Animals in Disguise: An Introduction to Camouflage and Mimicry

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This flounder is almost invisible against gravel on the seabed. Photograph by Moondigger.

Escaping predation and finding food are challenges faced by all living creatures. Hiding and hunting are obvious solutions, but many animals – both prey and predator – have evolved a more subtle approach. By disguising themselves as other animals, plants or even inanimate objects, mimics and camouflaged creatures have an evolutionary advantage over their less duplicitous counterparts.

Camouflage: Hiding in Plain Sight

A camouflaged animal avoids detection by assuming the appearance of its surroundings, allowing it to evade predators or lie in wait for prey. Well-known examples are zebras and tigers, both of which have evolved stripes that make them difficult to discern amidst the long grass or jungle plants of their respective habitats. Stick and leaf insects, whose entire bodies resemble parts of the plants among which they live, enhance their disguise by remaining motionless for hours at a time, or even rocking gently from side to side, as if swaying in the breeze.

Many insects, birds and fish are almost invisible in their natural homes, so closely do their colors, patterns and textures resemble sand, rocks or the seabed. There are insects that look like bird droppings, and marine shrimps whose bodies are almost totally transparent in water.

Some animals alter their appearance to match seasonal changes in their surroundings. The arctic hare, for example, has brown fur during summer but turns white for the winter as camouflage against the snow, as do the feathers of the ptarmigan. Other species can pick and choose their disguise at will – sea urchins have been observed carrying pebbles and seaweed on their backs, while hermit crabs camouflage themselves with live sea anemones attached to their shells. When moving to larger shells as they grow, these crafty crustaceans have even been known to take their favorite anemones with them.

Batesian Mimicry: “Sheep in Wolf’s Clothing”

Whereas a camouflaged animal resembles its surroundings, be that a plant or an inanimate object, mimics have evolved to look like other animals. Mimicry is widespread in the animal world and has been classified into numerous types; the most common are termed Batesian, Müllerian and aggressive.

Batesian mimicry is probably the best known of the three. These mimics deter potential predators by resembling another species that is toxic, dangerous or in some other way an undesirable meal. However, Batesian mimics have none of their models’ unpalatable attributes, and for this reason have been described as “sheep in wolf’s clothing”.

The harmless beetle Clytus arietes mimics a stinging wasp. Photograph by Rob Knell.

Batesian mimicry was named after the 19th century English naturalist Henry Walter Bates, who studied the phenomenon among butterflies in the Amazonian rainforest. It is still most often observed in insects, though animals such as fish, molluscs and crustaceans are also known to impersonate noxious species to avoid predation.

Sounds as well as appearances can be mimicked. Certain species of moth emit ultrasonic warning signals similar to those produced by tiger moths, which are toxic to bats. Bats learn to associate the tiger moths’ warnings with an unpleasant taste, and in a study reported in the Proceedings of the National Academy of Sciences of the United States of America were found to avoid eating both genuine tiger moths and harmless tiger moth mimics.

Müllerian Mimicry: Convergent Evolution in Action

During his work in Brazil, Henry Bates was surprised to find that some noxious butterfly species resembled other (or even several) noxious species. Whereas Batesian mimicry has an obvious benefit for the mimic, this type of mimicry was more difficult to explain. How is it advantageous for one harmful species to mimic another? This question puzzled zoologists until German naturalist Johann Müller suggested the answer in 1878. What has become known as Müllerian mimicry is a form of convergent evolution – the process by which unrelated species come to acquire similar characteristics.

These eight butterfly species all taste unpleasant to predators, and have evolved similar coloration. Image from PLoS Biology.

Müllerian mimicry arises from the fact that predators learn to avoid unpalatable prey on the basis of their appearance. Any noxious prey that looks similar to a noxious species that the predator has already learned to avoid is therefore safer than one that looks different. This may explain why bees and wasps, which both possess painful stings, also both have distinctive yellow and black striped coloration.

Aggressive Mimicry: Helping Predators and Parasites

Aggressive mimics are predators that resemble other species to lull their prey into a “false sense of security.” By appearing to be a harmless cleaner fish, the bluestriped fangblenny can mingle freely with its coral reef prey as it chooses its next meal, while the jumping spider Myrmarachne melanotarsa resembles the ants on which it feeds.

Certain parasites use aggressive mimicry to gain access to their host. An unusual example is the cuckoo, which lays its eggs in the nests of other bird species; these are accepted by the hosts – and hatched and raised as their own offspring – because they have evolved to resemble the hosts’ eggs.

Cuckoo eggs (if not their chicks) resemble those of their host species. Photograph by Per H. Olsen.

The “Mimic Octopus”: Master of Animal Disguise

Imitating the appearance, behavior, sound or smell of another animal, a plant or an inanimate object can help prey avoid being eaten, predators catch food and parasites invade their hosts. Such subterfuge is widespread throughout the animal kingdom, though possibly the greatest master of disguise is the octopus Thaumoctopus mimicus. This resident of the seas off Indonesia can camouflage itself by altering its skin color and texture to match its surroundings, mimics the shape and movement of flounders when swimming, and when motionless on the seabed assumes the appearance of colonies of sponges, tube worms or other sessile marine animals; in all, it has been recorded to mimic 13 different species that share its habitat. T. mimicus may be an extreme example, but in the world of animal intrigue, even a little deceit can go a long way.

Sources

Barber, J., Conner, W. Acoustic Mimicry in a Predator–Prey Interaction. Proceedings of the National Academy of Sciences of the United States of America. Accessed 06-15-11

Cöté, I., Cheney, K. Animal Mimicry: Choosing when to be a Cleaner-fish Mimic. Accessed 06-15-11

Hanlon, R., Conroy L-A., Forsythe, J. Mimicry  and Foraging Behavior of Two Tropical Sand-flat Octopus Species off North Sulawesi, Indonesia. Biological Journal of the Linnean Society. Accessed 06-15-11

Nelson, X., Jackson, R. Aggressive Use of Batesian Mimicry by an Ant-like Jumping Spider. Biology Letters. Accessed 06-15-11

Stevens, M., Merilaita, S. Animal Camouflage: Current Issues and New Perspectives. Philosophical Transactions of the Royal Society B. Accessed 15-06-11

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