Humans frequently form short-lived cooperative groups to accomplish subsistence and economic tasks. We explore the ecological and cultural factors behind ephemeral work-group formation in two disparate cultural contexts: groups foraging for wild honey in present day South India and groups prospecting for silver ore in the Elk Mountain Mining District of Colorado in the late 19th century. Contrary to traditional economic foraging predictions, we find little evidence that per capita yields are the most important factor in determining size and composition of ephemeral work groups. We explore factors in each of these cultures that may be of importance for group formation such as kinship, reputation, and pleasure. Models that only incorporate economic parameters will make poor predictions of how humans interact with their environments.