"Inside the caterpillar host, a cruel
drama takes place: the eggs of the parasitoid hatch and the larvae
feed on the body fluids of the host. The caterpillar continues
feeding, moving and growing like its unparasitized brothers and
sisters. When the parasitoid larvae are full-grown, they emerge
together through the host's skin, and start pupating nearby. Unlike
many other combinations of host and parasitoid, the host remains
alive but displays spectacular changes in its behaviour: it stops
feeding and remains close to the parasitoid pupae. Moreover, it
defends the parasitoid pupae against approaching predators with
violent head-swings."
link
