Buck, I have seen what I think you are talking about down on the Kentucky River. I have no idea what their scientific name is but I refer to them as glow bugs.:D The ones I have seen look like a little centipede or some people call them sow bugs, or ball bugs. They are grey in the daytime and glow under light in the nightime. They are very small, maybe a 1/4 inch up to 1/2 inch in length. I use to catfish the river during the summer months and we would see them down there at night. I wish I could tell you more, but I am pretty sure thats sound's like what you are describing. I don't know what they are doing all gathered up like that on the bank, but that's the way we use to see them down there. A bunch of them all gathered on one or two banks.

Weird stuff.

Chris