Final answer:
Grievers in 'The Maze Runner' are monstrous, semi-mechanical creatures that patrol the Maze and can deliver a dangerous sting.
Step-by-step explanation:
In the book "The Maze Runner," Grievers are terrifying, semi-mechanical creatures that roam the Maze during the night. They are described as large, amorphous, slug-like monsters with mechanical arms and various weapons. The Grievers are tasked with patrolling the Maze and can inflict a sting that causes extreme pain and disorientation, often leading to the changing of those who survive it. The fear that the Grievers instill in the Gladers is a significant part of the book's tension and is central to the Maze's function as a test for the characters.