Seed Eater

Seed Eaters are a species of monsters that prey and feed on children, they also are able to corrupt people who hear their sounds and whispers to do their biding. The children they eat either die or end up turning into a Seed Eater themselves, which is how they multiply. The Seed Eaters first came into the spotlight once they started to stalk Willow, a little girl from Georgia. Willow's sister Dana then proceeded to contact Stan for help. It's also later revealed that the Seed Eaters had stalked Travis' little brother too, and had succeeded in taking him.

2015
Durin the dark days, one of the Seed Eaters began prying on Nick, Travis' brother. The Seed Eater was able to capture Nick, never to be seen again. Travis then dedicated the rest of his time to finding information about the Seed Eater and to hopefully find his brother.

2017
Two Seed Eaters began to stalk Willow, a little girl from Maine. Willow's sister Dana then contacted Stan, as he was a paranormal investigator. Stan became very involved in their lives, even babysitting Willow at times because Dana had work. Stan had previous knowledge about the Seed Eaters, knowing that they transform children into their own kind. While babysitting Willow one day, Stan was attacked by the two Seed Eaters, trapping them in the garage but getting hurt in the process. Later on Stan met up with Travis in New York, who told Stan that the Seed Eaters can manipulate people, something Stan didn't know. Stan rushed to go to Georgia, as the Seed Eaters were still trapped in Dana and Willow's garage, fearing that they may have manipulated Dana. Stan called Willow, who told Stan that Dana had started acting weird and was getting ready to open the garage door. Dana then suceeded in opening the garage door, allowing the Seed Eaters to attack and eat Willow. This event caused Stan to fall in a deep depression, and became something that often haunted him.

2018 - 2020
The Seed Eaters returned in a nightmare Stan was having. Standing tall in the corner of a room. At a later point, Stan travelled in time and space to Dana and Willow's house. Dana was implied to have died, but Stan was able to find Willow in her room, having been turned into a Seed Eater after she was attacked and seemingly killed in 2017. Stan and Willow recognized each other and reconciled, before Stan put her out of her misery.

Trivia

 * The Seed Eaters were played by Evan Santiago.
 * The Seed Eater in the dream sequence of season 3 is supposed to be an amalgamation of a Seed Eater and the Man in the Suit, which is why the Seed Eater was so tall.