Summer is the time to see insects on the wing. But how do these diverse and myriad creatures take flight?
By LEV PARIKIAN
T here is, according to author Douglas Adams, a knack to flying: throw yourself at the ground and miss. Humans are terrible at flying. We are too big, too heavy, too wingless. Insects, though, thrive in the air, and developing the ability to fly has played a large part in their success.
With wings you can escape a predator; move to more advantageous habitats; radiate, diversify and take over the world. The first insect flew at least 325 million years ago, and it quickly caught on. Like the Duke of York’s men, once they were up they were up – and for them there was no coming down.
Insect flight manifests itself in many different ways, whether it’s the breathtaking control of a dragonfly, the exasperating agility of a house fly, the winsome scattering of a cabbage white, the dogged whirring of a stag beetle or the clumsy bumblings of a daddy longlegs.
The principle is simple: four forces – lift, thrust, weight and drag – act on a flying body. Produce enough lift and thrust to counteract the weight and drag, and up you go. Yet the reality is more complex. The conundrum facing any flyer is to combine lightness with strength. Insects solve this by making their wings from the same stuff predominant in their exoskeletons: chitin. The typical insect wing is a sandwich of this highly effective, lightweight material: two layers squeezed together and interlaced with a network of veins, which serve the dual purpose of strengthening the wing and circulating blood (haemolymph in insects).
So that’s the lightness and strength taken care of. But to get (and stay) in the air you need a form of propulsion and, as an insect wing contains no muscle, that must come from the body. Insects have evolved two solutions for this. The simpler version is the direct flight mechanism, which is utilised by two orders: Ephemeroptera (mayflies) and Odonata (dragonflies and damselflies), as well as some cockroaches. In direct flight, muscles act directly on the wings: muscle down, wing up and vice versa. An individual needs two sets: depressors for the downstroke and elevators for the upstroke. It’s a pleasingly simple arrangement, and it works well, even if wingbeat speed tops out at about 200 beats per second (fast, yes, but it can be much faster – read on), limited by the connection of the muscle contractions to the speed of nerve impulses.
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