Insects are invertebrates, animals that do not have backbones. Insects belong to a large group of invertebrates known as arthropods. Other members of this group include centipedes, spiders and scorpions, woodlice, crabs and shrimps. Instead of having an internal skeleton, arthropods have a hard outer skeleton. This is made of a light, strong material called chitin that supports and protects their soft inner parts.
All insects have six legs and a body divided into three sections: the head, thorax and abdomen. The chitin covering the legs is jointed to allow the insect to move easily. Insects have a pair of antennae on their heads which they use to smell, touch and pick up sound vibrations. Most insects also have one or two pairs of wings.
Insects have two kinds of eyes: simple eyes that detect changes in light, and compound eyes. The compound eyes are made up of thousands of tiny units, each of which sends an image to the insect’s brain.
This means that insects have good, all-round vision, and are able to sense movements and judge distances very accurately.
After mating, a female insect lays her eggs. The young are usually left to hatch and fend for themselves. Some insects, such as bugs or grasshoppers, look like tiny adults when they hatch. As they grow, they shed their hard outer skeleton several times, after a new one has grown underneath.
Other insects, such as butterflies or bees, hatch out as larvae (caterpillars or grubs). They shed their skin several times as they grow. Then they develop a protective coating inside which they pupate (change into their adult form).
BUTTERFLIES AND MOTHS
Butterflies and moths are a group of flying insects, with wings that are covered with tiny, overlapping scales. These scales give butterflies and moths their bright colours and striking markings. Most butterflies and moths have coloured scales. Others have scales that reflect the light to give an impression of colour.
The colours and patterns of butterflies and moths are used to attract mates, for camouflage, and also to deter predators. Large spots that look like the eyes of a large animal, or bright colours to warn that the butterfly or moth is poisonous, help these insects to avoid being eaten.
Butterflies generally fly during the daytime. They are usually more brightly-coloured than moths and have club-like antennae. Most moths are night-flyers, and have feathery antennae. Adult butterflies and moths have a long, hollow tongue called a proboscis. They use it to probe inside flowers and suck up nectar.
Butterfly and moth larvae are called caterpillars. They feed on leaves until they have grown large enough to pupate. Then they spin a protective cocoon of silk around their bodies, inside which they completely change their structure, and finally emerge as adults. Some may migrate to warmer climates when winter comes, returning to breed and lay eggs.
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