The Stream Doctor

December 29th, 2003

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

Q. From WTDURYEA: While fishing the Upper Sacramento (Calif), I stepped on what appeared to be a black rock and ended up with 52 degree water running over the top of my bib waders. On closer inspection, I observed that the rock was covered with tiny black worm-like creatures that seemed to curl up when disturbed. They were attached by one end and resided on a rock that was constantly wet but not entirely submerged. Do you know what they are? I have not seen any patterns that resemble these creatures, but I can't help but think they are a food source. I tied some imitations and am anxious to give them a try.

A. First of all, I'd be very hesitant (foolish?) trying to identify an organism without actually seeing it, but in your case, I'm pretty sure what you found. It sounds like a classic description of a rock covered with black fly larvae (Family Simuliidae). The larvae can literally cover rocks having a thin film of water going over them from which the larvae filter out fine organic particles with basket-like fans on their mouthparts. They are about a quarter of an inch long, attached by anal hooks to a silken pad they attach to the rock or vegetation surface, and can let themselves into the water column and then "reel" themselves back by a silk strand. They appear as tiny "bowling pins," with swollen abdomens; older ecologists, like me, who remember Lil Abner, liken them to schmoos. Trout do feed on them.

If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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