Wednesday, April 23, 2008

Insect

Insect are members of the phylum Arthropoda, class Insecta, the largest and most diverse class in the animal kingdom. Insect have three body divisions; head, thorax, and abdomen; and six legs borne as an adult. Because of their small size, ability to fly, rapid reproductive rate, and external skeleton, insect are highly successful animals that have exploited every habitat except the polar ice caps. The external skeleton is coated with a waxy layer that helps insect converse body moisture. The small size of insects aids in their dispersal to more favorable habitats. Thrips and aphids are carried by frontal systems for long distances. Small insects have been collected by airplane at 3,000 m (10,000 ft). Migratory butterflies and locusts may fly hundreds of kilometers in a few weeks.


Insect display almost every color, from drab, dull brown and black, to iridescent blues, and reds, and purples, to the metallic greens, blues, yellow and reds of some Wasps and Bees. Sizes vary from tiny mymarid wasps less than 1 mm (0.04 in) long to huge beetles or slender walking sticks up to 30 cm (12 in) long. Shape is equally variable. For example, legs may be adapted for walking, jumping, running, clinging to hairs, swimming, spinning silk, carrying pollen, hearing, or they may be absent.


Feeding and Digestion


Insects obtain food by a variety of methods, including biting, lapping and sucking. Carnivorous insects such as the praying mantis catch and chew their prey. Some wasps paralyze their prey with veronomous stings, lay their eggs in the bodies, and provide a living food supply for their young. Termittes are able to digest and receive nourishment from wood because tiny protozoan within their digestive system "predigest" the cellulose in the wood.


The digestive system is essentially a tube that begins with the mouth and is divided into a pharynx; esophagus; crop, stomach (midgut), and intestine (hindgut); colon and rectum. The midgut has glandular outgrowths, the gastric ceca, which secrete digestive juices. The Malpighian tubes remove nitrogenous waste from the blood; the blind tubes empty into the hindgut.

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