pheromone

right|thumb|A fanning honeybee exposes [[Nasonov's gland (white – at tip of abdomen) releasing pheromone to entice swarm into an empty hive]]

A pheromone () is a chemical that is secreted or excreted by an organism, which triggers a social response in members of the same species. There are alarm pheromones, food trail pheromones, sex pheromones, and many others that affect behavior or physiology. Pheromones are used by many organisms, from basic unicellular prokaryotes to complex multicellular eukaryotes. Their use among insects has been particularly well documented. In addition, some vertebrates, plants and ciliates communicate by using pheromones. The ecological functions and evolution of pheromones are a major topic of research in the field of chemical ecology.