hehe
My daughter will go outside to play with the worms. Every so often she catches one and wants to keep it as a pet. She puts it in a bowl or glass and piles a bunch of greenery into it for food.
After a while she forgets about "Wormy" (her name for every one she tries to keep as a pet) and I let it go outside. When she remembers I just tell her womry went home to its mum and dad which satisfies her.