In termites and ants, which are social insects, there are wingless forms and winged reproductive forms. The winged forms have large wings that are shed immediately after the nuptial flight. Some insects have become secondarily flightless and have wings that are very reduced. Two groups of insects, the silverfish and the bristletails, diverged from the rest before the evolution of flight and have never had wings, but all the fleas and lice had wings at one time and have now lost them.

Wings are sometimes preserved in the fossil record and there are particularly fine specimens of dragonfly from the Carboniferous coal deposits. The fossil dragonflies appear very similar to present day forms, except that some species were giants. The largest species of the fossil genus Meganeura had a wing span of about one metre, ten times larger than the span of the largest dragonfly that exists now. All the evidence from the fossils suggests that Meganeura was a fast-flying predator like modern dragonflies. Imagine what it would be like to meet a dragonfly of that size – even our present day dragonflies are very impressive!

In gliding flight, the airflow over the outstretched wings is sufficient to provide lift that counteracts the forces of gravity and drag. The leading edge of each wing must meet the airflow with a positive angle, called the angle of attack. This angle can be as much as 50^o, which is much more than the maximum of 20^o that an aircraft wing can sustain without stalling.

Most insects are too small to make use of gliding flight and fly by beating their wings. The rate at which the wings beat shows large variations between species. For example, large butterflies have a wing beat frequency of around five hertz whereas some midges beat their wings almost 1000 times each second.

Insect	Wing beats per second	Flight speed/km h-1
Large dragonfly	22 to 28	25.2
Mosquitoes	275 to 575	3.2
House fly	190 to 330	6.4
Honey bees	190 to 250	22.4
Desert locust	18 to 24	16.0

The development of high speed photography helped greatly in the study of insect flight, but getting an insect to fly when a film camera was running at very high speed was very difficult – and think of the cost of the film! Some studies were made using stroboscopic light, where light flashes were synchronised with wing movements to make the wings appear stationary.

But now, high speed video lets us record insect flight more easily and, using disc drives, we can record continuously. So, instead of waiting for the insect to take off and then start the camera (and how can you predict when take-off will happen?), we can leave the camera running until it takes off and then stop the camera afterwards, knowing that we have the complete take-off stored.

There is a fascination in the study of insect flight and the senses associated with it. The interest comes partly from the wide range of subject areas that contribute to the analysis of flight, from biochemistry through to physics, but also the sheer beauty of insect wings and their staggering variety. Flight is an evolutionary development that has led to the unique diversity of insects and their central role in most terrestrial habitats.

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