"In the beds of all our larger lakes and streams there exists a vast animal population, dependent, directly of indirectly, upon the rich organic food substances that are bestowed by gravity upon the bottom. Many fishes wander about over the bottom foraging. Many , heavily armored and slow, go pushing their way and leaving tralis through the bottom sand and sediment. And many smaller animals burrow, some by digging their way like moles, as do the and of gomphine dragonflies; some by "worming" their way through the soil, as do the larvae of and many . Among the burrowers none are more abundant or more important than the young of the mayflies. Indeed, there are hardly any aquatic organisms of greater , for they are among the principal herbivores of the waters, and they are all choice food for fishes. How abundant there are in all our large lakes and streams is well attested by the vast hordes of adults that appear in the air at the times of their annual swarming. They issue from the water mainly at night."