DRAGONFLIES   Leave a comment

 

Definition: any of an order (Odonata) or suborder (Anisoptera) of large insects, harmless to people, having narrow, transparent, net-veined wings and feeding mostly on flies, mosquitoes, etc. while in flight.

Among the most beautiful and useful of all insects is the dragonfly. It has thin silvery wings. Its body may be steel blue, purple, green, or copper. The dragonfly eats mosquitoes, flies, and other insects harmful to man.

The dragonfly lives on or near the water. It is a quick-darting insect that flies swiftly from place to place. Sometimes it changes its direction so quickly in mid-flight that its sudden movement is hard to follow with the eye. It can also hover over a lake or stream as it looks for food.

The dragonfly’s wings are from 2 to 5 inches long. The body is about 3 inches long. Its six legs are far forward and close together. The dragonfly can curve its legs to form a basket. It uses this basket to scoop insects from the air. Then it puts them into its jaws. These jaws have strong teeth.

Two great eyes cover most of the head. Each eye has from 20,000 to 25,000 tiny eyes joined together. With these big eyes it can see its prey easily.

Dragonflies and Damsel Flies

There are two large groups of these insects the dragonflies themselves and the damsel flies. The dragonfly darts with the speed of an express train. Some can fly 60 miles an hour. The two rear wings are larger than the front pair. They are held outspread when the insect lands. The damsel fly is more slender. It flies more slowly and lazily. The wings are the same size. When the insect rests, the wings come together over the back, like a butterfly’s.

The dragonfly begins life as a water insect. Then it is called a nymph. The female lays her eggs in the water. As she flits over the pond again and again she dips under water to wash off the eggs. Some species lay their eggs in long strings on water plants. Such a string may have 100,000 eggs.

The damsel fly cuts a slit in the stems of water plants. Then she puts her eggs in the opening. She uses a part of her body called an ovipositor to do this. (The word ovipositor means “egg depositor.”) Sometimes the damsel fly goes under water and walks about looking for a good cradle. The male may go with the female on this trip.

Life Cycle of the Nymphs

The nymphs hatch out of the eggs in one to four weeks. They are half an inch to nearly 2 inches long. They are flat, dark creatures and have long legs. They hide under rocks and in the mud. There they wait to jump on a careless insect or even a small fish. These nymphs are as fierce in the water as the grown flies are in the air. They have a strange way of catching their prey. The underlip has joints. It is very long, with a pair of hooks at the tip. They shoot this lip forward and catch the insect on the hooks. When they are not using the underlip they fold it over the face like a mask.

The dragonfly nymph breathes by drawing water into the back part of its intestine. Tiny air tubes take out the oxygen. The nymph then pushes out the water in quick spurts. In this way it drives itself forward, like a jet-propelled air plane The damsel-fly nymph has three leaf like gills at the end of its body. These gills take in oxygen from the water.

As the nymphs grow they shed their skins ten to 15 times. Depending on the species, dragonflies live from one to four years as nymphs. The length of their lives depends upon the species. In winter they sleep in the stream bed. The following spring the life cycle begins once again. When they reach the adult stage, dragonflies live only a few months.

Dragonflies are members of the order Odonata. The dragonflies proper belong to the suborder Anisoptera (from two Greek words meaning “unequal wings”). The damsel flies belong to the suborder Zygoptera (“yoke wings”). There are about 2,500 species scattered over the world. North America has about 300 species. One common dragonfly is known as the mosquito hawk (Anax junius). It is bright green, with clear wings about 2 inches long. The ten spot skimmer (Libellula pulchella) has three blackish-brown and two white spots on each wing. Only the male has the white spots.

Ruby spot, insect (Hetaerina americana) member of the Odonata family.

Black-wing, insect (Calopteryx maculata), member of the Odonata family.

The ruby-spot (Hetaerina americana) is a common damsel fly. Its head and upper body are coppery red. The abdomen is green. The male has a ruby-red spot at the base of the wings. In the female the wing is yellowish brown. The black-wing (Calopteryx maculata) is also common.

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Posted 2012/04/07 by Stelios in Education

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