name that hatch

I was fishing a stream in SE Minnesota (Driftless region) late into the
evening a couple of weeks ago. As the night fell there was the
beginnings of activity on the stream. I was able to get an occasional
take on very small flies (#22, #24 PTs) but it was clear that I was only
sort of close - didn't have the right fly.

The bats were also out in force but whatever they were taking, I
couldn't see it in the failing light. I pulled out my flashlight and
held it close to the water and saw a lot of very small insects in the
air a foot or two above the surface of the water.

With the light gone I gave up. On the way back to the car, I looked in
the webs along the stream side got a view of the bugs - they were light
colored, so small as to be transparent. In the dark and glare of the
flashlight, it was hard to tell much of anything about the flies - just
they were light colored and terribly small.

Three weeks later I was fishing the same stream in the daylight and came
across a large branch hung up in a riffle just downstream of where I had
been fishing before. The branch had been there for a while and was well
populated with spiders and their webs. On the webs I found a large
number of the flies described above. They were about 1/2 the size of a
trico and seemed to come in two varieties (male and female?) one was a
light cream color and the other was the same light cream with a light
tint of green - both were translucent. The two wings were largish and
clear - rather similar to the proportion as seen in the trico. I
couldn't see tails on these bugs - but I also don't really know how long
they'd been in the webs.

A friend with whom I fish another stream on the Wisconsin side of the
Driftless region has reported similar findings, and similar problems in
taking fish when they're hatching.

Anyone know what these flies are?

Larry