Sunday, July 29, 2012

How Mosquitoes Fly In The Rain

Have you ever wondered how insects, especially small ones like mosquitoes and flies survive the downpour?

Raindrops pose hazard to mosquitoes because of their relatively large mass and speed. A mosquito is around 2~5mm in length, weighs around 2mg, and flies at 1m/s. On the other end, a drop of rain has 1~4mm radius, weighs 2~50 times the weight of a mosquito, and travels at 5~9m/s. Putting that into perspective, it's like us getting hit by a blob of water with the size of a shopping cart, weighs 3 tons and travels at 18~32 km per hour.

It's an irony that the delicate blood-sucking parasite thrives in wet, rain-laden tropical country like Malaysia. Wouldn't they be crushed to death by the raindrops?
Mechanical engineer David Hu of the Georgia Institute of Technology who thought of this question placed some mosquitoes in a cage and exposed them to water drops. Slow motion footage showed that rather than dodging the water drops, the insect flew right into the them.

Since the mosquitoes were so lightweight, the raindrops lost very little momentum upon impact. By minimizing resistance, the insect minimized the impact of collision. So instead of flattening the insect, the water drops simply spun the mosquitoes away, though the insects recovered soon afterward.
It's like an asteroid hitting a piece of paper: the paper is so lightweight that it's just pushed aside.

And nature has given mosquitoes a helping hand: mosquitoes are designed to be hydrophobic, thanks to the hairs on the mosquitoes' body. The hairy surface increases the wing's surface area, and thus its energetic cost of wetting. Thanks to this hydrophobicity, low speed drops simply bounce off the insect.
Moreover, insects are blessed with hard exoskeleton to help them withstand the impact. And mosquitoes could withstand sudden acceleration of up to 300Gs. If we were in a comparable situation we wouldn't even survive past 2Gs.

Thanks to its tiny weight and hydrophobicity, the evil parasite lives to suck another victim.


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