In a small, blackened, window-less room, somewhere in the labyrinth of the zoology department, there is a movie set. A spotlight picks out the actress. Baby oil pours down a heated wire, creating smoke which, carried by the wind from a concealed fan, blows over her.
A high-speed camera records her every move.
The actress is an insect, a butterfly and she flaps her wings vainly for the wind is strong. She cannot escape the camera’s gaze. Her every move is monitored, recorded and scrutinised by men thirsty for pure knowledge.
Adrian Thomas, Bob Srygley, Graham Taylor, Robert Nudds and Richard Bomphrey make up the research group at the Zoology department looking at the question of how insects fly. When I first interview them, Adrian is in the skies above the Sierra Nevada, Southern Spain, testing his science on himself. Bob refuses to talk to me on the grounds that his novel findings are just about to break in Nature. Graham, Robert and Richard collect in an office and take me back to first principles.
According to aerodynamic laws derived by engineers, insects can’t fly. The bumble bee is the example everyone has on the tips of their tongue on a summer day, (like ice cream). Bumble bees can’t fly. Application of the classical Bernoulli principle implies that a bee is too heavy relative to its wing size to fly, and so for that matter is every other insect. Flight depends on getting yourself off the ground. Upwards lift is produced when a wing shaped object moves forwards through air, and the air splits at the leading edge. The air moving over the top of the wing has further to go than the air moving underneath. This means the air above travels faster, and is therefore at lower pressure. Higher pressure underneath the wing produces upwards lift.
Animal flight has traditionally been studied, as though at each instant in the flapping cycle, the wing were behaving like the wing of an aircraft, flying steadily through air. This mode of research, suggests that insects cannot fly, as the upwards forces are insufficient to keep them in the air. Trying intently to follow this engineering algebraic logic, I am semi-convinced until Robert gently reminds me that insects do in fact fly. What their science does is try to bridge the gap between theory and fact.
Insect wings move in very mysterious ways. They not only move up and down, but rotate as they do so, and in some insects elegantly bend down at the edges, like a cloak wrapping around their bodies. Robert and Graham are now on their feet flapping their arms to demonstrate. It is not very easy to watch an insect flying – on the next sunny day try it! This is where that movies set comes into its own. The video camera is high speed and digital, paid for by the BBSRC. Television cameras take an image 25 times a second, which is about as often as a locust flaps its wings. Their high speed camera takes a snapshot 500 times a second, so every time the locust flaps, 20 images are generated, clearly revealing what the wings are doing. The baby-oil- smoke shows the researchers how the air around the wings reacts. The results look stunning on the monitor. A phantasmagorical creature, bathed in light creating swirling vortices in the visible air.
The research focuses on two problems: How do animals produce lift; and how do they remain stable? Previous research has been conducted on tethered insects, but Adrian describes this as “flapping on a stick”, which may not reflect the true nature of insect flight. Bob’s research breaks ground in looking at free flying insects. The insects have to be slow fliers though, hoverflies, dragonflies and butterflies. Fast insects are no sooner there than gone – no research possible on a data point that vanishes. Humming bird hawkmoths are a new recruit. These can be persuaded to follow a nectar feeder, made from a golf tee around the room.
Richard and Graham use insects which are tethered, so they can work with fast flying locusts which can travel 3.5 meters per second, 12 kilometres an hour. They also work with minute machinery, “any engineer will know what I am talking about”, says Graham, so I keep quiet and listen. A force balance is a tiny piece of milled metal, capable of measuring forces which arise as the metal bends in a certain direction. Data are collected on a remote computer. The insects sit on the force balance, stuck with superglue (after the experiment they can be detached and released). Air moving around the insect can be observed simultaneous to the generation of a force.
This is a poetic science. A gnat’s wing moving in air, I am told, is like a cricket bat paddling its way through treacle. Flying is like swimming, you do a forward stroke and then a recovery stroke. Unless the forward stroke exceeds the backstroke in power, you stay still. When we walk, the foot as it moves backwards is off the ground. But air is all around you, like water in a pool, so you cannot help but to act on the substrate when you move in any direction. The key is to minimise the power with which you move in the wrong direction.
As well as staying up, insects have to stay upright in the air. Throughout the history of aviation, there has always been a problem of stability. Early aircraft fell out of the sky because they couldn’t keep themselves facing in the right direction at the right angle to the ground. Graham spends a lot of time thinking about the maths of this problem for a flying animal. He also plays with small cardboard tubes. He brandishes it in front of me saying that if you drop it, nose downwards it will tumble rather than fall straight. I argue with him – “shouldn’t it fall nose down?” Yes, says Graham but there are always forces acting on it, turning the tube, flipping it. “In a vacuum”, I argue, “wouldn’t it fall straight down in a vacuum”. “Yes”, says Graham, “but the world is not a vacuum, in fact it’s a very turbulent world”. A philosophical science too.
Then, “Darts” says Graham, unprovoked, “are like mayflies”. Here the cardboard tube has its encore. He throws it across the room and at the end it flips forward and crashes. Then he attaches two pieces of red cotton to its tail end and throws it again. Result. The tube flies smoothly and at least crashes with all its passengers upright. Mayflies also solved this problem by evolving cerci, streamers at their tail end. One of Graham’s mathematically deduced insights relates to flapping. “Flapping doesn’t destabilise you” says Graham, matter-of-factly. “Speak for yourself”, I say – “not if you’re an insect” says Graham. What flapping does for an insect is amplify the existing physical stability.
I am persuaded that the study of insect flight is dramatic, poetic and complex. I still don’t understand exactly what the wind tunnel has contributed to the science of flight. Finally, after 8 weeks in the sky, Adrian, Britain’s number one paraglider is back. I meet him in Café Coco on the Cowley Road. Adrian is obsessed with flight. “As a kid I would fly a kite”, he tells me, “and wish that it would pick me up off the ground and take me with it”.
So why can insects fly? The wind tunnel has revealed clever ways insects have of exploiting air. Insect flapping produces a spinning mass of air above the wing which means that the air has to travel further, creating more lift. It is as though the insect has a larger leading edge to the wing because it carries a rotating cylinder of air over which the oncoming air has to pass, but it creates this effect without having to carry any extra body weight.
Another feature of insect flight is “clap and fling”. When the insect flings its wings apart, after clapping them together at the top of the wing beat, it creates extra lift by drawing additional air into the flow. “Wake capture” enables the insect to increase lift by passing the wing through the vortex created by the previous stroke. Another revelation is that forces are generated in two directions with the upstroke: forwards and upwards and that the wings of an individual insect do different things from one stroke to the next. When a butterfly flutters it is not just going fast then slow, then fast, it behaves as if we were to run, walk, run, walk in quick succession, using different modes of locomotion on each wing beat. The insect is creating very different vortices with these different types of locomotion. A butterfly flapping is disconcerting to watch, and interestingly, aposematic (bright, nasty-tasting) insects don’t flutter, perhaps because they have alternative ways of defending themselves. Adrian suspects insects may be using their flight patterns to confuse predators.
This science has a deadly side. The most likely applications of this work are military ones. Imagine small, intelligent flying machines which can move inside buildings, turning corners, carrying weight greater than seems reasonable, bearing video cameras or even bombs. In California scientists have built small machines which can fly for a few seconds. But none of them want to go into that, verbally or actually. Their work is a pure passion. Bob is looking forward to his Nature papers, Graham wants to take his understanding of maths into ecology and Robert wants to work with some real animals instead of his model insects. Adrian will keep on talking about flying, thinking about flying, working on flying, flying – no fear.