Skeeters ride the rain

You may barely notice when a raindrop lands on your head. But if you were a mosquito, you’d definitely notice: It would be like a bus falling onto you in midair.

But a falling raindrop doesn’t spell doom for the plucky mosquito, say scientists behind a new study. The pesky bloodsucker might get tossed, rocked and rolled, but its strong body and small size help it survive such collisions. And when a raindrop lands directly on the bug’s back, the mosquito gets taken on a wild ride.

“The mosquito becomes a stowaway,” David Hu told Science News. Hu, an engineer who led the new study, conducts research on animal motion at the Georgia Institute of Technology in Atlanta. In the past, he has probed the science of a wet dog’s shake and the ability of ants to form a raft when threatened by a flood.

Scientists have many reasons for wanting to understand a mosquito’s moves. Engineers who design insect-sized, flying robots may use the mosquito for inspiration. Physicists can learn more about the laws of nature at the smallest scales. And biologists may learn something about how animals evolved, or changed over many generations, to fly.

To study these bugs, Hu and his colleagues had to find creative ways to spray mosquitoes with water. Dripping water on the flying insects from three floors up didn’t work. “It’s the worst game of darts you can imagine,” Hu told Science News. “You have no hope of hitting them.”

So Hu gave up on darts. He and his colleagues decided they’d have more success by spraying small water droplets on mosquitoes in a cage. This worked, and Hu’s team observed that mosquitoes survived because they can go with the flow. When a drop hit a mosquito’s legs or wings, the bug was knocked off course. But when a drop landed squarely between a mosquito’s wings, the bug hitched a ride straight down. That ride can be dangerous: A mosquito on a raindrop may feel a push 100 to 300 times stronger than the familiar pull of gravity. And a mosquito needs to separate from the raindrop while it’s still in the air, before they both smack into the ground.

Hu’s experiments don’t surprise entomologists, or scientists who study insects. The bugs aren’t scared off by a summer shower.

“I’ve worked in the field many rainy nights,” entomologist Nathan Burkett-Cadena of the University of South Florida in Tampa told Science News, “and received zero respite from mosquitoes during even heavy rains.”