By Laurie Noreau – The Rumor Detector
Agence Science-Presse (www.sciencepresse.qc.ca)
Not to upset anyone expecting a reprieve from mosquitoes on rainy summer days, but in fact, these little insects seem to literally slip between raindrops. How? It’s a mystery that interested our Rumor Detector.
You’d think that a mosquito wouldn’t be able to survive the weight of a rainfall. A species that weight barely 2 measly milligrams has to “battle” raindrops that weigh about 100 milligrams. The force of the impact of a raindrop on a mosquito is about equivalent to a human being lying underneath a wheel of a bus. You see why these insects would want to seek shelter when they sense a storm is brewing.
It’s true that most insects avoid flying around on gloomy days. And not just insects: bats stay in, as they have to use twice as much energy as usual to fly through the falling rain.
But the brave little mosquito flies through the heaviest of rains. How does it survive such strong impacts?
If a drop hits its wings or its long legs, it can count on a waxy, waterproof layer to repulse the water by having it slide over. The insect rolls with the drop, and continues its flight in just a few milliseconds. Since 75% of its exposed surface consists of wings and legs, this is what mostly happens.
But if a drop makes a direct impact on its body, which accounts for 25% of its exposed surface, it has to adopt another strategy to avoid being squashed. When the drop hits, the insect lets itself fall towards the ground over a distance equivalent to 20 times its body length to reduce the force it feels. It separates itself from the drop and then continues on its flight. The trajectory is chaotic, but it allows the insect to get from place to place in bad weather.
A consequence of this falling strategy is the acceleration this causes. It’s an acceleration rate that we would call superhuman. When a drop hits the mosquito, the fall has an effect equivalent to a force 300 times that of gravity. That’s what is called the g force.
To compare that with humans, airplane pilots train to tolerate an acceleration equivalent to 9 g (1 g being the normal force we experience when we have both feet on the ground). Being exposed to the same ratio of forces as a mosquito survives would mean certain death for a human being. This rate of acceleration may be the highest survivable acceleration rate in the animal kingdom.
A mosquito’s secret lies in its exoskeleton – like a suit of armor, it is resistant enough to protect its internal organs, allowing it to survive.
As well, a mosquito’s lightness gives it an advantage. Even though a mosquito and a raindrop are about the same size (around 3 mm for the mosquito), the lighter insect will not slow down the raindrop on its route towards the ground. Instead of smashing into the mosquito’s body, the raindrop will change its shape slightly and keep on falling without much of a delay at all.
Paradoxically, being in flight actually helps a mosquito survive rain storms. The mosquito’s fall to absorb the shock, its ability to withstand huge accelerations and its lightness are three ingredients that would not help it at all if it were struck by a raindrop while on the ground. If it were flying too low or not at all, it would be smashed into the ground by the direct impact of a raindrop.