Insect Wings in General

The insect wing is said to be a unique organ of flight . The insects are the only animals that have wings originally evolved for flight, since bird and bat wings are only modifications of pre- existing limbs. Their wings are believed to have originated as flat expansions of the sides of the thoracic segments. They were probably useful in gliding.

Full sized and functional wings occur only in adult insects with the exception of the Mayflies. However, developing wings may have been seen as small, fleshy pads on the thorax of immature insects called nymphs in the Exopterygota and the pupae of the Endopterygota

On each wing, there are thickened lines and ridges called veins. The area of the wing membrane between the veins are called cells.

Wings are important in identifying and classifiying insects as there is no other set of structures in studying insects more significant. Each order and insect family has distinctive wing shapes and features. In many cases, even species may be distinguished from each other by differences of color and pattern on the wings.

Most insects fold their wings when at rest. But Dragonflies and some Damselflies rest with their wings spread out horizantally. Some moths such as the Caddisflies, Stoneflies, Alder Flies, and Lacewings hold their wings sloped rooflike over their backs. A few moths wrap their wingsaround their bodies. Many flies and most butterflies close their wings together straight upward over the back.

Many insects can hover in one place as a helicopter does. Some expert insect fliers that often hover in one position such as Dragonflies, Sphinx Moths, Bee Flies, and Flower Flies. Wasps and Bees often hover as well when seeking prey or in front of a flower. These same insects can even fly backwards for short distances.

Many times the shape of the wings correlate with the type of flight an insect takes. The best flying insects tend to have long slender wings. In many of the Sphinx Moths, the fore wings are large and sharply pointed, forming with the small hind wings a triangle that is suggestive of the wings of fast, modern airplanes.

Actually a more important correlation is the great power and size of the flight muscles.

In the powerfully flying insects, the wings are most beautifully adapted for the stresses and aerodynamics of flight. The veins are thicker, stronger, and closer together toward the front edge(called the "leading edge") and thinner yet flexible toward the rear edge (called the "trailing edge"). This makes the insect wing an excellently constructed "airfoil" capable of exerting both "propulsion" and "lift" while minimizing "drag".

Laboratory expiraments show that not only does the wing beat vary in different species but can vary in one individual insect at different times - much like people! In general, the frequency is dependant upon the ratio between the power of the wing muscles and the "resistance" (weight) of the load. Largewinged, lightbodied butterflies may have a wing beat frequency of 4-20 per second whereas a small-winged, heavy-bodied flies and bees beat their wings more than a 100 times a second and even Mosquitoes can beat up to 988-1046 times a second.

Here's a listing of wing beats per second:

Many have speculated about the speed of an insect's flight and thus many tall tales have been told and retold. It is generally difficult to estimate the speed of insects in flight. But there is little doubt that in nature, most insects can go faster than controlled experiments. Such as the Dragonflies possibly making 33 miles per hour. The figures that are now most widely accepted for their speed under controlled circumstances are in the following table, in miles per hour:

With all this high speed business of being a flying insect, people may have wondered if insects ever get tired. They do but they demonstrate a terrific resistance to fatigue. A Drosphila Fly has been known to fly continously for 6.5 hours and a Schistocerca Locust for 9 hours. Wing muscles have made more than one million successive beats before tiring yet in contrast, the worker Honeybee may tire after 15 minutes of flying.

Purpose of Flight in Insects

Besides the need to search for food or a resting habitat , there are other purposes for insects to remain in flight. With wings, insects were able to spread over the globe; if conditions became unfavorable in one place, they simply took to the air to find another. Flight has given them an advantage over landbound animals in being able to forage widely for food, make good their escape from enemies and search actively for mates.

Some are very unique from other species or members in their order. Take for example, the Drones (the males of the Honeybees) whose only duty is to fertilize the queens when they are aloft in the marriage flight. After performing this one task they die, their genital organs having been left in the body of the females. Many swarms of social insects are mating swarms. Only the ants, among the social Hymenoptera, mate during swarming flight. Their flights may consist of hundreds or thousands of males and females. Termites have similar flights during which males and females pair off and begin new colonies.

Many insects use their sense of feeling warm temperatures to assist themselves in flight. A moth ususally goes through a remarkable ritual before taking to the air. It beats its wings so rapidly that they blur like like the whirling of propellers of an airplane. Suddenly, after several minutes, it takes off. If a moth is captured before it has completed the ritual and then dropped, it is unable to fly but falls to the ground instead. Obviously, the moth generates heat through the flexing of its flight muscles. If a moth is kept in a heated cage, it does not need to rev up its motor but instead can take flight immediately. For this system to work, the moth should possess a mechanism for gauging temperature, but scientists do not as yet know where these heat- sensitive cells are located.

Many insects rely upon the direction of the sun's rays as a sort of compass. This can be easily demonstrated by a simple experiment. Place a light-tight box over an ant carrying food back to its nest and keep it imprisoned for a few hours. When the box is removed, the ant will not continue on its former course, but will start off rapidly in a new direction. This new route will differ from the old by exactly the angle that the sun has shifted across the sky during the time the ant was imprisoned.

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Last modified: Wed Jul 2 10:55:48 PDT 1997

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