Animals in water: Ants when it rains, Mosquitoes when it rains, the Wet Dog Shake, and Bugs Walking on Water

Have you ever wondered what happens to ants when it rains? Or how bugs can walk on water?

I was extremely privileged to hear from a leading researcher in this field. I attended a seminar at BYU where Dr. David Hu spoke about these topics. Dr. Hu earned his bachelor’s and Master’s degrees in Mechanical Engineering at MIT. He now teaches at Georgia Tech. Specifically, Dr. Hu presented on how water striders walk across water, how fire ants survive in water, how mosquitoes can fly in the rain, and how mammals dry themselves off.


    Dr. Hu showed a video of some water striders doing a mating ritual. The water striders liberally jumped and bounced across the water with ease. He explained that water striders have very hairy legs and stroke the water gently. They are able to stay on top of the water because of surface tension. They are able to move by transferring momentum to the water. In the picture below, you can see in the dye how the eddies trail behind the water strider. The insect is able to transfer its momentum back and forth to the water to push itself forward.

    Fire ants are inherently bad swimmers and water sticks to them easily. They could potentially drown in a rainstorm, but ants have figured out how to overcome it. Ants go into a Cassie-Baxter state, which means they make a water and an air layer. The ants form a 2 level raft and float on top of the water. The ants make artificial gills for themselves and trap pockets of air for them to breathe from. Dr. Hu performed an experiment with 10,000 ants to see how long it would take for them to create a raft. Starting in a sphere shape, the ants were dropped into the water and made a 2 layer raft within 2 minutes. The ants have mastered this skill. 

This video shows how ants can float in water, and create an air layer where they can breathe.


    Dr. Hu decided to study how mosquitoes can fly in a rainstorm because one day it was pouring rain, and still his two year old son got a mosquito bite on his forehead. Dr. Hu didn’t think this would be possible because a water droplet weighs about 50 times the amount of a mosquito.  By doing experiments, Dr. Hu predicted that a mosquito flying in a rainstorm would be hit by a raindrop every 20 seconds. The mosquito can’t fly fast enough to outrun the water droplet, but is able to take the blows. After many experiments, and analyzing slow motion footage, Dr. Hu figured out that the mosquito is able to softly take the force of the rain droplet by accelerating downwards with the droplet. Therefore, there is not much of an impact, and the droplet doesn’t decelerate or impart a big force on the mosquito.

    The last thing that Dr. Hu presented on was how mammals are able to dry themselves off. When a human gets out of the shower, it is covered in a water layer about 1/50 of an inch thick and weighs approximately 1 pound. For mammals, this number is much larger because they have fur and it absorbs the water. The mammal doesn't have enough energy to evaporate the water through heat, and would therefore contract hypothermia. The shake method is a solution and is a far better use of their energy. He said most mammals are able to get rid of 70% of their water layer within 1 second. Mammals do this by twisting or wringing their bodies.  As a trend, the larger the mammal, the lower the frequency that the mammal has to shake to get rid of the water. When you watch the video, notice how larger animals shake slower than the smaller ones.

I really enjoyed Dr. Hu's presentation. I thank him for the research that he has done. It has inspired me to want to study these same topics.

For more information: http://www.biology.gatech.edu/people/david-hu