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Insects | |
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What is an Insect? We are surrounded by thousands of tiny animals we call Insects. There are more than 800,000 species of insects and still hundreds more are discovered every year.
Most insects have thin wings and must beat their wings rapidly in order to get the lift they need. Bee's wings move forward, backward and up and down. Bees flap their wings over 100 times a second.
How Insects Fly Insects were the first creatures to develop wings. Although many insects now spend the greater part of their lives grounded as larvae, they nearly all take flight as adults when it comes time to mate and spread their kind. Wings are so fundamental to insecthood that they are not mere modified limbs, like bat or bird wings, but part of the insect's back. Their wings are a basic structure of its external skeleton, delicately strutted with passages for air and blood.
Insects simultaneously twist and oscillate their wings; this allows them to hover or even fly backwards. Their wingbeats generally take the form of ellipses and figure eights. A dragonfly beats its pairs of long , slender wings independently, the front ones rising as the rear ones fall. Despite this primitive equipment, the dragonfly is still the deftest of flying acrobats.
As stated in the introduction of Insects, flight begins in the thorax section of the insects as wings and limbs are connected there. In recent years there has been a lot of research as to the various principles of aerodynamics at work in the insect's thorax section ,while it flies. The method of collecting data about flight of an insect is also very interesting. In early years, insects were put in jars and observed . Most recent data has been obtained from studies of insects beating their wings as if flying while glued to a wire,"tethered", which keeps the insects where the experimenter wants them. Aerodynamic and inertial work are calculated from the observed wing movements and the metabolic cost is calculated from oxygen consumption. In insects who display tremendous amounts of wing beats per cycle, it has long been suspected that their beating is sustained elastically like the vibrations of a tuning fork, that kinetic energy lost by the wings as they are halted at the end of one stroke is stored in springs that recoil elastically to provide the kinetic energy for the next. (Alexander, April 1995) Butterflies and Moths
We call the insect in this resting stage a PUPA. The pupa develops a covering called the pupal case. Inside this case, during the long pupal rest, the body of the adult takes shape. Many insects, however, skip some of these stages. The butterfly and the moth take all four forms- egg, larva, pupa, and adult.The crawling caterpillars are the larvae of butterflies and moths. Caterpillars eat so much that their skins become too tight.
All they have to do is split their skins and crawl out in new skins that fit better. They do this 4 or 5 times before becoming pupas. Moth larvae spin thin houses, or cocoons, around themselves for the pupal stage. A butterfly also develops similar covering . Once the adult body is fully formed, the pupal case opens. Out comes the adult butterfly or moth. The wings quickly grow strong in the fresh air. In a few hours, the adult insect can fly away. Insects have many enemies even among other insects. One way they protect themselves is just to hide where they can't be seen. They often hide behind their own coloring. But sometimes the best defense is to fly or scamper away as fast as they can. The butterflies and moths number 140,000 species, exceeded only by the beetles. In size, butterflies and moths vary more than any other insects- the OWLET MOTH is a foot (30cm.) across. But size is not necessary for strength: the MONARCH BUTTERFLY can migrate more than 2,000 miles (3200 km.) yearly. Butterfly Migration Butterflies as well as birds are fine fliers. They can perform aerial acrobatics that a stunt flier would love to copy. But would you believe that these light and graceful creatures can cover long distances? Some species of butterflies migrate in search of warmth. The lovely orange and brown monarch butterfly leaves Canada every fall to fly thousands of miles southward. They often stop for a month in Natural Bridges state park in Santa Cruz (Northern California). Great swarms of them reach the Gulf of Mexico and even farther south. They spend the winter resting quietly in the sun. In the spring they start the long journey back again. As they travel the females lay their eggs on the milkweed plants. The eggs eventually develop into butterflies, who also fly north. Many of the older butterflies do not survive the long journey, but the young, strong butterflies carry on the pattern of migration. Many of these migrations are made over large bodies of water. Another species called the painted lady butterfly, flies across the Mediterranean Sea, all the way from North Africa to Britain or central Europe. It makes the long return journey in the fall. The migrating butterflies travel in huge numbers. Sometimes millions of them fly together. Ancient Insects It is obvious that flying insects were better equipped to escape from the newly arrived amphibians as well as from their older enemies, the spiders and the scorpions, than were their wingless relatives. Insects attained flight fully 100 million years before the first vertebrates- flying reptiles and birds-took to the air. For this long period insects were the sole inhabitants of the air. Insect wings were probably developed from little flaps on top of the leg-bearing locomotion center- the thorax. Even today, all insects are wingless when they hatch out of the egg. Since an insect's external skeleton has no stretch, the growing animal must cast off its old skeleton from time to time and grow a larger one. Primitive wingless creatures like silverfish keep growing and molting throughout their lives, but for winged insects there must be one final molt into winged form, since wings cannot be molted or replaced. Although insects probably flourished earlier, the first readable fossil record appears in the beginning of the Upper Carboniferous, the age of the great coal forests (350 million years ago). Most familiar of these early forms was a large roach and flitting overhead was a MEGANEURA, an immense dragonfly-like creature with wings up to 30 inches (76cm) across. Here also were forms unknown today, like STENODICTYA, which had a pair of rudimentary wings plus two fully developed pairs of wings. The Permian age (270 million years ago) saw the emergence of reptiles like the sail-finned Edaphosaurus at center back. But while these lumbering creatures ruled the land, the insects dominated the air unchallenged by any other winged form-reptile, bird or mammal. Among these Permian species was an early grasshopper, OEDISCHIA, with slender antennae and strong jumping hind legs. In the air above was the OEDISCHIA who was an ancestor of the modern stone fly and the ancestral MAYFLY. Like their modern counterparts, both of these creatures probably had aquatic nymphal forms. With one exception, all of the orders of insects represented in the Triassic age (225 million years ago) are alive today, an example of staying power unparalleled among the higher animals. The ancestor of the CRICKET had wings that were 6 inches (15cm) long, and had a noisemaking apparatus that may have been audible for a mile (1.6 km). Also during this Triassic age, were evidences of primitive SAWFLY and early species of SILVERFISH. In the Jurassic age (180 million years ago), there were roaming dinosaurs like the Allosaurus and the flying reptile Rhamphorhyncus ruling the air. But insects still thrived and with the appearance of the first flowering plant like the Magnolia, as this period merged into the Cretaceous age they undoubtedly flourished on nectar and pollen. Only when flowering plants arose did the insects that specialize in pollinating them such as (what?) Few fossils have been found in this period, mostly familiar forms: a darting DRAGONFLY; a CADDIS FLY on a stump; an EARWIG on a leaf; and a PLANT LOUSE on a magnolia blossom.
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Some flying insects beat their wings so fast to an extreme , such as
the tiny "midge" who beats its wings up to 1000 cycles per second.
