When Insects Lost Their Homes, Evolution Clipped Their Wings

A study in New Zealand shows how man-made changes to an ecosystem can radically reshape the bodies of insect inhabitants.

New Zealand’s South Island was once covered in thick forest, the trees breaking like a dark green tide around the grassy mountaintops. After the arrival of Māori settlers about 750 years ago, some hillsides were cleared of their trees by humans using fire, and the foliage has not returned. For the organisms living in these forests, their habitat changed nearly overnight from sheltered woodland to exposed, windy grasslands. Since the forests burned, little winged insects called stoneflies have changed as well, researchers have found. In a kind of evolutionary pivot over the course of just a handful of centuries, the stoneflies living above the tree line have lost the ability to fly, suggesting that man-made changes to an ecosystem, such as deforestation, can radically reshape the bodies of its inhabitants. The discovery was published in the journal Biology Letters on Wednesday. Charles Darwin noticed that insects on islands have a curious tendency to be flightless, perhaps because flying is dangerous when you are tiny and winds are strong. In New Zealand, scientists had found flightless stoneflies on many different mountains, said Jon Waters, a professor at the University of Otago in New Zealand who is an author of the new paper. It was not initially clear why — whether there was something about the altitude that favored a flightless form, or if there was something else going on.