Mimicry can be classified into three categories:
1. Protective mimicry.
2. Aggressive mimicry.
3. Conscious mimicry.
1. Protective Mimicry
It is of highly specialized character and the organisms mimic themselves in the form, as well as in colour to protect the animals from enemies or predators. It is also responsible for camouflage of an animal by its close resemblance to its general background or to some dead or dull objects which is of no interest to its enemies. Protective mimicry has two aspects: (a) Concealing and (b) Warning
(a) Concealing mimicry
It is a very common amongst animals. In some cases the animals mimic the shape and colour of other organisms or object. In other cases the animals conceal themselves either by changing their colouration or search a background which matches with their colours. A number of examples can be quoted here.
A very typical example of the concealing or protective mimicry is given by the crab, Cryptolithodes whose smooth rounded form and texture and white colour very closely harmonize with the white pebbles of the beach and the true organic nature of the animal is apparent only when the animal, by accident, is turned over. The animal thus secures immunity from enemies of its own station.
The mimicry of the animal is of unconscious type, as action would clarify its presence and passivity is essential to safety. There are some other examples of crab which resemble wave-worn dead corals; in this case the animal is carnivorous and the concealment has two functions, protection against its enemies and aid in securing its prey.
The caterpillars of geometrid moths (Solenia tetraunaria) are not only protectively coloured but may mimic the twigs and smaller branches of various plants.
So perfect is the resemblance and so long maintained the posture that it is very difficult to detect. In the moth Schizura, both caterpillar and the adult show mimicry.
The most perfect examples of mimicty is the leaf insect known as Phy Ilium. It closely resembles a green leaf in colour, flattened wings, expanded body and limbs. Even the irregular small yellowish spots similar to the fungus growths upon leaf are also seen. Another noteworthy example is that of Kallima paralecta from India.
In this butterfly, hind wings are stem-like. The wings are strikingly coloured above, blue black with reddish, yellow or bluish spots with band but when it is sitting the wings are folded and colour resembles a dead leaf, in which red and brown alternate with spots of scales similar to dew-drops. Besides, a mid-rib, lateral ribs of leaf, and black and mouldly spots are also found. The predatory Praying mantis black and moudly spots are also found. The predatory Praying mantis also resembles a leaf.
Many of the walking stick insects (Phasmidae) are also good mimics with their slender body, attenuated limbs, sympathetic colouration and slow movement.
Australian fish, Phyllopteryx eques resembles like fronds of seaweed, due to presence of leaf-like cutaneous outgrowths over the body.
(b) Warning mimicty
In this are included such forms which mimic the apparently harmful creatures, though in itself it is entirely harmless.
This type of mimicry is helpful in self-defence, because by imitating these are able to delude and frighten the enemy and escape themselves. For example: among reptiles, certain snakes of the family Elapidae are deadly poisonous and are beautifully coloured.
Each of these coral snakes is mimicked by other species of harmless snakes belonging to different genera so that it renders the imitators practically immune from attack. Non-poisonous hog-nose snakes (Heterodon) are capable of flattering the head rendering it triangular like the hood and hiss so as to show that they are dangerous.
Among insects also there are examples of warning mimicry. Clear winged moth. Sesia crabroniformis mimics to the dangerous wasp Vaspa crabro. Rower flies are brilliantly coloured resembles the wasps and stinging bees.
In some butterflies, caterpillars, peacock etc. possess black spots on their wings or body. Their sudden display by the animal at the time of danger frightens of insectivorous birds.
The butterfly of genus Thecla exhibit a dummy head as the hind end of the wings by converging colour stripes on the wings and having antennae-like appendages on wing tips.
2. Aggressive Mimicry
It is shown by certain carnivorous forms. In this case the imitation is not for protection but to attack and prey upon other animals.
The aggressive mimicry is divisible into:
(a) Concealing Mimicry and Alluring Mimicry
(a) Concealing mimicry
Here the animals develop cryptic colours so as to blend with the surroundings.
Some of the spiders found on golden-rod and other flowers, with their yellow bodies, so harmonize with the flowers where they rest that they are invisible to the visiting insects which form the spider's prey. Other spiders resemble oak galls and other vegetable growths, yet others the droppings of birds. These are all instance of concealing aggressive mimicry.
(b) Alluring mimicry
In this type mimics advertise themselves and allure or attract their prey. Some species of spider which resembles an orchid blossom both in colour and form; the resemblance is an alluring one and is advertising rather than sympathetic.
Certain African lizards are protectively coloured except for a brilliant coloured spot at the corner of mouth which attracts insects.
Ceratophrys, the American frog, sits still and moves one finger of the hand. This arouses the attraction of other animals, when they attempt to capture the apparent prey, are preyed upon by Ceratophrys.
3. Simulation of Death or Conscious Mimicry
Certain animals exhibit conscious imitation and on the approach of danger behave as if they are dead. The common example is the American opossum, Didelphis, which poses to have been dead-when it is attacked by an enemy. Whether it is an international performance or whether the animal faints from fright is not known. Many insects such as hard-bodied beetles drop down like a pebble when attacked and to be seized.
Conditions for Protective Mimicry
Wallace has given the conditions which must be fulfilled whenever protective mimicry occurs, they are:
1. Imitative species must occur in the same area and occupy the same station as the mimicked.
2. The imitators are always more defenseless.
3. The imitators are always less numerous in numbers.
4. The imitators differ from the bulk of their allies.
5. The imitation is external, never extending to internal characters.