



Video: How mosquitoes fly in the rain

I can stand the rain (Image: Ian Cuming/Science Photo Library)

This is one flyweight battle that promises not to be a washout: the mosquito versus the raindrop. The two combatants might be of roughly equal size, but the raindrop weighs in 50 times as heavy. Why then, wondered David Hu, a mechanical engineer at Georgia Institute of Technology in Atlanta, do mosquitoes flourish in humid conditions where downpours are common?

To find out how – or if – mosquitoes can fly in the rain, Hu’s team used high-speed cameras to film the insects flying through a specially constructed “rain box” – a small acrylic container with a mesh roof. Spraying the roof with water simulated a shower, although the water droplets didn’t fall as fast as normal raindrops.


Hu’s team were able to puncture one urban myth: that mosquitoes caught in a shower somehow dodge the drops. “They showed absolutely no sign of trying to avoid them,” says Hu.

Instead, the footage showed the mosquitoes receive glancing blows and direct hits from the water droplets – each of which knocked the insect off course only momentarily before it stabilised.

Mozzie mimics

Next, the team pummelled Styrofoam pellets with the simulated raindrops to calculate how mozzies can stand the rain. The pellets were filled with a variety of liquids to act as mosquito mimics of realistic sizes and masses. Fast-falling droplets hitting these pellets made a good approximation of a raindrop colliding with a mosquito.

Analysis of the impact showed that when the drops hit an object of low inertia, the droplets deformed but didn’t splash – as a result, little momentum was transferred from the water to the “insect”. Hu calculated that a raindrop would lose as little as 2 per cent of its velocity after hitting a mosquito, and the effect of that would not be enough to disrupt the flight of the insect.

A big win for the bloodsuckers, but Hu thinks the work will be most use in the design of micro-sized remote-controlled aircraft. It will be some years before these micro UAVs are as small as mosquitoes, says Andrew Conn, a bio-inspired robotics researcher at the University of Bristol, UK. But this study highlights such craft “will only be capable of operating in the rain if they have a mass several times smaller, or several times larger, than a raindrop”, he says.

Reference: arxiv.org/abs/1110.3051