A leech/maggot-like insect with pointy teeth.
One to three Blue Flies randomly spawn every time Isaac takes damage.
Regardless of how many Flies are spawned, no more than five will follow Isaac into the next room.
- Chemical Peel - The attack flies spawned by this item will deal increased damage if the last shot fired was a Chemical Peel shot.
- Sometimes a fly will attract to a non-enemy entity such as a chest when a troll bomb from the chest damages the player.