By observing manta rays in the wild, modeling them, and building robots, researchers are learning how these agile animals ply the ocean. Swimming like butterﬂies underwater, with mesmerizing ease and grace, manta rays are the envy of engineers seeking more efficient underwater vehicles. For the past 3 years, researchers at Princeton University and the University of Virginia have been working to understand how these meters-wide ﬁsh are so light on their ﬁns. Now, their students are putting the insights they have gained to the test in a manta robot competition between the two collaborating universities. Read more from sciencemag.org: Manta Machines.