Sizes of bugs
This is a question that has perplexed me for a number of years and I'll try to answer you from a non professional standpoint as best as I can. It takes some history and follow up of most of the tailwaters to understand some of the things that has caused the situation that we find now on many tailwaters. For many years TVA did not see the beneficial aspects of tailwaters, nor how to manage them properly. Much of the management that you see today, where there are good populations of insects has come from the help and prodding of TU and TWRA. Basically, most tailwaters were dead from lack of oxygen and man caused pollution for lots of years after they were built by TVA. As understanding and enactment of laws took effect, we began to see changes. The addition of oxygen being added to tailwaters through weir dams and oxygen generators really was beneficial for miles downstream. These processes began to show effects through insect life and nice fish living for years. In some places, heavy generation has taken the types of bottoms that once held excellent insect life and made it impossible for that species to thrive. With the addition of silt on the bottom, you can see certain insects do quite well for a few years and then heavy generation changes those conditions. Water temps can also be a factor for some insects as well. The Hiawassee River has traditionally had an excellent population of insects because stream conditions and temperature are close to normal much of the time for good insect life. These conditions will change through the years and you will see ebbs and flows of different insects on various streams. It seems that the midge population has been able to survive thru most of the harsher conditions of the tailwaters and therefore are your predominant bugs each year. The bigger insects continue to have favourable conditions in the mountain streams. The fish adapt to either situation and flourish. Thank goodness for that. You'll get lots of other more professional thoughts about this matter and I would just try to store it for future use on the stream.