a species, called "burrowers" by the natives, used to subsist on buffalo. when white settlers depleted the buffalo, the species began to survive on human meat - first hunting nearby indians and later the settlers. one tribe in particular, the ute, have experience in combating the hunter-species. the "burrowers" first lace their victims by cutting them and drugging them with a toxin. the victim is then buried alive and eaten only after decomposition has begun. by the time the film's protagonists meet up with the ute their numbers are severely depleted, but the ute method of drugging someone already infected with "burrower" toxin proves effective. when the "burrowers" go to eat the twice drugged victim they themselves fall asleep and are vulnerable, especially to the rays of the sun, which are the only apparent thing that can kill them. however, the surviving member of the posse, the irishman coffey, is unable to discover exactly what the ute used to drug the "burrowers", as most of the remaining ute are executed by the overzealous cavalry. the film ends with the suggestion that the "burrower" attacks will continue.