The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
In 4 records from GBIF, adults of this genus have been collected during June (50%) and April (50%).
To determine whether a specimen of Rhyacophilidae belongs to Himalopsyche, use the Key to Genera of Rhyacophilidae Adults.