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Raindrops no match for low-mass mosquitos

posted 5 Jun 2012, 07:53 by Mpelembe   [ updated 5 Jun 2012, 07:54 ]

As both a disease vector and general nuisance, the mosquito is a scourge all over the world. Its resistance to the effects of sprays and pesticides is widely known but now scientists have revealed just how tough the blood-sucking insect can be.

A single raindrop can weigh 50 times more than a mosquito, yet the insect can fly easily through a downpour.
Using high-speed videography to determine how they do it, researchers at Georgia Tech in Atlanta found the mosquitos' strong exoskeleton and low mass render it impervious to falling raindrops.

The research team, led by Assistant Professor of Mechanical Engineering David Hu and his doctoral student Andrew Dickerson, found that mosquitoes receive low impact forces from raindrops because the mass of mosquitoes makes virtually no difference to the momentum of the drops.

The results of the research appeared in the June 4 issue of the Proceedings of the National Academy of Sciences.

"The most surprising part of this project was seeing the robustness this small flyer has in the rain," Dickerson said. "If you were to scale up the impact to human size, we would not survive. It would be like standing in the road and getting hit by a car."

The scientists say their findings could be used to enhance the design and features of micro-airborne vehicles, which are increasingly being used by law enforcement and the military in surveillance and search-and-rescue operations.

To study how mosquitoes fly in the rain, the research team constructed a flight arena consisting of a small acrylic cage covered with mesh to contain the mosquitoes but permit entry of water drops. They used a water jet to simulate rain stream velocity and observed six mosquitoes flying into the stream. All the mosquitoes survived the collision.

"The collision force must equal the resistance applied by the insect," Hu said. "Mosquitoes don't resist at all, but simply go with the flow."

The team also filmed free-flying mosquitoes that were subjected to rain drops. They found that upon impact the mosquito is adhered to the front of the drop for up to 20 body lengths.

"To survive, the mosquito must eventually separate from the front of the drop," Hu said. "The mosquito accomplishes this by using its long legs and wings, whose drag forces act to rotate the mosquito off the point of contact. This is necessary, otherwise the mosquito will be thrown into the ground at the speed of a falling raindrop."