Crypsis & predator-prey relationship | Zoology Optional Notes for UPSC PDF Download

In nature predator and prey have evolved together for millions of years. Prey must deceive the predator in order to escape getting killed, while the predator must also use deception to catch the prey unawares. Crypsis is also a form of mimicry but the former has a wider meaning that includes mimicking even non-living objects such as stones, rocks, twigs and even the background.

Protective colouration: Majority of the animals match the background in colour to escape the attention of the predator. For example, hares and rabbits are earth-coloured, grasshoppers are green and beach crabs have the same colour as pebbles.

Counter-shading: This is also called natural shading, in which the protectively coloured animals have darker shade on the dorsal side and lighter on the ventral side of body. This is to neutralise the sunlight falling from above, which lightens the upper side of the body, while the shade below darkens the colour. Some animals press their bodies against the ground and remain motionless when in danger in order to eliminate the shadow. Flatfish, cuttlefish and chameleon can even change the body colour to neutralise the effect of light and shade. Squid (Abraliopsis) possesses light-producing organs on the ventral side, which can be switched on when there is sunlight from above and they become invisible from below.

Disruptive coloration: Another method to enhance the effect of natural shading is obliteration of the outline of body by having spots, patches or stripes, which break the continuity of the outline and thus help the animal to camouflage much more effectively. For example, salamanders, deers, leopards, tigers, fishes, rays all have patches on the body.

Protective resemblance: Some animals resemble their habitat not only in colour but also in structure, so that the camouflage is complete and they become completely inconspicuous in their environment. Caterpillars of the family Geometridae resemble the twig of the plant on which they feed in colour as well as shape. Similarly, sea horse possesses thread-like processes emanating from body, which make it invisible among seaweeds where it lives. Stick insects of the order Phasmida are found on grasses and have thin and elongated body and appendages, which make them look like strands of grasses.

Indian Leaf insect which feeds on broad-leaved plants in eastern Himalayas, has the entire body flattened and wings and legs shaped like leaves. The green, leaf-like insect is impossible to detect on green plants even by trained entomologists.

Aggressive resemblance: Predators also use crypsis so as to approach the prey undetected to mount a sudden attack. Many predators camouflage to ambush an unsuspecting prey that may wander near them. Tigers have stripes that help them to hide in tall grasses. Slow moving predators like praying mantis and ambush bug have the same colour and shape as the plant on which they sit and attack by surprise. Crab spiders are known to resemble flowers on which they wait for the prey, not only in colour but also in appearance.

The American hawk (Buteo albonotata) resembles vultures in general appearance. Since vultures are scavengers, birds are not scared of them and venture close to them, when the hawk in the garb of vultures attacks them.

Cryptic actions: Feigning death or injury is sometimes adopted as a measure to distract the attention of predator. Many beetles curl up like pebbles and remain motionless to escape attention of the predator. South American opossum also feigns death when alarmed. Echidnas, hedgehogs and porcupines also curl up when alarmed and feign death. Their body spines become erect as defence structures. Some birds, which make their nests on the ground, e.g. ostriches, lapwings and prancticoles feign injury on the wing or leg and struggle to run or fly to distract the attention of the predator from its nests.

Dymantism: Some butterflies, namely, pansies, colites and Melanitis, expose bright colours of wings when they suddenly fly, which temporarily frightens the predator and gives them time to escape. Some birds also expose flashes of bright plumage when they take to flight. Emperor moth is nocturnal and rests in shady places in daytime. Its wings possess large eyespots, which give a false impression of a hiding cat, which is enough for birds to avoid them. The butterfly, Nymphalis, has two pairs of eyespots on wings, which are revealed by lowering its wings when it is attacked by a predator.

Aposematism: Majority of protected species sport bright colours on the body to advertise their presence, so that the predators are warned not to attack them. The bright colours help in quick learning by the predators. For example, wasps that are protected by a sting are brightly coloured. Unpalatable butterflies, such as Danaus, are brightly coloured and are carefully avoided by the birds.

H.A. Ford demonstrated aposematism by conducting an experiment in which he used red and blue artificial caterpillars. Birds avoided the red ones.

Cryptic organs to misdirect attack: Swallowtail butterflies have long brightly coloured tail on the hind wing while the rest of the body is dull coloured. When the predators attack, they tend to catch the brightly coloured tail while the vital parts of the body escape damage. The small lantern butterfly (Thecla) has posterior extension of hind wing resembling head, while the actual head is small and inconspicuous. Bird attack is always misdirected on the false head.