Insect, an invertebrate animal related to spiders, ticks, scorpions, and centipedes. Insects make up approximately 80 percent of the total number of animals on earth. Familiar insects include bees, bugs, beetles, flies, ants, grasshoppers, and butterflies.

The goliath beetleThe goliath beetle has white stripes and grows up to four inches long.

An adult insect has six legs and a pair of feelers, or antennae. It has a jointed body divided into three segments: a head, a thorax, and an abdomen. Most insects have two pairs of membranous wings; some have one pair of wings; still others are wingless.

Insects are very adaptable. They live in a variety of habitats, and are able to withstand extreme climates and harsh environments. Insects are found in the Arctic, in the tropics, on mountains, in deserts, in water, in the soil, and in or on plants and animals. Some are harmful agricultural pests while others carry diseases. Some insects are beneficial, pollinating flowers and crops.

The grasshopperThe grasshopper lives in a variety of habitats.

More than one million species of insects have been classified. Estimates of the total number of species vary from 2,500,000 to 10,000,000. There are approximately 100,000 species in North America.

The fossil record shows that insects existed 390,000,000 years ago. Some of the earliest insects, such as the cockroach, have changed very little. Others, such as the dragonfly, have changed considerably; fossils of dragonflies with 30-inch (76-cm) wing-spans have been found. Besides giving clues to the changes in structure and development of insects, the fossil record shows that they were as abundant 150,000,000 years ago as they are today.