The image below is of a dead Small Tortoiseshell caterpillar with three tachinid puparia (cocoons). These three all emerged one at a time from this caterpillar as larvae (which are slimy white maggots), then formed these hard puparia. We have around 200 of these, none of which have hatched as yet.

All Tachinid Flies share the parasitoid habit, their larvae are parasites in other insects.