My honey bee water foraging station, this year, includes some sections of stalks from last season's Sunflowers. I put them in the water so that the bees can land safely and draw up water into their nectar crops.
But, the bees have also been mining some kind of mineral or nutrient out of the insides and ends of the stalks.
If you have empirical knowledge of what they're harvesting, please leave a comment. Thanks!