Science Square

  • Issue 88 / July - August 2012

    What do mosquitoes do when it’s raining?

    The Fountain

    What do mosquitoes do when it's raining?
    Mosquitoes like climates with high humidity and rainfall. While a single raindrop can weigh 50 times as much as a mosquito, how can mosquitos fly and survive under what seems to be a devastating weather condition for them? Andrew Dickerson and co-workers at Georgia Institute of Technology examined the effects of falling raindrops on the flying mosquitoes using high-speed video capture and found that rain does no damage to flying mosquitoes. Upon impact with mosquitoes, the raindrops do not splash and scatter but they merely deform and hold together. This was calculated to be due to the small diameter and the velocity of the drop. On the other hand, given the relatively small mass of the mosquito, the drop does not significantly alter its speed. A partial hit on the mosquito by the falling drop causes the mosquito to rotate around its flight path. Mosquitoes were found to easily recover and resume their flight immediately after the impact. In the case of a direct hit by a raindrop, the mosquitoes were still able to literally separate themselves from the drop after traveling with the drop for a while without lethal damage and resume flight. The researchers further analyzed the impact force of the raindrops on the mosquitoes and found the direct impact to exert around 80 times the gravitational force. This is an extremely high force for larger organisms however, for mosquitoes with a very strong exoskeleton, this turned out to be a minor fraction of 1500 X g, which the researchers tested the mosquitoes and found them to be still able to fly! The outstanding resilience of such a small organism already inspired scientists to start designing very small robots that may serve as airborne search-and-rescue vehicles. But scientists are still very much limited by the basic factor of how small they can go.

    What exactly happened in AD 774?
    Researchers in Nagoya University of Japan have recently discovered a cosmic mystery when they were analyzing the growth rings of two cedar trees that are as old as 1200 years. All trees are known to incorporate particles from the atmosphere during photosynthesis. Carbon-14 (C14), one of the exceptional elements in the atmosphere, is generally formed by massive solar flares or by supernovae and it is present in very low percentages. Interestingly, researchers found that the cedar tree ring produced during the growth season of AD 774 had about 1.2% more C14 than in the previous years, that is about 20-times more than the usual range of 0.05%. These results indicate that some cosmic event during AD 774 generated a major influx of radiation leading an excessive amount of C14. Only a massive supernova explosion might have been strong enough to create this much radiation. However, if this was a supernova, we should either be able to catch the traces with modern telescopes, or find historic documents reporting this extraordinary cosmic event. But, we simply have no record of anything unusual happening in our skies in that period. Alternatively, a massive solar flare might have created such a radiation. In fact, 13th-century English chronicler Roger of Wendover mentions a cosmic event that could possibly be a solar flare. However, a flare with that magnitude would have been the biggest solar flare ever recorded by our sun and probably would have destroyed the Earth's protective ozone layer leading to disastrous ecological consequences. Thus, the flare hypothesis seems also unlikely. By now, scientists are only positive that some very energetic event occurred in 774. But what exactly was it? Frankly, their guess is as good as ours.


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