Coffinflies originally got their name because some species were found in exhumed coffins. Their larvae burrowed deep in the ground to the body inside the coffin and aided decomposition. This particular species prefers a water environment, not earth, in its larval stage, and adults can be found in the hundreds of thousands from the spring to summer if the water source is clean and unpolluted.
The larvae look like small versions of lobsters, or crayfish, and they live that younger phase of their lives completely under water. They burrow into the sediment or sand at the bottom of the pond or lake and feed on algae and plant matter. Because they are still developing while living in water, larvae can be indicators of a water system's cleanliness. Even moderate levels of pollution have been known to obliterate a population of larvae in a dirty body of water.
The Coffinfly undergoes a series of molts (phase changes) as it matures to its adult form. One intermediate phase, called the subimago, includes the formation of wings and tiny hairs that start to prevent them from submerging under water. Anglers (fishermen and women) call this phase a "dun" and may use larvae, or plastic replications of them, as bait to catch certain species of fish that naturally feed on them. After another molt, they become more mature adults called imago, which are known as "spinners" to anglers.
Adults are land-bound and do not feed. Their live span at this stage is very short, leaving only enough time to reproduce before dying. Adults are attracted to lights and may end up flying to them and dying near them by the hundreds.