The bright blue seed of the South American “bastard hogberry” has little nutritional value, but its bright color mimics that of a more nutritious seed, deceiving birds into eating the “ringer.” and spreading its seeds far and wide. Researchers at Harvard University, Cambridge, Mass., and the University of Exeter, U.K., used the bastard hogberry’s strategy to develop a new fiber that changes color when stretched. The photonic fibers are made by wrapping layers of polymer around a glass core that’s later etched away. The thickness of the layers determines the color of the fiber, a trick researchers learned from the exterior of the seed. Fibers that change color under strain could be used for smart sports textiles that change colors when muscles tense or signal an object’s expansion or contraction as the result of temperature change.