The Southern California erythracarid mite species, Paratarsotomus macropalpis, was filmed using a high frame-rate video camera in the field to analyze speed, stride frequency, acceleration and deceleration. We also recorded higher resolution lab footage of mites starting, stopping and turning to analyze gait and kinematic mechanisms. Mites running in the field on concrete substrates at high temperatures (40°C to 60°C) were shown to travel at mean relative speed of 192.4 bl s−1 (body lengths per second), exceeding the highest currently documented speed for land animals (171 bl s−1).
Despite this exceptional value, it conforms broadly with predictions based on interspecific scaling. Stride frequencies were also exceptionally high (as fast as 135 Hz), and increased significantly with substrate temperature. Mites accelerate and decelerate rapidly (mean values of 7.2 ms−2 and −10.1 ms−2, respectively), although the forces involved are simiilar to those found in other running animals. Calculations show that air resistance is a minor contributor to deceleration; the forces are likely borne by a combination of muscle and cuticle ligament strain. During normal running, adjacent and opposite tarsi are 180 degrees out of phase. This gait cycle is preserved during turning, although the two front pairs of tarsi initiate acceleration cycles and duty factors increase for inner tarsi during turns.
For comparison, a cheetah running about 96 kilometers per hour moves about 16 body lengths per second—and humans covering ground as fast as this mite does could run more than 2,000 km/hr. Future studies of these mites (which pick up and put down each foot about 135 times a second) could help engineers develop superfast, superagile robots.