Chemical Communication and Pheromones

How animals send and receive chemical messages between individuals — marking territory, attracting mates, raising alarms, and organising whole societies through scent.

Definition

Chemical communication is the transfer of information between organisms by chemical signals, and pheromones are chemicals released by one individual that elicit a specific behavioural or physiological response in another individual of the same species, complementing the internal chemical regulation carried out by hormones.

Scope

This topic covers chemical communication between organisms: the definition and classes of pheromones and other semiochemicals, the production and detection of these signals, and the physiological and behavioural responses they evoke, including releaser effects on behaviour and primer effects on physiology. It treats the role of chemical signalling in reproduction, social organisation, and defence across animals. Coverage is comparative and mechanistic.

Core questions

• What are pheromones, and how do they differ from hormones?
• How do animals produce and detect chemical signals?
• What kinds of responses do pheromones trigger?
• How does chemical communication organise reproduction and social life?

Key theories

The pheromone concept

Karlson and Lüscher defined pheromones as substances secreted to the outside by one individual and received by another of the same species, in which they release a specific reaction, distinguishing external chemical signals from internal hormones.

Releaser and primer effects

Pheromones act either as releasers, triggering an immediate behavioural response such as mating or alarm, or as primers, producing slower physiological changes such as altered reproductive state, broadening chemical communication beyond simple signalling.

Mechanisms

Animals synthesise signalling chemicals in specialised glands and release them into the air or water or deposit them on surfaces. Recipients detect these molecules with chemoreceptors — often dedicated olfactory or accessory olfactory systems such as the vomeronasal organ in many vertebrates or sensitive antennal receptors in insects — that are tuned to specific compounds, sometimes responding to extraordinarily low concentrations. The signal then evokes a response: releaser pheromones trigger immediate behaviour such as mate attraction, trail following, or alarm, while primer pheromones cause slower physiological changes, for example synchronising or suppressing reproduction or regulating caste in social insects. Because such signals coordinate behaviour and physiology among many individuals, chemical communication underlies mate finding, territory marking, parent–offspring recognition, defence, and the organisation of complex animal societies.

Clinical relevance

The study of chemical communication informs the control of pest and disease-vector insects through pheromone traps and disruption and contributes to the understanding of chemosensory physiology. This entry is educational reference material rather than medical guidance.

History

Butenandt's isolation of the silk moth sex attractant bombykol provided the first chemically identified pheromone, and Karlson and Lüscher introduced the term pheromone in 1959. Edward O. Wilson and others showed how chemical signals organise the behaviour of social insects, establishing chemical communication as a major mode of animal regulation.

Key figures

• Peter Karlson
• Martin Lüscher
• Adolf Butenandt
• Edward O. Wilson

Seminal works

• karlson1959
• hill2016
• randall2002

Frequently asked questions

How do pheromones differ from hormones?

Hormones are chemical messengers that act inside the body of one animal, whereas pheromones are released to the outside and act on another individual of the same species.

What is the difference between releaser and primer pheromones?

Releaser pheromones cause an immediate behavioural response, such as approaching a mate, while primer pheromones cause slower physiological changes, such as shifting an animal's reproductive state.