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What is the Buzz About Insect Wings?
Anyone who has paid the least bit of attention to insects knows that these creatures have wings. The presence of wings and the ability to fly are among the biological attributes that make insects such successful animals. Wings allow insects to escape enemies, find food and mates, and move to new habitats.
Bats and most birds also have wings. But in terms of number of species with wings and diversity of those structures no other group of animals compares to insects. Both immature birds and immature insects are unable to fly. In birds and in some insects immature individuals have wings but cannot fly, because the wings are not yet developed sufficiently for that function. However, in many insects the immature forms do not have wings at all. In this case, the wings are formed when the insect is in the pupal stage. So dramatic is this change in form that scientists call it "complete metamorphosis."
Wings were such an obvious attribute of adult insects that the Greek word pterum has been incorporated into many insect order names. For example, butterflies and moths are classified as Lepidoptera, a word that literally means scale wing. Beetles are Coleoptera or sheath wing. The forewings of beetles are hard, shell-like structures that protect the membranous hind wings when the beetle is not in flight. In like fashion, bees and wasps are Hymenoptera because of their membrane-textured wings. Flies possess only two wings and are named Diptera.
In general, insects have four wings. But some adult insects have no wings at all. So the presence of wingless insects brings up the question of whether or not insects have always had wings. Most scientists believe that the earliest insects on the earth were wingless. Somewhere in geologic history wings evolved and were modified into the many types of wings present in insects today.
Silverfish and firebrats are wingless insects that are part of the current fauna on the earth. These insects are probably some of the oldest still in existence. There are also wingless insects that are much more modern in origin: fleas and lice, for example. Both of these ectoparasites may have evolved from insects that were winged. Why did this happen? One explanation is that because fleas and lice live in the fur and feathers of a host animal the presence of wings just got in the way when the insect moved. In other words, the wings were more of a disadvantage than an advantage to the insect, so over time the wings were lost.
When it comes to wings, a few insects have a use-'em and leave-'em approach. Termites and ants are examples of such a system. In both of these social insects most of individuals in a colony are wingless, only the reproductive forms have wings. The wings are used during mating flights and for flying away from the home nest to try to establish a new colony. Once these activities have been completed the insect sheds the wings. Wings just get in the way in the close confines of the tunnels of an underground nest where they serve no function.
When not being used for flight, most wings are a bit of a problem to insects. So one of the adaptations of insect wings has been the ability to fold. Some insects, such as dragonflies and butterflies, can't fold their wings. Consequently, when you look at these insects you can see both pairs of wings. In some other insects, the back pair of wings folds fan-like. In beetles, the back wing that is membrane-like is folded up and tucked under the hardened front wing. So when you look at a beetle the only wings that you see are the front wings that close and form a cover over the abdomen of the body. When a beetle is flying, and right after landing, both pairs of wings are visible.
Grasshoppers are similar to beetles in that the front wings are leathery and when the insect is at rest the folded back wings are hidden. In some of the insects that cover one pair of wings when at rest the always-visible front wings are colored so that the insect blends into the environment. In some instances, the back wings might be a bright color or even marked with eyespots. Such wings, when exposed, can be used to startle a predator. So in the rough-and-tumble world of insect biology, flying away from predators is a good thing, but using wings to avoid predators by blending in or scaring them away is just icing on the cake when it comes to survival.