A pheromone (from Greek phero "to bear" + hormone from Greek – "impetus") is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual. There are alarm pheromones, food trail pheromones, sex pheromones, and many others that affect behavior or physiology. Their use among insects has been particularly well documented. In addition, some vertebrates and plants communicate by using pheromones. A notable example of pheromone usage to indicate sexual receptivity in insects can be seen in the female Dawsons burrowing bee, which uses a particular mixture of cuticular hydrocarbons to signal sexual receptivity to mating, and then another mixture to indicate sexual disinterest. These hydrocarbons, in association with other chemical signals produced in the Dufours gland, have been implicated in male repulsion signaling as well.
The term "pheromone" was introduced by Peter Karlson and Martin Lüscher in 1959, based on the Greek word pherein (to transport) and hormone (to stimulate). They are also sometimes classified as ecto-hormones. German Biochemist Adolf Butenandt characterized the first such chemical, Bombykol (a chemically well-characterized pheromone released by the female silkworm to attract mates).