A Black Fly can eventually transform into this more dangerous Pooter if left near a pile of poop too long in the Binding of Isaac: Rebirth (BOIR)

The Pooter is a type of Fly in The Binding of Isaac: Rebirth (TBOIR)

The Pooter cannot harm the player by contact, however it can still fire blood shots at the player

It fires a single blood shot when the player gets in its line of sight

A Black Fly can evolve into a Pooter if left too long near poop