Krystal Flash Pupa - Larva & Pupa. Fished directly before a Caddis hatch the Krystal Flash Pupa is guaranteed to bring in a trout, right before the hatch the ravenous trout is eagerly waiting for a rogue caddis to begin its ascent to the surface early, it is then the trout will gobble up the easy prey; therefore to mimic such an event can provide devastating results.