Alarm pheromones

Definition

A class of semiochemicals released by an organism upon injury, disturbance, or predation threat that elicits rapid defensive or escape responses in conspecifics. In social insects, these compounds often trigger coordinated colony-level reactions such as aggregation, dispersal, or aggressive retaliation.

Etymology

From 'alarm' (warning signal) + 'pheromone' (Greek pherein 'to carry' + hormon 'stimulating'), coined in the context of chemical ecology.

Example

When an aphid is attacked by a lady beetle, it releases alarm pheromones such as (E)-β-farnesene from its cornicles, causing nearby aphids to drop from the plant and escape; similarly, honey bee workers release isopentyl acetate from the sting apparatus when injured, prompting nestmates to sting in defense.

Synonyms

• warning pheromones
• distress pheromones

Related Terms

• pheromones
• semiochemicals
• trail pheromones
• sex pheromones
• aggregation pheromones
• defensive behavior
• kin recognition
• chemical ecology

Usage Notes

Distinguished from 'disturbance pheromones' (which indicate non-predatory disruption) and 'death pheromones' (necromones signaling corpse removal). The term implies active release rather than passive leakage; some authors reserve 'alarm pheromone' for social species and 'distress signal' for solitary organisms. Context matters: in ants, alarm pheromones often recruit attackers, while in aphids they prompt dispersal—opposite tactical outcomes from similar chemical logic.