Mosquitoes in the Rain
The
mosquitoes are tiny and annoying flying insects that plague many lands
particularly during the summer. Although a few species are harmless or even
useful to humanity, most are a nuisance because they suck blood from
vertebrates, many of them attacking humans.
In
feeding on blood, various species of mosquitoes transmit some of the most
harmful human and livestock diseases. Sprays, pesticides, citronella candles,
bug zappers — nothing seems to totally deter the blood-sucking insect.
And
neither can rain apparently. Even though a single raindrop can weigh 50 times
more than a mosquito, the insect is still able to fly through a downpour.
Georgia Tech researchers used high-speed video cameras to determine how this is
possible. They found the mosquito’s strong exoskeleton and low mass render it
impervious to falling raindrops.
The
research team, led by Assistant Professor of Mechanical Engineering and Biology
David Hu and his doctoral student Andrew Dickerson, found that mosquitoes
receive low impact forces from raindrops because the mass of mosquitoes causes
raindrops to lose little momentum upon impact. The results of the research will
appear in the June 4 issue of the Proceedings of the National Academy of
Sciences of the United
States of America .
"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."
What the
researchers learned about mosquito flight 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 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."
So the
mosquitoes escape the massive raindrop by eventually climbing over or out of
it.
