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The first flyers, insects

Insects were the first animals to master flight; nearly 100 million years before (wait for it) the reptiles took to the air (more). And 150 million years before the dinosaurs (birds) did (more).

It’s always a bit of a puzzle how a dramatic development like flight could have happened, through ordinary evolutionary processes – particularly when it all happened so long ago. But there is quite a lot that we can say.

This picture of a mayfly nymph comes from ‘History of Life’ by Richard Cowen. The nymph hails from the early Permian, about 280 million years ago. To be sure, this is not particularly early. It would have been nice to have found such a fossil older than the first insect flyers. But you have to take what you can get in palaeontology. And to find such an exquisitely preserved fossil of any age was a great stroke of luck.

This larva’s ‘wings’ are well developed, and were clearly functional. But they were not for flying, they are far too small for that. They were for rowing through the water. As I understand it, modern mayfly nymphs have the same feature. These wings are modified gills. Insects are the only flyers that didn’t have to sacrifice any limbs for flight.

Now small creatures perceive the air as being much more viscous (treacly) than large creatures do. In aerodynamic parlance, they have a very small Reynolds Number. So the transition from ‘flying’ through the water to flying through the air will not have been as daunting for them.

Some small living water bugs use their wings to fly in water and in air, and they use them in exactly the same way. Compare that with diving birds, who have to partly fold their wings when ‘flying’ underwater.

So, of the different animals that have mastered flight, the insects probably found it the easiest.

The oxygen level was high at the time too, on account of the burgeoning rain forests (more). This will have enabled the insects to work their muscles harder to get into the air. It will have made the atmosphere denser too, which will have given their wings more grip.