Fly Pattern - Furled Green Rockworm

Anyone who has turned over rocks in freestone streams has seen the abundant, small green, dark-headed worms that make such places home. Here is a good image of a specimen:

Arlen Thompson photograph:

The technical name for genus of this bug is Rhyacophila. Note several characteristics of this larva: its pronounced segmentation; its green color, and the fact that it has no case (“free-living”). They inhabit riffled water, similar to the water preferred by stoneflies. They are often found in the drift through either accidental event (washed away from a rock) or behavioral drift, where a large number of larvae will detach themselves from the rocks and drift to another part of the river. This behavior occurs at times in mid-morning and afternoon. Hatches occur in late morning or early afternoon, in my experience, from May through August.

Trout will graze on the drifting insects during these times. The hatching pupae are eaten in large numbers by trout during the hatch. Adults live for a couple of weeks, returning to the water where the females swim to the bottom of the stream and deposit their eggs. The adults are vulnerable to trout when they land on the water; when they swim to the bottom to deposit eggs; and when they again swim to the surface. Like all caddis, Rhyacophila go through a pupation period before hatching. They seal themselves inside a small chrysalis made of rocks and sand (called “periwinkles) by some.

This month’s fly represents one way to create a nice imitation of this insect’s larva stage. There are other ways—just do a Google search on “green rockworm” and you’ll find a wealth of information on the bug and on suitable imitations. I like the furled version since it is simple to tie, and it moves in the water in an enticing manner. See the GBF Fly Pattern Archive for another pattern from the GBF Fly Archive