Brachycentrus occidentalis / Brachycentrus americanus
American Grannom (Mother’s Day Caddis) larvae build rectangular, tapered cases, prefer moderate to fast riffles and runs and emerge midstream. Occidentalis is the first important Caddis emergence of the year, beginning in the last week or two of April and continuing through June. Peak emergence usually occurs from the last week of April until the last week of May. The first few weeks can produce incredible numbers of adults. Americanus begins to emerge in June and continues through August. The emergence is much smaller than occidentalis, but is a significant hatch on the Yakima.
occidentalis: Size 16 to 18 - Color: wings: tan. body: dark olive to black with an olive lateral line on the abdomen.
Spotted Sedge are case-less caddis that build small nets to seine food from the current, prefer moderate to fast riffles and runs and emerge midstream. Hydropsyche can begin emerging in spring, generally during the afternoon, but the heaviest emergences usually occur in July and August in the evening.
Larva: Size 14 to 18 - Color: light olive brown to dark olive brown. Adult: Size 14 to 18 - Color: wings: tan. body: tan to light brown.
Emerger: brown and golden tan or dark dun and dark golden brown.
Little Sister Sedge. These case-less caddis build small nets to seine food from the current, prefer moderate to fast riffles and runs and emerge midstream. Cheumatopsyche are active from April to August and are mostly daytime emergers on the Yakima.
Larva: Size 16 to 18. Color: Light olive brown to dark olive brown.
October Caddis. The largest caddis in the Yakima. The larva build a case from small pebbles and live in moderate to fast flows. Most mature larva migrate to the slower, shallower margins of the river in July and August and attach themselves to rocks or other structure to begin pupation. The mature pupa leaves it case and will either swim to the surface or crawl to the shoreline to emerge. Emergence typically takes place in September on the Yakima.
The Yakima drops dramatically in late August and September due to the “flip-flop”. Large numbers of the pupating Octobers are left high and dry during this period and die. The survival rate for those that pupate in deeper water is much greater. A good number of these will swim to the surface to emerge.