A group of living things
Insects
Insecta
Six legs, three body parts, about a million known kinds.
Its members' last common ancestor lived about 480 million years ago.
You and insects last shared an ancestor about 580 million years ago (on 11 November, if life's history were one year).
Adult insects have six jointed legs and a body with three parts: head, middle and rear. Scientists have named about one million kinds, which is about three in every four known animals — more kinds than all other animals put together. Surprisingly, their close relatives include crustaceans such as krill and crabs, which mostly live in water.
A hard outer shell covers the body, and it must be shed whole so the insect can grow. Most adults have wings, often two pairs of thin, veined wings. Insects were the first animals that could truly fly, more than 300 million years ago — tens of millions of years before any animal with a backbone could fly. Many are tiny enough to sit on your fingertip.
Insects live almost everywhere on land and in fresh water, from back gardens and ponds to deserts, rainforest tops and polar land. Very few live in the sea, where their relatives such as crabs and krill are much more at home.
Noses on the head
Insect feelers work mainly as noses for smell. They can be thread-like, beaded or feathery.
Breathe through the sides
Most insects breathe through tiny air tubes that open at holes along the sides. In most kinds, blood plays no part in moving oxygen.
Young change shape
Some young hatch looking like small adults. Monarchs hatch as caterpillars, shelter in a case while changing, then come out as butterflies.