Four years ago, Alexis Noel, a new doctoral student at the Georgia Institute of Technology, approached a dissection class with a strange request. When they were done cutting up their frogs, she asked, could she have the tongues? They said yes.
Noel has always loved frogs, so when she later joined David Hu’s biomechanics lab, she leapt at the chance to study them. Hu was keen, too. On a recent trip to the Atlanta Botanical Garden, he had watched a group of brightly colored poison arrow frogs being fed. In their movements, he saw a marvel of physics. They would launch their sticky tongues at insects with incredible speed and precision. When he later filmed a leopard frog with a high-speed camera, he showed that it can catch insects in less than 0.07 seconds—five times faster than a human blink. And when its tongue hits, the impact knocks the target away at an acceleration 12 times that of gravity. And yet, somehow, it doesn’t fly off. It sticks.
Try to design a wet material that can hit a highly textured object at incredibly high speed and adhere. You can’t. No one has. And yet frogs perform this feat every single time they eat. People have been studying frog tongues since the 19th century, but they’ve never understood exactly what makes them so sticky.
To find out, Noel gathered tongues from the dissection class, and—in the grand tradition of naturalists—prodded them with her finger. She and Hu were astonished at how soft the tongues were. “It’s like a piece of silly putty; when you touch it, you can’t tell if it’s a solid or a fluid,” Hu says. “And they were incredibly sticky. Freshly chewed chewing gum is similar, or marshmallow fluff that you can’t get off your hands.”