Defensive display

Deimatic behaviour, threat display, or startle display in animals means any pattern of behaviour, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape. The term deimatic or dymantic originates from the Greek root δειματόω (deimatόo), meaning 'to frighten'.

Deimatic display occurs in widely separated groups of animals, including moths, butterflies, mantises and phasmids among the insects. In the cephalopods, different species of octopuses,squids, cuttlefish and the paper nautilus are deimatic.

Displays are classified as deimatic or aposematic by the responses of the animals that see them. Where predators are initially startled but learn to eat the displaying prey, the display is classed as deimatic, and the prey is bluffing; where they continue to avoid the prey after tasting it, the display is taken as aposematic, meaning the prey is genuinely distasteful. However, these categories are not entirely mutually exclusive. It is possible for a behaviour to be both deimatic and aposematic, if it both startles a predator and indicates the presence of antipredator adaptations.

Vertebrates including several species of frog put on warning displays; some of these species have poison glands. Among the mammals, deimatic displays are found in species with strong defences, such as in foul-smelling skunks and spiny porcupines. Such displays are often combined with warning coloration. Thus these displays in both frogs and mammals are at least in part aposematic.

Deimatic displays are made by insects including the praying mantises (Mantidae) and stick insects (Phasmatodea). While undisturbed, these insects are usually well camouflaged. When disturbed by a potential predator, they suddenly reveal their hind wings, which are brightly coloured. In mantises, the wing display is sometimes reinforced by showing brightly coloured front legs, and accompanied by a loud hissing sound created by stridulation. For example, the grasshopper Phymateus displays red and yellow areas on its hind wings; it is also aposematic, producing a distasteful secretion from its thorax. Similarly the threat display of the walking stick phasmid (Peruphasma schultei) is not a bluff: the insect sprays defensive dolichodial-like monoterpene chemical compounds at attackers.

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