The Skullcrawlers are the tertiary antagonists of Kong: Skull Island. They are monsters who lives in the Island and they are lead by Ramarak, alpha of their kind.
Kong: Skull Island
After the Sky Devils Team incident with Kong, Conrad and the survivors are in an old structure which is under the control of an ancient community. There they meet Marlow who tells them that it is not with whom one should fear but a few creatures called Skullcrawlers, monsters who responsible for the death of his partner and are looking to feed to square their neverending hunger.
Jack Chapman, who was one of Sky Devils' commandates, is killed by one of them while he was distracted.
When Conrad and Skydevils arrive, they encounter one of the Skullcrawlers who murder Randa and several members of Sky Devils. During the battle, it is revealed that this Skullcrawler is the one who killed Chapman, and two members of the survivors are in open area that made them easily spotted by predators of the island. Conrad runs to save his friends in an attempt to kill them, San with a lighter manages to kill it.
When Marlow explains the history of the island, he mentions how Kong battles with the skullcrawlers, leading into a flashback showing a short battle between Kong and multiple sub-adult skullcrawlers, these ones being fairly large, almost as big as Kong himself. Kong eventually kills the group of beasts, as Marlow reveals that Kong is believed to only be capable of handling these sub adults.