Aposematism

Aposematism is the advertising by an animal, whether terrestrial or marine, to potential predators that it is not worth attacking or eating.^[1] This unprofitability may consist of any defenses that make the prey difficult to kill and eat, such as toxicity, venom, foul taste or smell, sharp spines, or aggressive nature. These advertising signals may take the form of conspicuous coloration, sounds, odours,^[2] or other perceivable characteristics. Aposematic signals are beneficial for both predator and prey, because both avoid potential harm.

The term was coined in 1877 by Edward Bagnall Poulton^[3][4] for Alfred Russel Wallace's concept of warning coloration.^[5] Aposematism is exploited in Müllerian mimicry, wherein species with strong defences evolve to resemble one another. By mimicking similarly coloured species the warning signal to predators is shared, causing the predators to learn more quickly at less cost.

A genuine aposematic signal that a species actually possesses chemical or physical defences is not the only way to deter predators. In Batesian mimicry, a mimicking species resembles an aposematic model closely enough to share the protection, while many species have bluffing deimatic displays that may startle a predator long enough to enable an otherwise undefended prey to escape.