Starting in July, northern katydids use their wings to sing in the darkness. To lure a mate, a male (shown in photograph) scrapes together special structures on its forewings to create a distinctive, rasping call. But in the day, they stay quiet, and these bright-green insects—closely related to crickets, as well as grasshoppers and locusts—fade into the trees, often oaks, avoiding the attention of birds and other hunters.

At home in the eastern tier of the U.S. and in southeastern Canada, northern katydids were once considered uncommon. But entomologists found the katydids could be lured from the treetops with lights, and have identified more abundant populations. Still, the leaf-eating herbivores are vulnerable to decline, from such causes as light pollution, habitat fragmentation and pesticide use in both residential backyards and fields near forested lands.