If they are stuck onto something in running water they might be black fly
larva.
Whatever they are they are most likely the larva of some kind of insect. Over
5,000 species
of insects live part or all their lives in water in North America. Or they are
a worm of some sort. Toss a few to the fish and see if they don't scarf them up
right away... which is why you find these things in the filter, they don't last
very long in the pond being tasty and all.


kathy :-)
algae primer
http://hometown.aol.com/ka30p/myhomepage/garden.html