RIO Products BWO Dry Flies Assortment - BWO is short for Blue Winged Olive but is also referred to as a baetis. These are tiny Mayflies that can hatch any time of year, but primarily in the cooler months of Fall, Winter and Spring. Their colors are pale olive to dark olive. Blue Winged Olives are a very important food for trout and this assortment consists of our bestselling sizes and patterns that represent BWO dries. INCLUDES 7 FLIES: This dry fly kit includes 12 flies designed to improve you're time on the water. FRESHWATER FLY KIT: Desgined to catch Trout in lakes, streams, rivers, and ponds.