They float around the room at random and charge at Isaac in a manner similar to Chargers. However, unlike Chargers, they are flying, and thus will pass over obstacles until they hit the opposite wall; they also charge at a much faster pace.
Kamikaze Leeches (Unofficial name) are black Leeches with an eye in place of their mouth. They can be found naturally in Sheol, and can replace regular Leeches in any floor.
Their behavior is identical to regular Leeches, but they explode upon death, or upon collision with Isaac. This explosion has a larger blast radius than regular Bombs.
A new variation was added in the Wrath of the Lamb DLC: the Holy Leech (Unofficial name). It looks exactly like a Kamikaze Leech, but is colored white instead of black. They can be found very commonly in the Cathedral and in any floor where regular Leeches or Kamikaze Leeches can spawn.
Like Kamikaze Leeches, they charge at Isaac and explode, but with an increased blast radius and an Eternal Fly circling them, which can block Isaac's tears.
- If a Leech charges at you while it's aligned with a door, it will go through it and off the screen, until it eventually reappears when its charge ends.