Aquatic insects eat much of the debris from plants. Some aquatic insects are collectors which trap bits of debris to eat. Others are shredders. They cut up and eat leaves and other larger pieces of debris. Their leftovers become good pieces for bacteria or collectors to eat.
Some insects are scrapers.
They scrape algae and other material from the surfaces of rocks and logs in the stream. Shredders are most abundant in streams heavily shaded by deciduous trees. Collectors are often found in extremely high densities below the outlets of lakes because they collect lake plankton. Scrapers are most abundant in sunlit sections of the streams. They are often dominant in streams too wide to be covered with the canopy of trees.