How mosquitoes fly, even though they shouldn’t be able to

Mosquitoes’ tiny wings shouldn’t be able to lift their bodies. Now, researchers have figured out how they get off the ground.

Most people are all too familiar with the distinctive buzzing sound of mosquitoes in flight. Yet, it’s a wonder that mosquitoes can fly at all. They have long, thin wings that would not be able to lift their weight using only mechanisms other insects use to fly. Now, new research reveals the aerodynamics that keep mosquitoes aloft. We spoke with one of the study’s authors, biomechanics expert Richard Bomphrey, to learn more.

ResearchGate: What motivated this study?  

Richard Bomphrey: From a societal perspective, mosquitoes are hugely important, having an enormous impact on human and animal health. The mosquitoes we studied are vectors for avian malaria, roundworms causing lymphatic filariasis, and various encephalitic viruses, possibly including Zika.

From a biomechanical perspective, mosquitoes are very interesting because their wing beat frequencies are so much higher than other insects of the same size. This is curious because the impact of increasing frequency is very expensive energetically. In fact, if you double the frequency, the power needed for flight increases eight-fold.

RG: Can you tell us what you found?

Bomphrey: We found that the wing beat pattern of mosquitoes is very unusual. They sweep their wings through an angle of just 44 degrees on average, less than half that of the next nearest insect we have studied in depth, the honeybee.  This is in stark contrast to the continually sweeping wings of a helicopter, or the long-distance gliding wings of airplanes. Lift does not build up in the same way, and the standard theories of aerodynamics start to fail. So we knew something odd was occurring! Mosquitoes had to be doing something else to generate the lift required for flight. We discovered much of the lift force they generate comes during the rapid changes in direction at the upstroke-downstroke transitions.

RG: How did you come to this conclusion?

Bomphrey: During these fast wing rotations, we calculated extra forces that were not predicted by existing models. These matched with two aerodynamic mechanisms that had not been observed before. One is lift through rotational drag, caused by the rotations of the wing itself. The other is a phenomenon called the trailing-edge vortex, meaning the wings recoup some of the energy that would otherwise be lost to the environment.

RG: Why did we not understand mosquito flight until now?

Bomphrey: Have you ever tried taking a picture of an insect in flight? It's hard! Mosquitoes are small and beat their wings incredibly fast. We needed to use eight state-of-the-art, synchronized, high-speed cameras recording at 10,000 frames per second to capture sufficient detail of the wing motions. The camera views were used to reconstruct the body and wing surfaces in 3D, but this was just the beginning.

We then used those data for comprehensive computational fluid dynamics simulations to reveal air flow velocities. These results were validated using a powerful laser to illuminate a mist of particles in a fog around the mosquitoes. It was a complex process but, happily, our experimental and simulated results matched very nicely and we could be confident about our conclusions.

RG: Why do you think they evolved this way? Does this way of flight give mosquitoes an advantage?

Bomphrey: I don't think we can say that these new mechanisms of generating lift give mosquitoes an advantage. We know they must already be at the limit of performance because of the power costs associated with the high frequencies. My hunch is that they are invoking the trailing-edge vortex because otherwise flight may not be possible at all. This leaves the question open as to why natural selection has pushed mosquitoes towards such high frequencies. Biology is always a compromise, and it could be that this is nothing to do with flight per se, but instead acoustic communication or some entirely different reason.

RG: What is the significance of your results?

Bomphrey: This is the first new mechanism found in insects for over twenty years. It is quite surprising that we knew so much about aviation and even supersonic flight, yet so little about mosquitoes, especially considering their impact on farming and human health. Applications could be in novel acoustic traps or engineered devices. Again, when we engineer flying machines, we can make them very fast indeed, but have yet to manufacture anything at small scale that can hover for a reasonable length of time. Taking inspiration from a group of animals that has been airborne for over 350 million years seems a sensible idea!

Featured image courtesy of Wellcome Images