offer less room for L.nana’s own progeny, but it implants around 20 to 40 of these into the same unfortunate caterpillar. If L.nana can find one of these clusters, it can parasitise an huge brood of wasp larvae in one visit. And it can find them thanks to the cabbage.