The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
the more important feature to me is the the core of most chenille is cotton thread and the core of vernille is some sort of plastic thread
That becomes important when tying San Juan Worms or Poopah Caddis patterns. Both patterns call for melting the material so the exposed ends don't unravel. The chenille cotton core burns rather than melting..