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Insect Flight

There are only four group of animals have flying wings. Compare with the pterosaur, the birds and the bats, insects were the first group of animals flying on earth. Having wings is one of the major reasons of  insect's success and they are now dominating the earth. Most insects have two pair of wings, but some are wingless, such as lice, fleas and silverfish, while some have only one pair of wings, like files. Some insects have four wings but the forewings are modified not for flying, as in beetles,  the forewings are for the protection of the hind wings and the abdomen.
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The aerodynamic theory behind the bird's wings and insect's wings are quite different. The bird's wings is similar to the aeroplane wings, a fixed wing model. The air travels a longer distance, i.e. move faster, on the wing top surface and generate a lift and thrust force. This fixed-wing model cannot apply to the insect's wings. Scientists still investigating the details of the aerodynamic theory behind the insect wings. 
How insects acquired their wings in evolution is still not fully understood yet. Once wings became functional flight organs, they subjected to endless modifications. Dragonflies and Lacewings fly with two pairs of wings, although the ways they fly are totally different. In orthopteroid insects and beetles, their front pair of wings are for protection only. They fly only with hind wings. For the butterflies, moths, bees, wasps and some cicadas, their forewings coupled with hind wings in flight. For flies and mosquitoes, their hind wings had been reduced, fly only with forewings.
For those insects fly with forewings coupled with hind wings, the coupling methods are different for different insect orders. In evolution, insect wings coupling evolved a few times. In wasps and bees the posterior margin of the forewings is engaged by a row of small hooks on the anterior margin of the hind wing. In cicada, forewing and hind wing are hooked together by a grooved coupling along the hind wing costa and forewing margin. In butterfly, there is the enlargement of the humeral area of the hind wing which is overlapped with the fore wing. The humeral vein strengthened the hind wing overlapped area so that the two wings coupling better.
Dragonfly, damselfly and mayfly wings cannot be folded backwards over the abdomen. Their wings can only be held in outstretched position or raised upwards. Other insects can fold the wings back along the abdomen. This affect their life style a lot. Basically a dragonfly does not walk or crawl.

Why some insects loss their capability of flight?

Capability of Flying is one of the major reasons that make Insects as the most success species on earth. Why some of the insects species lose their capability if flightiness during their evolution? 

If insects live in the environment that they will be fitter by losing their wings, in the evolution point of view, they will lose their wings. The reason for losing of wings is similar to that of losing eyesight. If we check the animal living in the condition that the eyesight that is not so important, such as in the deep sea and in the caves, most of them are blind. The insects species that loss their wings are usually those in the stable environment, where long distance is not necessary. 

The existing of birds, bats and spider webs change the way how insects wings develop. Before birds and bats (of course and the pterosaurs), insects dominate the air. They are the first animal can fly. When there is the flying predators, unless you have the better flying skin or some other technique to avoid them, otherwise it is better not to be found in the open air. So most of the insects evolved not to fly unless necessary. Most insects fly only when running away from predators or to find their mate. All the insects species now flying freely on air have their very good eyesight to avoid the spider webs. Moths and butterflies even evolved their scale to escape form the spider webs. Moths fly at night to avoid the birds. Wasps and bees have their string as weapon. Butterflies are distasteful and use the mimic technique. Dragonflies and flies have extremely good flying skills. The rest of the insects just choose not to fly. 

Losing of flightiness and eyesight are two of the good examples to show the rule in evolution, the survival of the fittest. Those two capabilities will loss in a few generations and we can see that happen in term of species level. While to gain the two capabilities will need millions of years and in the level of class. 

From this, we can predict that human will loss their capability of give birth naturally. Now we can see that to give birth a baby, for the whole process from fertilize an egg to a baby grow up, we are become more and more depend on the modern medical help. So, after a few tens of generations, human reproduction will be a totally different process.




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Last updated: November 06, 2006.