Turn into what?

Along the paths around one of the Straw's Bridge ponds, was a silken tent attached to the stinging nettles. From within the tent was spilling forth a large number of strange-looking grubs with spiky growths along their backs. They belong to the Caterpillar of the Peacock Butterfly (Inachis io).

Looking at these odd little creatures, it is difficult to think that, all being well, they will eventually turn into one of the most beautiful insects to grace the British skies. Seen here in a photo by Nick Woolley.