What's that bug?

[Wild One]

Recently I stopped in to observe a small, local pond. It was a sunny day, temps around 40-45ish and the pond has been ice-free for a couple weeks now. I observed several light-olive/cream-colored nymphs swimming toward the surface of the water, or just swimming along with the wind-blown current. This was awesome for me as I had never, in all my years of fishing, actually seen any aquatic insects swimming. I had a new found appreciation for some of our more popular nymph patterns and some enlightenment on how I could improve my patterns.

I went back two days later on a colder, cloudier day hoping to locate some of the rainbows that were stocked in this typical warm-water pond. I wasn't able to observe any of these nymphs; however, I saw a great number of shucks floating in the surface film and a good number of diptera (two-wing flies) flying a floating along as well. They were similar in color to the nymphs I observed a few days before, maybe a little darker olive. I readily recognized these flies as I have seen millions of them around just about every warm water lake or pond I've ever been to. They do not bite and would be equal in size to about a size 14 dry fly hook.

I am wondering if anyone out there knows a little about these flies. I've never seen them in or around any cold body of water (eventhough the water temp of this pond had to be less than 50). What are these flies? Do fish feed on them? What patterns are regularly used to imitate them? My first thought when I saw the nymphs was mayflies. This would hold true back home (March is famous for the first BWO hatches) but I don't know much about the midwest yet. Also, when I saw the adults flying around I knew they weren't mayflies. The adults hold their wings down against their backs almost like a caddis at rest, but they're flat and not tent-shaped.

I recently read a great article about chironomids and wonder if these are chironomids. I'm not familiar at all with chironomids. Is anyone out there familiar with these little flies/nymphs?