|Snakes are well known for their poisonous bite, but in fact their venom is designed for catching prey, and not for defending the snake. However, snakes are often victims of chemical defenses, as are birds and mammals. This is because the most common users of chemical defenses are insects. Vast numbers of insects are consumed every day, as they are a major food source for many types of animals, but poisonous chemicals help defend them from hungry birds, frogs, toads, lizards, and even other insects. Frogs are another common user of chemical defenses, and especially well known are the poison arrow frogs of Central America.||
|Insects have also evolved an impressive number of "mechanical" defenses. Mechanical defenses, which are designed to prevent encounters with predators, include camouflage and mimicry. Camouflage provides an advantage both when trying to avoid predators, and when stalking prey--two situations in which an animal would want to be invisible. Insects are the most well-known group to use camouflage, and since insects live surrounded by plants, they usually evolve plant-like forms as a camouflage.|
|An effective camouflage strategy is to resemble the common inedible objects found in a forest. This type of protection is especially common in the tropical rainforest, where insects blend in with the infinite variety of bark, twig, thorn and leaf shapes.||In temperate forests, camouflage becomes more difficult. Tropical forest plants look fairly similar all year, while plants in the temperate zone have very different appearances in the spring, summer, fall, and winter. For an insect to be effectively camouflaged through several seasons, it needs to be able to change its protective coloration.|
|Many birds, such as grouse, which spend a lot of time on the ground where they are vulnerable to predators have developed colorations and patterns which help camouflage them. Photo by Maya Walters.|
|Color is not the only way to hide: taking on the actual shape and texture of a leaf or twig is sometimes a much more effective type of camouflage. Stick insects of the tropical cloudforest, and inchworms in temperate regions both bear a convincing resemblance to twigs. Geometrid moths have the colors, shapes, and patterns of dead leaves, and are virtually invisible when they land on fallen leaves on the tropical forest floor. For this appearance, however, they sacrifice an aerodynamic wing shape. The huge investment they have made in this camouflage indicates that they must be a very desirable prey indeed.|
|The flattened, spiny shape of this insect is typical of "stick" and "leaf" insects which attempt to mimic the shapes of natural vegetation. Photo credit Corel Photo Clipart CD.||When approached by a predator, the worst thing a camouflaged insect can do is move. If disturbed, the geometrid moths, stick insects and many other hidden insects will attempt to remain motionless. A sudden movement would call attention to them, and destroy their resemblance to an inanimate object. For this reason, many camouflaged insects are nocturnal, moving only during the night when they can't be easily seen.|
|When these insects are forced to move, they try to be inconspicuous about it. A stick insect will step away rather grudgingly when disturbed, rocking back and forth as it does so, to give the impression of a twig moving in the wind. The moths that imitate dead leaves will let go of a branch and simply fall gradually to the forest floor, in the same way that a true dead leaf would.|
|Mimicry is a different type of camouflage. Animals do not try to blend in with their surroundings, but instead mimic a different type of animal. A number of harmless snakes have evolved very similar coloration to highly poisonous snakes. Many types of harmless, stingless flies have evolved a very similar appearance to bees and wasps.|
This moth has colors and patterns that mimic those of a bee. At first glance, especially when in flight, the moth looks enough like
a bee to discourage most predators. Photo by Maya Walters.
Bees and most wasps are easily recognizable because of their patterns of black and yellow stripes, and most predators learn quickly to avoid them because of their painful, often poisonous stings. A fly that is really quite harmless can take advantage of the wasp's reputation by mimicking it's appearance. The fly might actually make a good meal, but when a predator sees its wasp-like pattern, it stays away.
|The stings of those wasps and bees are a form of both a mechanical defense and a chemical defense. The venom injected by the stinger is a specific mix of chemicals, which usually cause pain and swelling in the predator foolish enough to try to catch them.||Ants, bees, and wasps are the most commonly mimicked insects, because they are some of the most common users of stings with painful chemical defenses. Even stingless ants and bees have chemical defenses: many ants can spray formic acid from their abdomens, and some bees have glands which produce corrosive secretions. The chemicals used by ants, bees, and wasps are all produced by the insects themselves.|
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