While trekking through the Peruvian rain forest, an eight-hour boat ride from the nearest jungle settlement, biologist Aaron Pomerantz saw what seemed like tiny invisible jets zipping across the trail. “I was out there with a net trying to catch things,” he says, “and these just changed direction and vanished.”
It was his first close encounter with clear-winged butterflies, insects that inhabit Central and South American forests and have a remarkable means of camouflage: see-through or “glass” wings that make them particularly hard to spot in the dense understory.
“It’s like the power of invisibility,” says Pomerantz, lead author of a recent study in the Journal of Experimental Biology that examines how clear wings develop. “If you can put on an invisibility cloak, it’s a lot harder for predators to find you. In ocean environments there are lots of transparent species, but on land it’s much less common. And that really gets into the question of, ‘What does it take to be transparent on land?’”
By studying the wings of the species Greta oto, also known as the glasswing butterfly, at various stages of pupal development, Pomerantz and his colleagues at the University of California, Berkeley, the Marine Biological Laboratory in Woods Hole, and Caltech, found a few factors. There are modifications in the shape and density of the microscopic scales that typically create a butterfly’s colorful patterns. A layer of teeny waxy pillars also acts like an extra antiglare coating.