Crawlers

"Crawlers" are a human subspecies that adapted perfectly to their cave environment. Director Neil Marshall described them as "Cavemen that never left the caves". The two films in the series have shown their culture in a lot of detail, with many caverns and chambers having a specific purpose, such as feeding, drinking and defecating. Male and females have been shown as well, with females having a large amount of head hair, whilst males have none at all. Like some species of microbats, they are blind, but use sound to hunt. This can be used to the Human's advantage, as the crawlers can be distracted by noise-emitting objects, such as a bleeping watch or a "walkie-talkie" radio, allowing that person to escape. In the series, it is implied they hunt above ground, shown by the dead Deer, Elk, Hog, Goat and other carcasses in Part 1, and Crawlers dragging dead animals into the caves at the end of part 2. However, considering Ed dragged Rios to the cave entrance in Part 2, it is quite plausible that he hunts for them and leaves the prey at the cave entrance.