Advantages of aposematism

Mechanisms for defence against predators takes many forms. A common adaptation is camouflage, where

Mechanisms for defence against predators takes many forms. A common adaptation is camouflage, where the animal avoids being eaten by its predator by merging with the background, by adapting specific colouration or shape. The leaf insect acquires the shape and colour of a leaf. It even sways as it walks, to resemble the swaying of a leaf in the breeze. The dead leaf butterfly (Kallima inachus), when its wings are folded, looks like a dried leaf.

Sometimes, animals pursue the very opposite tactic to avoid being eaten by predators. Instead of merging into the background, they actually aggressively advertise themselves through colouration or shape that they are not worth eating. The brightly coloured animal could be toxic, taste bad, smell foul or have spines or just be too aggressive. Perceiving that there is no profit in eating them the prey leaves them alone.

This tactic is called aposematism and the animal which pursues this is aposematic. The word aposematic is derived from the Greek (‘apo’ standing for ‘away’, and ‘sematic’ standing for ‘sign’).

Aposematism works best when members of the prey are located together in large numbers. A few members are eaten by the predator, who then realises that they are not worth eating and the rest are left alone. The most common colours are red, yellow, black and white.

There are many examples of aposematics. Among these, the ladybird and the tiger moth are bitter to eat. The poison dart frog has poisonous glands which can cause pain and the skunk has a foul-smelling odour.

There are also animals that are not really poisonous or obnoxious in any other way, but sport bright colours that can cheat the predator into believing they are not good to eat: For example, the hornet moth which looks like the yellowjacket wasp. The predator is fooled into thinking that the moth will sting it and so it leaves the moth alone.

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