We’ve got a new world record: Size for size, the Southern California erythracaridis mite species, Paratarsotomus macropalpis, is the fastest runner on Earth. If we moved as quickly as these guys do, extrapolated to our size, we’d run over 2,000 kilometers an hour.
Running on concrete, these sesame seed-sized mites traveled at an average speed of 192.4 body lengths per second, a measure of speed relative to size. Their peak speed was 322 body lengths per second.
Those easily exceed the highest documented speed for land animals: the Australian tiger beetle, which tops out at 171 body lengths per second. Cheetahs, who’ve clocked in around 96 kilometers per hour, are still the world’s fastest land animals absolutely, though they move just 16 body lengths per second.
The mite-y fast predators, first identified in 1916, are often seen running along rocks and sidewalks in desert climates. A team led by Samuel Rubin from Pitzer College filmed the small mites using a high frame-rate video camera in the field to analyze their speed, stride frequency, acceleration, and deceleration. Recording them was no easy feat, since the camera’s field of view is only about 10 centimeters wide. The mites were running on concrete at high temperatures (40 to 60 degrees Celsius), much higher than the upper lethal limit for most animals.
Back in the lab, the team filmed the mites starting, stopping, and turning in order to analyze their gait and kinematic mechanisms. Watch the video. In addition to their exceptional speeds, the mites also showed exceptionally high stride frequencies -- as fast as 135 Hz, meaning they picked up and put down each foot about 135 times a second. This increased significantly with substrate temperature.
Relative speed and stride frequency increase as animals get smaller, and in theory, muscle physiology should at some point limit how fast a leg can move. "When the values for mites are compared with data from other animals, they indicate that, if there is an upper limit, we haven't found it yet,” study coauthor Jonathan Wright of Pomona College says.
The mites also accelerate and decelerate rapidly, with average values of 7.2 and −10.1 meters per second squared, respectively. The forces are likely thanks to a combination of muscle and cuticle ligament strain.
“It’s so cool to discover something that’s faster than anything else, and just to imagine, as a human, going that fast compared to your body length is really amazing,” Rubin says in a press release. "But beyond that, looking deeper into the physics of how they accomplish these speeds could help inspire revolutionary new designs for things like robots or biomimetic devices." Being able to stop and change directions quickly with ease are useful traits for nimble, superfast bots.
The findings were reported at the Experimental Biology 2014 meeting in San Diego this week. They were also published in the Federation of American Societies for Experimental Biology (FASEB) Journal.
Image: Samuel Rubin (W.M. Keck Science Center, Pitzer College), Dr. J.C. Wright Laboratory (Department of Biology, Pomona College), the Claremont University Consortium, Claremont, CA
