"To date, swimming soft robots have not been able to swim faster than one body length per second, but marine animals -- such as manta rays -- are able to swim much faster, and much more efficiently," says Jie Yin, corresponding author of a paper on the work and an associate professor of mechanical and aerospace engineering at NC State. "We wanted to draw on the biomechanics of these animals to see if we could develop faster, more energy-efficient soft robots. The prototypes we've developed work exceptionally well." The researchers developed two types of butterfly bots. One was built specifically for speed, and was able to reach average speeds of 3.74 body lengths per second.