Hell on Earth: Gimme Shelter
They call these great worms “rattlers” because a person’s teeth start chattering as the rattler rumbles through the earth beneath him. Though they are most common in the Mojave (hence the name), rattlers are also found in isolated flatlands in Montana and Utah. The rattlers of each region tend to have their own colors and even personalities.
Mojave rattlers go straight for the kill, while the ones in Montana are skulkers. Utah rattlers are smaller but faster, and they absolutely love to chase steam wagons across the great Salt Flats. Like Maze dragons, rattlers are accepted near the regions they terrorize. Indeed, around Salt Lake City, there is even a trade in rattler skins and meat, leading to a growth industry in rattler hunting in the 1870s.
Rattlers can grow up to 100 yards in length, but the source of their sustenance has long been in dispute. They proliferate in areas in which there is little natural game for more conventionally-sized predators, let alone something the size of a fully grown rattler. Darius Hellstromme once posited that the rattlers draw sustenance from the earth through which they tunnel like their tiny annelid cousins, but that does not explain the apparent relish with which rattlers devour live prey when available, or why they are such efficient hunters.
Rattlers hunt by means of vibration sensitivity, tracking prey they detect walking or riding on the surface. When a rattler moves in for the kill, it bursts up through the earth and tries to snag its prey with one of its tentacles. Though they have many tentacles, they never attempt to capture multiple targets unless their intended victims are very close together, such as a horse and rider, preferring to focus on a single quarry.
Oddly, worms encountered in the wild fall into two groups: the massive adults and the comparatively tiny larval rattlers. Rattler larvae are found all over the Badlands. All juvenile rattlers ever observed or captured in the wild have been roughly three feet long. Young rattlers travel in packs of six or more. The prevalent theory is that the creatures stay underground until they reach this size, prowl around the surface for a while, then go down for further incubation. Due to the difficulty in finding evidence on other parts of the rattler lifecycle, there is no commonly accepted theory on rattler reproduction.
Since Judgment Day, there have been reports of mid-sized rattlers appearing in ruined cities. These so-called "urban worms" are between ten and twenty yards long and have a metallic, segmented carapace covering their body, which is a notable difference when compared to both the adult and juvenile rattlers previously observed. This physiological discrepancy has lead to some speculation that these urban worms may not actually be rattlers, but the otherwise overwhelming similarities leads many to believe this is simply a unique aspect of a middle phase of the rattler lifecycle.
Further muddying the waters with regard to unique species is the appearance of the Wormlings. Though there had been isolated (usually uncomfirmed) sightings of creatures matching the description of these bipedal worm-like beings prior to Judgment Day, they are now a common danger in the tunnels and ruins of the wastes. It is unknown how, or even if, the wormlings are related to the enormous rattlers.