447
As Heath Ogden, a professor of evolutionary biology at Utah Valley University, observed, these insects first appeared about 350 million years ago, and evolution has shown that spending most of their lives as nymphs is a good strategy because they store energy in that form, and as adults, they gain a mechanism for flight, reproduction, and egg laying.
The shortest lifespan was observed in the species Dolania americana, where males live less than an hour as adults and females have only five minutes to mate and lay eggs before dying.