Insect Senses

If insects were as big as we are, some of their eyes would be as large as footballs and their antennae would be up to 2 m (7 ft) long. Fortunately, insects never reach this size, but their senses play a vital part in their lives. For us, sight is the most important sense, and it is for many insects too. Most insects also have a superb sense of smell, and some can hear sounds more than 1 km (3⁄4 mile) away. Insects use their senses to find food, track down a mate, and avoid being caught.

COMPOUND EYES
Unlike vertebrates (animals with backbones), insects have compound eyes. A compound eye is split into lots of separate facets (units), each with its own lens. Each facet works like a mini-eye, collecting light from a small part of the view. Some insects have a few facets in each eye, but horse flies and dragonflies have many thousands. This gives them a detailed picture of their surroundings – although not quite as good as ours.

THREATENING GAZE
This horse fly’s compound eyes cover most of its face. Unlike our eyes, its eyes cannot move, but because they bulge outwards, it gets a good allround view. As well as compound eyes, many insects have three small eyes, or ocelli, on the top of their heads. These eyes each have a single lens. They register light levels, but they do not form a picture.

NECTAR GUIDES
Insects see fewer colours than we do – for example, they are not nearly so sensitive to red. However, many of them can sense ultraviolet light, a colour that we cannot see. Plants often use ultraviolet markings to attract insects to their flowers. These markings are called nectar guides. They steer insects towards the centre of a flower, so that they can collect a meal of nectar, and carry pollen from one flower to the next.

EARS AND ANTENNAE
Many insects communicate by sound, but their ears are not always on their heads. Crickets have their ears on their legs, while grasshoppers and moths have them on the sides of their abdomens. Moths use their ears as an early warning system, to listen out for flying bats. An insect’s antennae (feelers) are multipurpose sense organs. They can smell, touch, and taste, and they can also pick up vibrations in the air.