Mosquitoes survive raindrop collisions

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.

8c1ba4_e3cf637ac15e425dbc81c8e2fafbb3c7

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.

8c1ba4_459da78e1df14da884f01a4d410ec2e8In 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!

8c1ba4_03421759cd0644ad91a9cd018ba4df0eMosquitoes 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.

8c1ba4_ab1177852d844ccb8277964635bd3170

8c1ba4_3dfb4375d03a488f872eecbdaeace37f

8c1ba4_7d974ed3b97648ae8e355231269aef39

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

METHODS

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.

8c1ba4_9373ef67424d49cabec54141566e9b77

8c1ba4_4606166cad4648c0abe0cf668c9134b2