Dry flies (except cdc based flies) are typically greased using floatants such Gink to help them float. CDC (Cul De Canard) fly patterns have ultra fine barbules in the cdc that help trap air to make the flies float. Check our blog post on treating dry flies here.
The flies we are trying to imitate hatch at different times of year, Mayflies are synonymous with Duffers Fortnight (in June!) Large Dark Olives hatch all year but Caenis only hatches in July to September. We produce monthly hatch charts for registered users showing you what hatches are anticipated and what flies will "match the hatch".
Dry Fly Patterns