Earlier this summer, I decided to try a size 18 grey scud that I had in my box. The gills wouldn't stop eating it! I finally got around to tying up some more. These are a little bigger, a size 16.
BBFisher, the one time I fished the 18's, I don't think they swallowed them, but that was sheer luck. I've fished similar sized bugs before, and yes, some of them were swallowed.