Pheromones are chemicals used to communicate with members of the same species. First described in insects, pheromones are often used to attract mates but in social insects, such as ants and bees, pheromone use is much more sophisticated. For example, ants use pheromones to make foraging trails and the chemical and physical properties of the pheromone molecules provide ants with a remarkable level of control. Pheromones are not a separate class of compounds; indeed, many pheromones are familiar and commonplace compounds. It is the way these compounds are used that makes them pheromones, and that makes them of interest to biologists. (Contains 1 figure.)