You wouldn’t know this teensy speck was a robot if you saw it. At less than a millimeter across, you might not notice it at all. But the itty-bitty machine offers big opportunities to explore the microscopic world. It’s the smallest robot that can move, think and act on its own, its creators say.

The mini robot was inspired by nature’s tiny, complex machines. “Cells and microorganisms are phenomenally sophisticated,” says Marc Miskin. “Nature has chosen this length scale to organize all of life.” An engineer, Miskin works at the University of Pennsylvania in Philadelphia. He hopes that similarly tiny robots will help uncover the secrets of the cellular realm.

The new robot is as small as a paramecium — a single-celled organism that lives in water. It isn’t the first machine less than a millimeter long, Miskin says. But it’s the first one that’s fully autonomous. Once programmed, it decides where to go, how to get there and what to do.

Such small robots might someday be able to travel through the human body to study cells or deliver drugs.