Insects make up approximately 80 percent of the total number of animals on Earth.
Insects have jointed bodies divided into three segments: the head, thorax and abdomen.
Fossil records show that insects existed 390 million years ago. Some of the earliest insects, such as cockroaches, have changed very little.
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Instead of internal skeletons, insects have exoskeletons -- tough outer coverings made up of several layers. The most rigid of these layers is composed of chitin, a horny, waterproof substance.
The simple eyes, or ocelli, are located on the head between the compound eyes. The ocelli aren't used for vision, but to detect changes in the intensity of light.
Although insects breathe air, they don't have lungs. Instead, a system of branching air tubes, or tracheae, reaches all parts of the body. Air enters through openings called spiracles.
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Complete, or indirect, metamorphosis follows this developmental pattern: egg, larva, pupa, adult.
Less than 2 percent of all insect species are harmful; but among them, they can cause major crop damage and spread serious diseases.
A general rule of thumb is not to eat any brightly colored insect since it's nature's way of warning predators that this insect is poisonous.
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