NEW ORLEANS, LOUISIANA—Aerospace engineers are always on the lookout for ways to make flying more efficient. Now, they’ve discovered a trick from nature that can do just that: the scales on butterfly wings. Those incredibly tiny scales—about 0.1 millimeter long—are arranged like roof shingles on the wing, making it a little rough. But until now, no one knew how that roughness affected flight. So a group of engineers filmed 11 free-flying monarch butterflies, first with their scales and then after their scales had been stripped off. Using a special chamber with 22 cameras to track the insects with submillimeter precision, they found that the scales boosted climbing efficiency between 16% and 82%, they reported today at the annual meeting of the Society for Integrative and Comparative Biology (see video above). Scaleless butterflies flapped their wings just as quickly, but not as broadly, as those with scales, they reported. When the researchers made artificial wings, they discovered that the scales affect the air circling around the upper surface of the wing, likely enhancing lift. This suggests that even if scales aren’t necessary for flight (as some biologists thought), they do improve performance. The researchers think scales may also help flight in other, still unknown ways. For monarchs, which make annual long-distance migrations of up to 4000 kilometers, even a slight advantage could go a long way in helping them reach their destination. And scales may one day help the engineers, too, by improving the design of small flying robots.