Leeches are a type of monster in 'The Mist' and appear in Season 1 Episode 5, 'The Waiting Room'
The leeches make their appearance in the final few minutes of the episode, Kevin races his brother Mike through the mist on a gurney just after his surgery.
Kevin slips over a puddle of blood causing Mike to fall off his gurney, Kevin tries to help him up and drag him however Leeches start falling from the ceiling, they are revealed to travel as a swarm as they circle the roof above them, they start dropping 1 by 1 onto Mike, squirming and entering his fresh wound. Mike's body eventually is covered in Leeches, he gets Kevin to shoot him to put him out of his misery
- Leeches from the mist tend to travel in swarms of hundreds rather than alone
- The Leeches seem similar to the swarms of Flying Leechs that Pennywise assumed as one of his forms he used to kill Patrick Hockstetter with in Stephen King's novel, It.
- It is assumed that The Leeches were attracted to that area of the hospital due to the amount of blood smeared over the floors and the area is occupied by mist