The muscles that help a bluebottle fly to perform incredible aerial acrobatics have been revealed in 3D real-life videos for the first time.

The Calliphora vicina fly, or bluebottle, is one of nature’s most complex flying machines. Its flight is controlled by ‘power’ muscles, which give the fly lift, and ‘steering’ muscles, which help the fly to manoeuvre. These muscles enable the creature to perform highly complex manoeuvres, even in the face of unpredictable wind turbulence.  However, scientists have previously not been able to properly visualise these sets of muscles in action.

Now, researchers have developed a technique for ‘filming’ inside flies while they are beating their wings, using CT scanning technology. The team have reconstructed the power and steering muscles in flight in three dimensions, giving insights into how a fly performs aerial feats.

Click on the video above to see the muscles in action.

The researchers say their technique could be used to learn more about how muscles enable other insects to move around. Their results could also inform the design of new micromechanical devices and miniature unmanned aerial vehicles, which attempt to mimic flies’ aerial skills.

The study, published today in the journal PLoS Biology, was carried out by researchers from Imperial College London, University of Oxford, and the Paul Scherrer Institute.

Dr Holger Krapp, Reader in Systems Neuroscience in the Department of Bioengineering at Imperial, says: “Before you next think about swatting a fly, take some time to marvel at its incredible aerial acrobatics. In the time it takes a human to blink, a blue bottle has flapped its four wings 50 times and manoeuvred them at different angles to fly out of range to avoid your swats. We are excited because for the first time, we can properly visualise how these muscles work in real-time, providing us with insights into the tiny mechanisms that make these flies so masterful in the air.”

The videos are providing new information about how the power muscles in the fly’s middle body segment, called thorax, help these flies move through the air. One set of power muscles connects the front and the rear ends of the fly’s thorax and another one runs from the top to the bottom of the thorax. The contraction of each set of power muscles causes the thorax to compress and expand. The energy from this movement is transferred via ‘hinges’ on the thorax to the wings to give the fly its lift and power. This process enables the insect to keep a straight flight trajectory.

The team were also able to visualise tiny ‘steering’ muscles, which are hidden inside the thorax. These manipulate the amplitude and orientation of each individual wing, determining how much lift is produced as the fly moves through the air. Slightly different activation of the steering muscles on either wing enables the fly to perform turning manoeuvres. The researchers also discovered that some of the steering muscles can be used like a gearbox in a car, where shifting to a lower gear can slow it down.

To obtain the 3D models of these muscles the team went to the Swiss Light Source, near Zurich, and used their synchrotron facilities. Synchrotrons enable the generation of X-ray radiation that penetrates tissue that would otherwise block visible light.

The fly was secured to a device that enabled them to turn it around so that they could make images or radiographs of the power muscles from multiple angles and at multiple stages of the wing beat.

In a reflexive response to counteract the rotation, the flies attempted to turn in the opposite direction during the scanning process. This enabled the scientists to record the movements of the steering muscles inside the fly. The resulting radiographs were then combined to make 3D visualisations of the power and steering flight muscles as the fly’s wings oscillated back and forth 150 times per second.

The next phase of the research will see the team further developing their technique so that they can simultaneously carry out x-ray scanning of muscle movements and take measurements of parts of the fly’s brain responsible for controlling these muscles. The ultimate goal is to apply what they learn to new generations of autonomous robots and assistive systems.

Dr Krapp adds: “Evolution has had hundreds of millions of years to overcome many of the problems that creatures like insects face. It is certainly worthwhile identifying the solutions nature has come up with and exploiting them in a way that benefits many areas of human life, where autonomous robotics will pay an increasingly significant role in the future.”

The research was also carried out by Dr Martina Wicklein, from the Department of Bioengineering, and Imperial alumnus Daniel Schwyn.

Dr Martina Wicklein, along with Imperial alumnus Daniel Schwyn, has also developed a video (below) that takes us on a journey through a fly’s innards. Dr Wicklein, who is part of Dr Krapp’s research team, narrates during the journey.

The fly

bioengineering