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.
Chironomid pupae range from under 1/8" to over 1 inch in length; the nickname "bomber" refers to the larger pupae. Phillip Rowley, BC & AB author of Fly Patterns for Stillwaters: A study of Trout, Entomology and Tying, page 11.