Before youre standing in the water with a thick cloud of baetis mayflies coming down, stock your box with the Blue-Winged Olives 12-Pack Flies to avoid feeling like youve been kicked in the gut! Blue Winged Olives are so productive that some fly fishermen dedicate a whole fly box to house this pattern. Per 12. Hook sizes: #20, #18, #16. Color: (009)Olive. Cancer and Reproductive Harm- www.P65Warnings.ca.gov. Type: Flies.