An insect (order Plecoptera), most of which have membranous wings that fold flat against the back when the insect is at rest, and a pair of long, needle-like cerci projecting from the tip of the abdomen. They live near water and the nymphs, called naiads, resemble wingless adults with external gills, and inhabit the bottom of well-oxygenated fresh lakes and rivers. There are about 3500 species found worldwide.