I looked out the patio door a few hours after the light rain ended and saw a number of small insects fluttered around the back yard. At that time, the insects were all flying around so I was not able to see much detail or get pictures of the insects. I was able to see that the insects had two pairs of slender, transparent wings.
A couple of hours later after I photographed the fly with black and clear wings, I spotted a fluttering motion on a buckwheat flower cluster. I think that the four transparent wings on the right side of the flower cluster belong to an insect of the type I saw earlier in flight.
Since the insects appeared in large numbers suddenly, I suspected that they had emerged after the rain.