You can use this pattern in nearly every season. The Blue Wing Olive mirrors the callibaetis dun hatch, which usually occurs during wet and nasty weather. The duller color won't spook fish feeding on the top on thhese gray days. Per 12. Sizes: 16, 18, 20. Cancer and Reproductive Harm- www.P65Warnings.ca.gov. Type: Fly Assortments.