As far as I can tell, whatever they turn into is completely randomized. It's like how a child doesn't know how tall they'll end up once they're an adult, except stupider. Considering they've got some form of immortality that reverts them to an egg once they're killed, you would think they would remember if they just follow the same metamorphosis every time, but that would be too convenient, wouldn't it?

Hey, let's see you do better after dying.

I'm already working on immortality myself, so I'll pass.