Whers are misshapen creatures, created from fire-lizards, like Dragons. They were created by Wind Blossom Yung, the daughter of Kit Ping Yung, in an attempt to follow her grandmother's program, to add to the number of Dragons. Her attempt failed. However, the creatures that were produced proved to be Impressionable, like the Dragons, and, while photophobic, to have terrific night-vision, as well as a sensitivity to dangerous gasses. They thus proved useful as night guards and as aids to miners.
It was revealed in Dragonsblood, however, that the whers have an extra purpose. They fight Thread at night. They are tougher, in some ways, and more independant than the dragons. As a last resort, a possibility existed to transform whers into dragons.