Though grasses don't provide nectar they have masses of pollen as anyone with hay fever will tell you. Though butterflies won't eat pollen many species depend on grasses as a food plant for their larvae and bees most certainly do harvest pollen and I have observed bees doing so on the grasses I mentioned above. It was more than obvious that is exactly what they were doing, as I said they were quite methodical about their behaviour. Pollen provides protein, carbohydrates lipids, sugar etc. There is absolutely no reason to assume that the ready supply of pollen in a grass flower head is of any less of nutritional value to a bee than from a dicotyledonous flower.
Hole reported in 1911 bees collecting pollen from grasses in India. Burtt Davey in 1914 mentions bees collecting pollen from maze in Kenya. In 1933 Richards and Davies describe pollination by Melipona bees of Pariana grass.
Grasses and the Butterflies that feed on them:
Blue Moon Grass (Sesleria caerulea) food plant for Scotch Argus
Creeping Soft Grass (Holcus mollis) - Essex Skipper & Small Skipper
Downy Oat Grass (Helictotrichon pubescens) - Meadow Brown
Early Hair Grass (Aira praecox) - Grayling
Various grasses - Arran Brown
One of the best is Yorkshire Fog Holcus which supports
Speckled Wood &
Yorkshire fog is a very nice wild grass, it has pinky mauve flowers and very tactile too. Please see:
Sweet vernal-grass - Anthoxanthum odoratum may be one of the food plants for the larvae of butterflies in the brown and skipper families