Pheromonal communication elicits physiologic and behavioural changes in the subject affected.
Pheromones were initially studied in insects, where they have an established role as proven by scientific research. Limited sensory development in insects as compared to mammals necessitates the presence of some communication mechanism by which they can exchange information. Pheromones are the substances which perform this function. The complex manner in which ants, termites, honey bees, bugs and other insects organise their daily life without any verbal communication is a definite clue to the presence of pheromones. All insects have a highly organised pattern of social interaction as well as a well defined reproductive pattern which are guided by pheromones.
According to an online article by Pines Maya of the Howard Hughes Medical Institute, the first pheromone ever to be identified (in 1956) was a powerful sex attractant for silkworm moths. It was isolated over a span of twenty years by a team of German researchers. After removing certain glands at the tip of the abdomen of 500,000 female moths, they extracted the compound. Miniscule amounts of this compound elicited excitement in the male moths exhibited by fluttering of their wings. This clear sign that the males had sensed the attractant enabled the scientists to purify the pheromone. The compound was purified subsequently and was named "bombykol" for the silkworm moth, Bombyx mori from which it was extracted.
There are enough visibly apparent instances of evidence of the existence of pheromones in our daily life when we observe insect behaviour. Bees and wasps home in to the precise location of their hives; ants leave a trail for others to follow, and the butterflies locate members of the opposite sex during flight.
Pheromones are predominantly volatile compounds detected by the sense of smell but sometimes can be liquid contact chemicals (Gullan P.J. et al). They are secreted from the exocrine glands derived from the epidermal cells. Classification of pheromones in insects is based upon five categories of behaviour associated with sex, aggregation, spacing, trail forming and alarm. Sex pheromones are usually secreted during the breeding season by the female which attracts the males. Aggregation pheromones cause insects of both sexes to crowd around the source of the pheromone. Spacing pheromones are anti aggregation and are secreted to repel further arrivals of the species when a particular spot is saturated with the species or the food source is exhausted. Trail marking pheromones are volatile and short lived chemicals that evaporate within days unless reinforced. They are used by social insects like ants to mark the trail to the nest or food source. Alarm pheromones are volatile, non persistent compounds that are secreted by insects during aggression by a predator or any other calamity which may affect the nest. They induce protection behaviour by collection or aggregation of the affected species such as bees.
The presence and significance of pheromones in higher species in the ecological order has been well documented but the role played by them in human beings has been full of claims, counterclaims and controversies. Social as well as sexual behaviour in the quadruped mammals is strongly influenced by the sense of smell. Territory marking is a prominent feature in animals like lions, tigers and dogs. Such animals can detect the presence of another male by the