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June 6, 2012

Bad news: Raindrops don't swat down mosquitoes

Findings could aid design of tiny flying robots

(Continued)

The experiments showed that the water drops, which ranged between one and 300 times the weight of the mimics, slowed only 2 percent to 17 percent upon impact. The team concluded that the raindrops deform and largely bypass the much smaller bodies of the mosquitoes. Hu and his co-authors suggest in their report, published online this week in the Proceedings of the National Academy of Sciences, that this surprising effect is due not only to the mosquito's lightness of being but also to its exoskeleton, the hard outer covering that protects its inner organs.

To corroborate their findings, the team subjected the mosquitoes to one last stress test, compressing the insects' bodies to reveal what forces they could actually withstand. The team had calculated that the impact of a raindrop amounted to between 200 and 600 dyne, a standard measure of applied force. After being subjected to a compression of about 3000 to 4000 dyne, many times the impact of a raindrop, the mosquitoes were still able to fly once released.

Robert Dudley, an expert on insect flight at the University of California, Berkeley, says that the paper "convincingly shows that mosquitoes survive and mechanically compensate for single impacts of relatively large water drops mostly because of their low mass as well as their flexible . . . exoskeleton." Voigt adds that the study is a "wonderful contribution" to our understanding of how flying animals perform under various weather conditions. Voigt says that he was "really struck, like the mosquitoes" by the very high G forces, up to 300 times gravity, that the insects are subject to, which is the "highest ever recorded acceleration that animals have survived." (Humans can withstand only about 25 G.)

Hu says that his team's results may have implications for the design of so-called micro-airborne vehicles (MAVs), some of which are as small as dragonflies and are increasingly used by the military for surveillance in war zones and for search-and-rescue operations. Voigt, however, is skeptical. "We are far away from creating aerial robots the size of a mosquito," he says, "I am unsure whether these findings may be incorporated" into superior MAV designs.

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