I have never seen these flies mentioned in a fly fishing book, entomology-oriented or otherwise. However, a large number of their larvae turned up in my early-July kicknet samples on the Gallatin River near Big Sky, Montana, which led me to photograph one and search Google for mentions. A couple other angler-scientists have written about them online:
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Larvae: Many classes of aquatic insects, such as caddisflies, midges, craneflies, dobsonflies, alderflies, and many more, are known as "larvae" rather than "nymphs" in their juvenile stages. They have mostly soft bodies rather than hard exoskeletons. These insects also advance through a "pupa" stage before reaching adulthood.