Mayfly offspring begin life as a nymph, which resides beneath the surface, clinging to rocks and debris located along the bottom, or burrowed in the sand. Usually capable of limited swimming ability, mayfly nymphs live underwater for six to twelve months, and sometimes longer. During that time, they may shed their nymphal outer shell more than one time to accommodate growth. Upon reaching maturity, mayflies emerge to the surface as winged duns. Once airborne, the duns undergo a second metamorphosis, to become breeding adults.
Adults return to the streams in great swarms to perform their famous mating dance.
Unable to feed because they have no mouth, adult mayflies mate, and they fall spent on the surface of the water, where waiting trout seize these protein-rich morsels thus completing their life cycle. Caddis flies also begin life as waterborne sub-adult. Rather than being nymphs, though, caddis fly offspring are what biologists refer to as pupa. Whereas a mayfly nymph is a well-armored creature complete with legs and most other visible attributes of an insect, a caddis fly pupa usually looks like a plump, soft little worm resembling a common grub. In His infinite wisdom though, the Creator endowed the caddis fly pupa with all of the tools needed not only to survive in the hostile surroundings of a trout stream, but also to prosper.