One of the very first insects you will want to imitate when the season first opens in Yellowstone National Park are the Blue-winged olives. They can be one of the most complicated common names of all aquatic insects simply because it has so many different species that vary slightly in color and a lot in size. Most of the fishing that first occurs in the park during the opening week will be done on the Firehole River simply because the water will be warmer there than any other stream except some very small ones. Most of them will be Baetis species but other know as little Blue-winged olives may include Acentrella, Diphetor and Plauditus species. We will be covering other important hatches as we move along getting closer to the open fishing season. Here is a copy of our Firehole River Hatch Chart.