The Insects are the most diverse and important group of animals on land. There are more species of insects than all other land animals put together. Insects live in all habitats and occupy any microhabitat you can imagine. They can be predators, prey, parasites, hosts, herbivores, or decomposers.
Insects are members of a larger group called arthropods (which also includes arachnids, myriapods, and crustaceans). All arthropods have a rigid exoskeleton, and legs that are jointed (arthropod means "jointed foot"). In order to grow, arthropods have to shed their whole exoskeleton all at once; this is called "molting." All insects have bodies which are divided into three sections: the head, thorax, and abdomen. In some insects these sections are fused together so they may be hard to tell apart, and some baby insects (called immature) do not have all three sections until they become adults. Nearly all insects have a pair of antennae on their heads. They use their antennae to touch and smell the world around them. Adult insects (and most immatures) have six legs that are attached to the middle section of the body, the thorax. Insects are the only arthropods that have wings, and the wings are always attached to the thorax, like the legs.
All insects lay eggs. There are two ways that insects grow: complete or incomplete metamorphosis. Insects that have complete metamorphosis have babies that look very different from the adults and often eat very different foods than adults. Butterflies, beetles, and true flies are some of the groups that have complete metamorphosis. The babies are called larvae. Caterpillars and maggots are examples of insect larvae. Larvae often have soft exoskeletons that stretch so they can grow fast, and they go through a resting stage called a pupa before emerging as an adult. Insects that have incomplete metamorphosis have babies that look like small adults with no wings. They usually eat the same kind of food as the adults do. Grasshoppers and cockroaches are two kinds of insects that have incomplete metamorphosis.