To test the robot prototype, Bergbreiter hooked it up so that rather than the bot actually jumping, its leg was positioned to kick an object. This allowed her to calculate the energy being released. So far Bergbreiter has only tried partially stretching the rubber band, which would achieve a jump of about 12 millimeters for the 10-milligram robot. However, she says that based on the results of this test, a full stretch would be capable of producing jumps as high as 200 millimeters, and they would cover roughly twice as much ground horizontally. The results will be presented next week at the International Conference on Robotics and Automation, in Rome, Italy.

The current seven-millimeter-long prototype is still much larger than a flea. But Bergbreiter is keen to shrink the robot down to about one millimeter, or flea size. Also, she still needs to add the tiny photovoltaic solar cell that has been fabricated separately. "The next step is to put it all together," she says.

One of the benefits of making robots on the insect scale is that it is possible to generate very high takeoff velocities. This is why insects can achieve such relatively huge jumps. As an object's volume is reduced, its mass diminishes at a much greater rate, which in turn allows for great accelerations.

However, there is a trade-off. "Drag increases as you get smaller," says Bergbreiter. So the trick is to ensure that the bots' size offers enough benefits in terms of acceleration to outweigh the cost of any additional drag.

But generating this movement still requires more energy than the robot is capable of scavenging from its environment through its solar cells. This is often the case with autonomous robots, which is why storing the energy is necessary, says Chris Melhuish, a professor of robotics and director of the Bristol Robotics Laboratory at the University of Bristol and the University of the West of England, U.K.

It's probable that the only other way to cover such relatively large distances is through flight. "But flying adds a whole new set of challenges," says Bergbreiter. It requires very high-powered motors to flap wings or drive a propeller, and given the effect that wind can have on such small objects, there are major control issues. Jumping, on the other hand, would allow robots to move much greater distances without huge power requirements.