An effective communication co-ordinates these individuals and is generally induced by chemicals, although soldier termites sound an alarm by beating their large hard heads on the passage walls. Other chemical hormones (also called pheromones) in effect circulate instructions and dictate both actions and the development of the colony. All members of the colony exchange food and saliva with each other by way of the workers who also gather the excrement in order to reprocess it for food to obtain the maximum nutrition from it. The queen produces a pheromone, which is collected by workers and circulated through the colony. Although the queen termite produces both sexes, the queen's pheromones inhibit development maintaining them as sterile, wingless and blind (=workers). How soldier termites are produced is unknown (either specialized eggs or preferential treatment of larvae). Soldier termites have their own unique pheromone which is circulated through the colony and reaches the queen who probably regulates their numbers.