A macro invertebrate behavior pattern keyed to the day/night
cycle (i.e., diurnal rhythm). Many species of arthropods participate
in drift each night during the summer months. Typically, organisms rise
up into the water column at two distinct times during the night; the
first at about 1 hour after dark and the second at 4-6 am. They drift
downstream until they reach the bottom of the pool in which they reside.
As morning approaches, they migrate long the bottom of the river back
to their original place of lift off. The purpose of drift is still being