Flowers generate electrostatic fields as a kind of 'gas gauge' for available nectar, see:
Detection and Learning of Floral Electric Fields by Bumblebees by Dominic Clarke et al. Science 340, 66 (2013); DOI: 10.1126/science.1230883 http://science.sciencemag.org/content/340/6128/66
https://www.npr.org/2013/02/22/172611866/honey-its-electric-...