I've got two fly fishing authors that paint the trike hatch in words for me...Hemingway and Marinaro:
"As far down the river as he could see, the trout were rising, making circles all down the surface of the water, as though it were starting to rain."-E.H. Big Two Hearted River
"As far as the eye could see,several hundred yards at least, the entire surface of the water was a mass of dimpling rise forms, occurring and recurring with increasing tempo as the evening advanced." V. Marinaro...A Modern Dry Fly Code.
The Trike hatch is my favorite fly fishing experience. I catch fish after fish after fish during the spinner fall....all my black and whites have always had tails as long as I could find and I never had a problem attracting or hooking a trout.
Size is all important, and be mindful that the bugs get smaller as the hatch progressive. When the fish are on #28 you're not going to do very well on #20. Here's a bowl full of #24...note the tails.
"As far down the river as he could see, the trout were rising, making circles on the surface of the water, as though it were starting to rain."- E.H., The Big Two Hearted River