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How a mosquito survives in rain: insects ride drops downward then depart before the splat.

A raindrop hitting a mosquito in flight is like a midair collision between a human and a bus. Except the mosquito survives.

New experiments show how the insect's light weight works in its favor, says engineer David Hu of the Georgia Institute of Technology in Atlanta. In essence, the (relatively) huge, fast drop doesn't transfer much of its momentum to a little wisp of an insect. Instead the falling droplet sweeps the insect along on the downward plunge. As Hu puts it, the mosquito "just rides the drop."

The trick is breaking away from that drop before it and the insect splash onto the ground. Mosquitoes that separate themselves in time easily survive a raindrop strike, Hu and his colleagues report June 19 in the Proceedings of the National Academy of Sciences.

Such studies help reveal how animals evolved to take advantage of flight, says biologist Tyson Hedrick of the University of North Carolina at Chapel Hill. Mosquito tricks may also inspire engineers designing swarms of tiny flying robots, or be of interest to physicists studying complex fluid dynamics at this scale.

Plenty of lab work has investigated how flying animals recover from disturbances.

But there's little work on raindrops, as those collisions are hard to study. To mimic a raindrop speed of about 9 meters per second, Hu and colleagues tried dripping water off the third floor of a building toward ground-level mosquitoes. "It's the worst game of darts you can imagine," he says. "You have no hope of hitting them."

Finally, Hu sprayed streams of water from a pump at caged lab mosquitoes and then refined the process by spraying mosquito-sized beads. His team found that mosquitoes hit with water survived using an insect version of tai chi: Move with the blow instead of resisting it. A raindrop can reach 50 times the mass of a mosquito, and after the collision, "the mosquito becomes a stowaway," Hu says.

The wild ride comes with danger. Mosquitoes hitchhiking on water experience acceleration up to 300 times the force of Earth's gravity, the researchers found. The previous champs for surviving acceleration had been jumping fleas, at a mere 135 times Earth's gravity.


Mosquitoes' small mass might allow them to fly through raindrops but leave them more vulnerable to other menaces, such as wind. Larger and heavier horseflies "should have no problem with wind but might be more disturbed by raindrop impacts," Hedrick says.

Scientists who work outdoors know how readily mosquitoes can survive wet weather. "I've worked in the field many rainy nights," says entomologist Nathan Burkett-Cadena of the University of South Florida in Tampa, "and received zero respite from mosquitoes during even heavy rains."

300 g

Top acceleration of mosquito riding a falling raindrop

135 g

Acceleration reached by jumping fleas
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Author:Millus, Susan
Publication:Science News
Geographic Code:1USA
Date:Jul 14, 2012
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