Social regulation of a rudimentary organ generates complex worker-caste systems in ants.

The origin of complex worker-caste systems in ants perplexed Darwin and has remained an enduring problem for evolutionary and developmental biology. Ants originated approximately 150 million years ago, and produce colonies with winged queen and male castes as well as a wingless worker caste. In the hyperdiverse genus Pheidole, the wingless worker caste has evolved into two morphologically distinct subcastes-small-headed minor workers and large-headed soldiers.