Wyrms

The most powerful of the Lesser Dragons, the wyrms were spawned in the Crucible of Purifying Flame, but the stuff of their genesis was not the purified fire which made up the Fire Dragons. Instead, the wyrms were created from the dross, leaving them subject to extreme, destructive rages. They are extremely large - the oldest of them longer and heavier than any Dragon - with serpentine bodies, thick, muscular necks and short, vestigial, or entirely absent limbs. They burrow using their vast, grinding jaws, consuming stone and earth in a digestive system akin to a perpetual firestorm.
  Wyrms are blessedly rare, of animal intelligence, and almost unstoppable. There is no known maximum size for these creatures, but the largest well-recorded specimens measured over three hundred feet long. Even younger wyrms, between twenty and fifty feet have formidable natural armour and the ability to generate some of the most terrible natural venoms known.
  Wyrm mating is rare and incredibly violent, leaving vast areas of devastation where the ground is riddled with leathery eggs about the size of a hen's egg. These hatch in about a hundred days, and while each individual wyrmling is the size of a grass snake, their voracious appetite and competitive drive transforms the already ravaged ground into a roiling mass of wyrmsand, a thin layer of stable soil covering a vortex of small tunnels and moving bodies which can collapse beneath an animal's weight, trapping them in a biting, smothering pit. Within a year of consumption - during which the primary source of nourishment is weaker wyrmlings - only a handful of python-sized specimens remain, and will scatter to find their own hunting grounds.
  There are orders of hunters, scholars and arcanists whose sole mission is to track individual wyrms and prevent or mitigate the impact of their attacks on populated areas, to respond to mating events and scour the area for eggs, and to kill as many wyrmlings as possible before they reach scattering size.