Mosquitoes May Fly Well In The Rain, But They Fail In The Fog

Lee Rannals for — Your Universe Online

Researchers have determined that despite their amazing ability to fly in the rain, mosquitoes fail miserably while trying to fly in heavy fog.

Scientists reported at the 65th meeting of the American Physical Society’s (APS) Division of Fluid Dynamics that just like airplanes, the blood-sucking insects are grounded when fog thickens.

“Raindrop and fog impacts affect mosquitoes quite differently,” Georgia Tech researcher Andrew Dickerson said in a statement. “From a mosquito’s perspective, a falling raindrop is like us being struck by a small car. A fog particle — weighing 20 million times less than a mosquito — is like being struck by a crumb. Thus, fog is to a mosquito as rain is to a human.”

Mosquitos get struck by a drop once every 20 seconds during a rainstorm on average, and still manage to stay afloat. However, a cloud of fog presents a different scenario.

Water droplets in a fog cloud are so small they do not weigh down a mosquito enough to affect its ability to fly, regardless of their abundance. So, the team decided to determine why the flying insects are so affected by the haze. The researchers looked to high-speed videography for a little help in making that determination.

They found that mosquitoes have reduced wing-beat frequency in heavy fog, but retain the ability to generate sufficient force to lift their bodies, even after significant dew deposition. However, they are unable to maintain an upright position required for sustainable flight.

Fog impacts a mosquito’s halteres, which are the insect’s primary flight control mechanism. Halteres are small knobbed structures that evolved from the hind wings and flap anti-phase with the wings, providing gyroscopic feedback through Coriolis forces.

These halteres are a comparable size to the fog droplets, and they flap about 400 times each second, striking thousands of drops per second. Although they can normally repel water, repeated collisions with 5-micron fog particles hinder flight control and leads to flight failure, according to the research.

“Thus the halteres cannot sense their position correctly and malfunction, similarly to how windshield wipers fail to work well when the rain is very heavy or if there is snow on the windshield,” Dickerson commented. “This study shows us that insect flight is similar to human flight in aircraft in that flight is not possible when the insects cannot sense their surroundings.”

He said that for humans, visibly hinders flight, but for insects it is their gyroscopic flight sensors that suffer.