Scientists have created the world’s first living, self-healing robots using stem cells from frogs.

Named xenobots after the African clawed frog (Xenopus laevis) from which they take their stem cells, the machines are less than a millimeter (0.04 inches) wide — small enough to travel inside human bodies. They can walk and swim, survive for weeks without food and work together in groups.

These are “entirely new life-forms,” said the University of Vermont, which conducted the research with Tufts University.