This walking microrobot is smaller than an ant's head
The 3D-printed robot above weighs just one milligram and is only 2.5mm at its longest point. Designed by University of Maryland mechanical engineer Ryan St. Pierre and his colleagues, it is likely the smallest walking robot in the world. Video of the microbot scurrying along is below. From IEEE Spectrum:
Like its predecessors, this robot is far too small for traditional motors or electronics. Its legs are controlled by external magnetic fields acting on tiny cubic magnets embedded in the robot’s hips. Rotating magnetic fields cause the magnets to rotate, driving the legs at speeds of up to 150 Hz. With all of the magnets installed into the hips in the same orientation, you get a pronking gait, but other gaits are possible by shifting the magnets around a bit. Top speed is an impressive 37.3 mm/s, or 14.9 body lengths per second, and somewhat surprisingly, the robot seems to be quite durable—it was tested for 1,000,000 actuation cycles “with no signs of visible wear or decreased performance.”