Flying in the Rain

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Dr. William V. Raszka, our Associate Editor, offers the following insight into a current topic in the news:

I was working in the garden on a hot, humid evening recently and became irritated that I was being bitten by so many mosquitoes. I could see a squall line approaching from the west and thought that the rain would limit the mosquito’s ability to fly. Much to my chagrin, the mosquitoes seemed undeterred by the deluge and continued feasting. How could this happen? After all, the weight of a raindrop is more than 50 times that of a mosquito. I would think that mosquitos would be crushed—think of a 3-ton drop of rain falling on us at 20 miles per hour—during a rainfall.

According to an interesting segment from NPR (Morning Edition: June 5, 2012), the mosquito, by nature of its small size and strong exoskeleton, is superbly adapted to flight in rain. Researchers studied the effects of rain drops on mosquitoes in a controlled environment. They found that mosquitos make no attempt to dodge the raindrops but simply roll with the punches. Drops that hit the wings or legs caused the mosquito to skew or tilt its flight. However, after a brief pause, the mosquito is able to continue flying.

A raindrop landing between the wings of the mosquito, at the center of its mass, had a very different effect. The mosquito and raindrop merged—that is, rather than resist the raindrop, both the drop and mosquito fall together for a brief period. After a fall of approximately 13 body lengths, or a thousandth of a second, the mosquito’s wings catch the air and the insect is lifted, unharmed, from the drop. The major risk for a mosquito is flying low or close to a solid object and not having enough time to escape from the drop. The results have several implications (beyond my knowing why I was still getting bit despite the rain). Engineers of very small robots can use this knowledge to design their robots. Secondly, swatting a mosquito against a hard surface is likely to be more effective than trying to swat one midair.

Noted by WVR, MD

*This filler excerpt can be found in the September 2012 Pediatrics print journal p. 521, or via online here.