Skwala or Spring Stone

Skwala americana (formerly Skwala parallela)

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 The Skwala Stone emergence is the first important hatch of the season.  Adults begin to appear during the last week or two of February and fish begin to key on them by the first or second week of  March.  The hatch lasts well into April and overlaps March Brown and BWO hatches.  Skwala generally emerge at night, crawling onto rocks close to the shore.  Mating often occurs as soon as the female frees herself from the nymphal shuck.  Skwala adults become important as trout food when the females return to the river to lay eggs, usually in the late afternoon and evening.  Nymphs prefer fast, rocky runs and riffles and migrate to slower water to emerge.  Emergence takes place on shore.  

Golden Stone (pacifica)

Hesperoperla pacifica  (formerly Acroneuria pacifica) 
Calineuria californica  (formerly Acroneuria californica)

Much less important on the Yakima than Skwala americana and Claassenia sabulosa.  Can be important locally and their numbers seem to be growing, particularly pacifica. The size of the emergence varies greatly from year to year.  Pacifica is  more common than californica.  Emergence usually occurs in the late afternoon and evening.  Egg laying activity is generally in the evening.  Nymphs prefer fast, rocky runs and riffles and migrate to slower water to emerge.   Emergence takes place on shore.    

Yellow Sally

Isoperla / Osobenus

Yellow Sally is a generic term applied to any small yellow stonefly.  They are active on the Yakima from May through August.  Emergence  occurs during daylight hours and egg laying in late afternoon and evening.   Nymphs prefer moderate to fast runs and riffles and migrate to slower water to emerge.  Emergence takes place on shore.           

Summer Stone (Shortwing Stone)

Claassenia sabulosa

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