Giant Chinese Dobsonfly (Acanthacorydalis fruhstorferi)

In truth, it may not be such a problem if they really were useless. Adult dobsonflies only live for about a week, it looks like they don't even need to eat. Instead, they spend most of their lives, several years, as freshwater larvae called hellgrammites. These have all the gills they need and strong (and short) pincers for eating the larvae of other insects. They are not great swimmers, spending most of their time under rocks. They also have small hooks at the tip of their tail for gripping, so that they don't get swept away in rivers and streams.