It is described as being a bulbous, dark creature, with many appendages such as spikes, shears, and rods. It seems to move in a forward roll. A Griever can "sting" Gladers, or prick them, which causes extreme pain for up to days or weeks. Stung Gladers who take the Grief Serum usually regain some of their memories during the painful "Changing." If a Glader does not take the serum, they die.
Grievers make whirring and clicking sounds when they move. The machinery inside of them often causes the reflectance of light, as described by Thomas. Grievers have stung four major characters in The Maze Runner: Ben, Alby, Thomas, and Gally.
Grievers appear to be easily tricked, as seen when Thomas and Minho tricked the Grievers into going over the Cliff. It is unknown if the Grievers actually intended to go into the Griever Hole. They are assumed to "charge" in oblong cell-like cages seen in WICKED headquarters and at the end of The Scorch Trials.
The Grievers in the film resemble gigantic spiders. Their sting causes symptoms like being uncontrollably aggressive, dark veins being visible. It does not become clear whether it also brings back some fragments of memory. In the Film Ben was stung by a Griever and subsequently goes through the Changing. Unlike in the book this means the symptoms of a Griever sting, not the Serum, like being uncontrollably aggressive, small bits of memory coming back. Grief Serum is unknown, though Teresa finds two syringes with unknown content in her pocket. Used on Alby after him being stung by a Griever it apparently calms him, maybe heals him.