Why study mosquito flight in the rain? Mosquitoes are a long-time pest and malaria transmission vector. The more we know about how weather affects them, the more prepared we are for combat.
An understanding of why mosquitoes are able to fly in the rain benefits the design of micro-aerial vehicles, or insect-sized flying robots.
How do mosquitoes survive raindrop impacts? Raindrops can be 50 times more massive than mosquitoes and travel at 10 times the speed (20 mph). This raindrop speed is equal to 1000 mosquito body-lengths per second.
In our study we found that a mosquito’s strong exoskeleton and low mass renders it impervious to falling drops. A raindrop cannot impart a large force on such a lightweight object. Try killing a flying mosquito with your hand!
Mosquitoes do not collide with raindrops as often as you may think. According to our calculations, even in the heaviest ‘cats and dogs’ rain, a mosquito will be hit by a raindrop every 25 seconds on average.
An early attempt at mosquito-raindrop collision.
Drops roll off mosquito wings, unable to wet the insect
Drops roll off mosquito legs, unable to wet the insect.
A video compilation including experimental footage and comments
How do study raindrop impacts on small free-bodies such as mosquitoes? We can view low speed impacts relatively easy by placing a dropper in the mosquito container, filming with a high-speed camera and waiting. Terminal velocity impacts required a pulsatile jets. We tried dropping drops from a height of 10 m (33 ft) with little success.
Once we find that mosquitoes can survive raindrop impacts, and that drops do not splash on mosquitoes, we can lower the drop speeds for experimental ease.
Insect mimics allow for more controlled impacts and filming. By tracking mimics, of similar size and weight to mosquitoes, we can estimate the forces felt by a mosquitoes upon impact.
Our mimic was a small styrofoam bead of the same mass as a mosquito. An important part of the mimicry was suspending the bead in mid-air so it could be struck. The resulting dynamics of impact we found was very similar to the mosquito and allowed us to determine the importance of the mosquito’s mass. Mosquitoes experience more that 300 gravities upon impact, far more than what is survivable by humans.