Grungs live in trees and prefer shade. A grung hatchery is maintained in well-guarded ground-level pools. About three months after hatching, a grung tadpole takes on the shape of an adult. It takes another six to nine months for a grung juvenile to reach maturity.

Green grungs are the tribe's warriors, hunters, and laborers, and blue grungs work as artisans and in other domestic roles. Supervising and guiding both groups are the purple grungs, which serve as administrators and commanders. (Use the grung stat block to represent members of the green, blue, and purple castes.)

Red grungs are the tribe's scholars and magic users. They are superior to purple, blue, and green grungs and given proper respect even by grungs of higher status. (Use the grung wildling stat block to represent members of the red caste.)

Higher castes include orange grungs, which are elite warriors that have authority over all lesser grungs, and gold grungs, which hold the highest leadership positions. A tribe's sovereign is always a gold grung. (Use the grung elite warrior stat block to represent members of the orange and gold castes.)

A grung normally remains in its caste for life. On rare occasions, an individual that distinguishes itself with great deeds can earn an invitation to join a higher caste. Through a combination of herbal tonics and ritual magic, an elevated grung changes color and is inducted into its new caste in the same way that a juvenile of the caste would be. From then on, the grung and its progeny are members of the higher caste.