Insect Flight

Insects are some of the most impressive fliers in the animal world because of their small size. Dragonflies dart through the air after prey, and bees speed over fields and gardens in search of flowers. Hover flies can stay rock-steady in mid-air, while butterflies can migrate across entire continents. To do all this, insects use special flight muscles that power their wings. These muscles are packed inside an insect’s thorax, and they can work for hours without a rest. Large butterflies flap their wings slowly, so each wingbeat is easy to see. But many insects beat their wings hundreds of times a second, making them vanish in a blur. When wings move this quickly, they make the air vibrate. This creates a buzzing or whining sound.

POWER FOR FLIGHT
Some insects – including dragonflies – have flight muscles that are attached directly to the wings. But in more advanced fliers, such as wasps, they are attached to the thorax. These muscles work by making the thorax change shape. One set pulls vertically, making the top of the thorax move down. When this happens, the wings flick up. Another set pulls horizontally, making the wings drop back down. Once the wings start beating, the muscles carry on automatically until the insect decides to land.

BUTTERFLY IN FLIGHT
This time-lapse sequence shows a butterfly speeding through the air. Beneath it, a time bar shows how long each wingbeat lasts. Butterflies have four wings, but they beat like a single pair. Most of the push comes when the wings flick down, but because the wings twist slightly, some extra push comes when they flick up. In windy weather, butterflies are easily blown about, so they keep close to the ground.

WARMING UP
Insect flight muscles work best when they are warm. When the temperature drops below about 10°C (50°F), many insects are too cold to take off. But not all insects are like this. Bumble bees shiver to warm up their muscles – after a few minutes their flight muscles can be 20°C (68°F) warmer than the air outside. This Arctic bumble bee is feeding on flowers in Greenland, which is less than 750 km (465 miles) from the chilly North Pole.

UNDERCARRIAGE
Many flying insects use their legs to launch themselves into the air. This scorpionfly has taken off with a helpful kick. Scorpionflies are quite weak fliers, so they choose a high point from which to jump. Crickets and grasshoppers give a bigger push – once they are airborne, they can open their wings and fly away. During flight some insects fold their legs away, but many spread them out. This helps them to balance, and also makes it easier to land.

FLIGHT SPEEDS
Insects often fly in short bursts, which makes it difficult to measure their speeds. Many cruise quite slowly, but speed up if they are in danger, or if they are chasing their prey. This chart shows flight speeds for a range of different insects. At 58 km/h (36 mph), dragonflies can overtake most other insects, and even some small birds. However, they cannot keep flying at top speed for long, because their bodies begin to overheat.