Chironomid (from Nymphs by Ernest Schwiebert):

There are many, many species of these elegant little Chironomodae midges. They hatch sporadically from early spring to deep autumn, and on some rivers there are extensive winter cycles of emergence.

Although their most impressive populations are found in lakes and impoundments, the Chironomodae are also a primary component of the trout diet in large, slow-flowing streams. The adults are rather long-legged flies with bodies slightly longer than their wings. Size ranges from one-eighth inch to one-half inch in length. The wings are pale-grayish or white, and in some species are held tightly along their body, while others spread them wide.

During their transformation from the larval stage to the point of pupal emergence, the Chironomodae are available to fish in almost astronomical numbers.

Thanks to the efforts of swapmeister John Abbott, we now have a nice pile of these tiny flies to toss at those finicky fishes.