When I first started tying flies many years ago, I figured an appropriately sized rusty spinner should work.
And not long afterward, I hit a nice BWO spinner fall on the little j.
These were the large ones - Drunella genus. And I could hardly catch a fish matching them them with those rusty spinners.
So, I caught a few specimens, and examined them closely. And I found out that their bodies were a distinct olive grayish/brown color.
So, I went back to the vise - and tied some with an olive cast.
It has now been a good 25 years or more since that happened. And I haven't hit a good BWO spinner fall since, to give them a try on.