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Flying Dragons of the Sky
DURING hot, midsummer days, the air above fields and ponds becomes the stage for some of the most amazing fliers in insectdom-the dragonflies.
With their two pairs of long wings glistening in the sun, you can see dragonflies flashing back and forth, looping, turning and diving at will. One moment they will be zooming at express-train speed high in the sky, then, the next, swooping down to skim the surface of a pond. These marvels of creation can even fly backward or hover in midair like a helicopter.
But the sun-loving dragonflies do not fly simply for the enjoyment of it. These aerial dynamos ply their skills to feed an insatiable appetite. In fact, Mr. Dragonfly can eat his own weight in half an hour and still be hungry.
When hunting a meal to appease their appetite, dragonflies exhibit distinctive habits. Some species search over large areas. Others have set paths that they follow generation after generation. Larger dragonflies stake out territories for themselves and drive off other dragonflies by wildly clattering their wings. Sometimes if an invading dragonfly is bold and is not intimidated by the clattering, it will be met head to head. Hovering together menacingly, these two will stay in that position while rising straight up into the sky.
Whether they take to roaming or settling in one spot, dragonflies stay alert for their favorite diet: mosquitoes and gnats. They also find tasty meals in moths and horseflies. Because of their long, slender, needle-shaped body, many persons have believed that dragonflies sting, but this they do not do. They are not only harmless to man but also very beneficial because of their devouring mammoth quantities of flies and mosquitoes.
When a dragonfly zeros in on these insects, they are completely outmatched. Equipped with six spine-fringed legs that are bunched together like a basket, dragonflies scoop prey out of the air and suck their bodies dry while racing after another victim. So swiftly do they gobble up prey that dragonflies have been known to eat forty horseflies in two hours. One dragonfly was found with its mouth gorged with one hundred mosquitoes! No wonder these voracious insects have earned the name "flying dragons."
Mating, and Life Underwater
But there is a time when dragonflies pay less attention to eating and more to their airmanship. This is during the mating season. Rival males, seeking the attentions of a female, take to the air to do battle. Their aerial duels feature some of the most brilliant air maneuvers of any living creature. Some species are more moderate, though, and perform a sort of courtship dance.
Once they have found a mate, the males literally carry off the female. To mate, dragonflies fly in tandem, that is, the male holding the female by the back of the head while flying through the air. As the female is to mate, she extends the tip of her abdomen to the male's second thoracic segment and receives a sperm capsule.
After her eggs are fertilized, the female deposits them on a pond's surface or in aquatic weeds. Exactly how many eggs a dragonfly lays is open to question; but there have been found as many as 110, 000 eggs in a single cluster.
The eggs lie in the water or weeds a few days. Then the offspring begin to emerge. And strange creatures they are. Other than being born with hefty appetites, these creatures, called nymphs, resemble the parents very little. They have gills in the thin walls of their intestines. These gills not only absorb oxygen, but, in times of trouble, give the nymph quick getaway power. When alarmed, the nymph just lifts its legs off the bottom of the pond, expels a jet of water through the gills, and rockets forward several inches.
Perhaps the most unusual feature of the nymph is its manner of catching food. Unlike its fleet parents, the nymph is sluggish. So it waits for a mosquito larva or minnow to swim close by. Then, suddenly, it shoots out an underlip hidden beneath the head. Sharp claws at the tip of the underlip grasp the unwary prey and pull it to the nymph's mouth. This underlip, which is hinged and elongated, operates similarly to the human arm. The middle hinge is like the elbow, allowing the underlip to swing back and forth easily.
When the underlip is not in use and is folded back under the body, an unusual thing happens. The claws cover the nymph's face like a bandit's mask. An appropriate costume for these tiny submarine creatures!
Life in the Sky
Many nymphs among the nearly 5, 000 species of dragonflies complete their underwater life in one year. Others, however, may take from two to five years. During this time they pass ten to fifteen successive stages of molting. Many changes take place: the number of six-sided lenses in the compound eyes increase; the antennae gain new joints; the legs lose their hairiness; the wing pads appear on the thorax. But these changes are merely a prelude to their transformation as adult dragonflies.
The nymph's final step to being a creature of the air usually begins at night. It climbs out of the water and clings to the bank or to a stem. Twelve hooks, two on each foot, secure its hold. Here it remains motionless for some time as the body completes the metamorphosis.
Finally a rent appears on the back side of the thorax and the disheveled dragonfly struggles out of the nymphal shell. At first its four wings are damp and folded back like a fan, but steadily they are pushed open by blood swelling the vast network of veins running through the transparent tissues.
Also the colors of the newly emerged dragonfly are faint. But they intensify until the dragonfly rivals even the butterfly and moth in beauty. Its colors range the spectrum of the rainbow-brown, lavender, ultramarine, green, azure blue, scarlet, crimson, lilac, cerulean blue, red and ivory white.
The dragonfly will wait about five hours after leaving its armor-like shell to allow its wings and body to harden. Once the wings are able to carry it in flight, the dragonfly darts into the air. Never again will it use its legs to walk. It has become a creature of the air.
Powerful Flier
The largest dragonfly today is a tropical species having a wingspan of seven and a half inches. It ranks as one of insectdom's best and strongest fliers. In fact, this most accomplished insect aviator has been known to fly fifty to sixty miles an hour!
The power for the wings is supplied by motor muscles that comprise one quarter of the dragonfly's entire weight. These muscles, vibrating the wings 1, 600 times a minute, enable dragonflies to cover huge distances. Such powerful fliers are they that ship passengers have observed them winging their way over the ocean 175 miles off the coast of Africa. One species settled on an island that lay 200 miles across open sea!
They fly the greatest distances when drought or food shortage drives them into migrating. These migrations sometimes attain fantastic proportions. In 1839 millions of them blanketed the skies as they followed rivers and streams over most of Europe. In the United States, swarms of them migrated to the South in 1881, literally darkening the skies.
But these great fliers must be ever watchful. They are in constant danger from birds, frogs and fish. Against such predators dragonflies have speed and keen sight. Their bulging eyes, which cover the better part of the head, can scan far into the distance. The Creator designed them in such a way that each eye contains as many lenses as the eyes of 15, 000 men! They can also see in virtually every direction at the same time. And they are farsighted, allowing them to spot a mosquito thirty feet away.
With such vision dragonflies can dodge almost any pursuer, including man. Trying to catch these dexterous fliers can be quite a task. But Japanese children have discarded the net in favor of ingenuity. They attach tiny pebbles to the ends of long hairs and throw them into the air where dragonflies are circling. When one of the insects pounces upon the passing stone, the hair twists about its body and the weight of the pebble grounds it.
Even though these zestful creatures are able to elude most enemies, those in the temperate zone eventually get caught by the chilling winds of autumn. Life for the dragonfly is short, lasting only the warm months of spring and summer. In the fall you will find them clinging motionless to stems or leaves, numb from the cold. Flying is done only during the warmest part of the day. The first frost brings down the curtain for them, leaving the air above the fields and streams devoid of their fascinating presence.
But the chain of life does not stop. Nymphs, protected beneath the ponds and streams, continue to mature. With the hot weather, they will emerge to become a new generation of the dragons of the sky.
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