Synopsis: Fruit flies swim through air

The paddling motion works not just for swimmers but also for fliers, as new high-speed video observations of fruit flies show.
Synopsis figure
Credit: L. Ristroph et al., Phys. Rev. Lett. (2011)

The fruit fly buzzing around your fruit bowl may be doing the butterfly stroke. A new experiment reported in Physical Review Letters shows that—contrary to popular wisdom—paddling can be as effective in air as it is in water. This could imply that insects evolved their flight capability from some earlier swimming trait.

Flying is typically associated with the force of lift that results from the pressure difference above and below a wing. Birds and other fliers generate lift during a flap by tilting their wings so as to slice through the air. Although some swimmers also use lift to move through water, the more common force is drag. Drag is the resistance from the surrounding fluid, but it can also be used for propulsion, as when the swimmer Michael Phelps “pulls” water with his cupped hands.

Drag-based paddling was thought to be confined to swimming, but recently it was observed in the hovering of dragonflies. Leif Ristroph of Cornell University and his colleagues wanted to test whether drag could also produce forward flight. Their chosen subject was the common fruit fly (Drosophila melanogaster). Using high-speed video cameras to track wing motion, the team observed certain cases where the flies paddled their wings forward and backward. To confirm that this was indeed drag-based motion, the team plugged their wing data into an “insect flight simulator” and found that they could reproduce the fly’s overall movement. The authors constructed a simple model of paddling, which seems to support the theory that insect wings evolved in water. – Michael Schirber


More Features »


More Announcements »

Subject Areas

Fluid DynamicsInterdisciplinary Physics

Previous Synopsis

Quantum Information

Preventive circuitry

Read More »

Next Synopsis

Particles and Fields

Binding baryons on the lattice

Read More »

Related Articles

Synopsis: How Ice Bridges Form

Synopsis: How Ice Bridges Form

New theoretical work predicts the conditions under which sea ice will clog a narrow channel to create a natural bridge across it. Read More »

Viewpoint: Searching for Order in Turbulent Flow
Fluid Dynamics

Viewpoint: Searching for Order in Turbulent Flow

The observation of ordered flow patterns in a weakly turbulent liquid may lead to new ways of predicting the evolution of turbulent flow. Read More »

Synopsis: Little Spheres Are Pushy
Soft Matter

Synopsis: Little Spheres Are Pushy

A simple diffusion model explains why small particles tend to push big ones to the bottom of a drying colloid film. Read More »

More Articles