my procedure was a failure.
i was at ISO 100. i left the shutter open, camera on a tripod pointed at the grass. i tried like 5 sec, 8 sec, 15 sec exposures.
i eventually got enough light in to make it look like daytime in my picture, but couldn't see the fireflies...very faintly in one shot.
they were everywhere last night....tonight i will try increasing the ISO to 400, 800, 1600...and see if i can capture enough of them on a shorter exposure...1-2-4- sseconds.