The first vehicle powered by evaporation frequently zooms along a laboratory bench these days at Columbia University. The 100-gram car relies on spore-coated tapes that expand and contract like tiny muscles as they move through environments of varying humidity. It can take up to 10 minutes to cross a table at the moment, but the biologists, chemists and engineers on the project think upgrades to the engine could enable it to power a wide range of technologies, including robotics systems and generators. For now the focus is on the small: another prototype can power two tiny LED lights.