It's relatively easy to study animals' movement by plunking them on treadmills, but how do you do that with a creature as small and fragile as ants? Build a tiny custom treadmill, that's how. Scientists have crafted a contraption that let them study the homing behavior of ants on a treadmill for the first time. In many ways, it amounts to an optical mouse flipped on its back. An air-cushioned styrofoam ball serves as the actual running surface, giving the ant freedom to move as far as the tether (dental floss) allows without falling off; optical sensors from computer mice track their gait, speed and changes in direction.