Technical Abstract: Caste systems and the division of labor they make possible are common underlying features of all social insects. Multiple extrinsic factors have been shown to impact caste differentiation; for example, primer pheromones are chemical signaling molecules produced by certain castes that impact developmental physiology of nestmates. Thus, chemical signaling in social insect colonies is integral for maintaining caste homeostasis and a cohesive, efficient social structure. We examined the influences of terminally developed soldier termites (Reticulitermes flavipes) on (1) candidate primer pheromone levels and (2) caste differentiation in developmentally totipotent workers. Our findings provide evidence that the two main soldier terpenes, '-cadinene (CAD) and '-cadinenal (ALD), accumulate in nestmate workers only in the presence of soldiers, that soldiers can modulate developmental-hormone response thresholds of workers via CAD and ALD action, and that CAD and ALD (respectively) are caste stimulatory and inhibitory components of chemical blends present in soldier heads. Together these findings provided novel evidence that soldiers influence worker caste differentiation by either transferring terpene primer pheromonal compounds to workers, or by influencing de novo biosynthesis of these compounds in workers themselves.