Them little suckers eat 'em all up fast!! Made me laugh when I put one
in the settling tank, he ate all the larvae, then got sucked into the
pump and ended up in the filters. Still swimmin' around. Maybe he'll
make it down stream and into the pond!
http://www.bunchobikes.com/pond6.htm .

Dances With Ferrets wrote:

They may be black fly larvae.... which thrive in not-too-warm rapidly
moving water... where they attach to rocks or any non-mobile
substrate. Mosquito larvae can still live in moving water.... so long
as there is even the smallest dead or near-dead spot in the water
course where they can exist. Never heard of them living in the actual
stream of flowing water.