Metamorphosis

This morning Charlie was still recognisable as a caterpillar - by this afternoon, he was sporting his new look, but if you look closely you can still see original markings., especially towards the bottom.

Now. here's the thing.  My mandarin tree is covered with wasp galls - which look exactly like Charlie.  So how has he managed to work out that he needs to look like a wasp gall to escape detection from predators?