Researchers have identified olfactory receptors that enable ants to smell and recognize workers, males, and their queen
(PHYSorg.com Biology)

Queen ants spend most of their time having babies. To reign supreme in a colony, they exude a special scent, or pheromone, on the waxy surface of their body that suppresses ovary development in their sisters, rendering the latter reproductively inactive workers that find food, nurse the young and protect the colony.