Defence against predators

's main defence against predators.]]
 contains the toxin *epibatidine*]]

For most animals, **defence against predators** is vital. Being eaten is not the only threat to life: parasites and diseases may also be fatal. But many animals are carnivores, and others, especially small animals, are often eaten. 

Since life is about reproduction, anything that keeps a creature alive long enough for it to reproduce will be selected for. The next generation comes from the fertilised eggs of the previous generation.

Not surprisingly, then, animals have developed a wide range of defences against predation. Some of these defences apply also to plants: herbivory on plants can be very damaging, and reduce a plant's fertility. Many plants have some defence against herbivores.

## Primary defences 
Primary defences make it less likely that there will be a meeting between the predator and the prey. In many cases this means the predator has not  or  the prey.

### Definitions 
There are various definitions of what a primary defence is:
*Robinson 1969: those defences which operate before a predator starts any prey-catching behaviour.
*Kruik 1972 and Edmunds 1974: defences which operate whether or not a predator is nearby.
The second kind of defence is very obvious. It is to carry armour and/or offensive weapons like horns. These are permanent visible defences. For larger prey animals this can be effective if linked to another defence. Thus, in natural habitats, elephants have tusks, and they also have huge size. Antelope have horns, and can also run fast. Almost all large herbivores live in herds, which undoubtedly is safer than living alone.

## Secondary defences 
. Seen from a distance  the stag is camouflaged, but able to fight or run fast. This is an alert posture, and a mild threat display. If the stag turns directly head on and lowers the head, that's a full threat display.]]
These work when a predator detects a prey, or when a prey notices a predator. The function of secondary defences is to increase the chance of the prey surviving the encounter (meeting).

### Methods 
'' shows startle display on its rear wings]]
's wing has suffered from a bird's beak, but the butterfly was still flying around]]
 butterfly with distraction 'targets' on its wings]]

*Withdraw to a prepared retreat: many methods. The pearl-fish *Carapus apis* retreats backwards into the anus, and then into the body cavity of a sea cucumber (*Holothuria*).p138 It turns out that the fish, when a juvenile, is a parasite on the sea cucumber. Although it is free-living as an adult, it is still able to re-enter the holothurian when danger threatens. Better-known examples include the tortoise, which just withdraws its head and legs under its shell, and the hermit crab, which retreats into its shell when in danger.
*Flee: run or fly away: a popular plan. Animals may flee in a straight line, or zig-zag. Another method is to fly showing some flash colour, and then suddenly settle completely still in camouflage. There are a number of moths with bright hind wings which are covered when at rest.
*: look threatening or startling (deimatic behaviour). The prey may adopt a posture which causes the predator to pause. This is sometimes called a 'startle display'. The predator may not know whether the display is  a genuine threat or a bluff. Either way, the prey has improved its chance of escape.
*Play dead (thanatosis): many vertebrate predators reject dead animals. Many predators strike to kill only on prey which move. That includes cats, lizards and mantids. A number of insects play dead when attacked. Some larger animals also do this, like the American Opossum. What playing dead does is avoid releasing the predator's inherited killing behaviour.
*Deflect or distract the attack. Many offer a non-essential part of the body, for example, butterflies whose wings have small 'targets' near the edges. Cuttlefish squirt out a cloud of black ink, turn  and swim fast away from the ink. The Kentish plover, which lays its eggs on the ground, lures attackers away from the eggs. It uses a remarkable impression of being damaged with a broken wing. When the predator is well away from the eggs, the bird flies off.]]

## Related pages 
*Defence against herbivory

## References 
## Other sources 
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