Boffins have created semi-autonomous microscopic robots that can organise themselves to assemble on the head of a pin.

Developed at Duke University, each micro-robot is shaped like a spatula but with dimensions measuring just microns, or millionths of a metre.

They are almost 100 times smaller than any previous robotic designs of their kind and weigh even less.

"It is marvellous to be able to do assembly and control at this fine a resolution with such very, very tiny things," said Bruce Donald, a professor of computer science and biochemistry at Duke University.

Formally known as microelectromechanical system micro-robots, the devices can be made to operate in the tiniest spaces.

In videos produced by the team, two micro-robots can be seen pirouetting to the music of a Strauss waltz on a dance floor just 1mm across.

"Our work constitutes the first implementation of an untethered, multi micro-robotic system," Donald's team said in its report.