A chemical substance or a blend of substances, usually a glandular secretion, which is used in communication within a species: One individual releases a pheromone as a signal and another responds after tasting or smelling it.

Primer pheromones alter the physiology of individuals and prepare them for new behavioral repertories. Releaser pheromones evoke responses directly.

A chemical substance exchanged among members of the same species that induces a state of alertness or alarm in the face of a common threat: Jeff read about thealarm pheromone referring to the release or ejection of a certain substance to alert the others of the same species of an oncoming danger, threat, or attack.