Bumblebees build up a positive electric charge as they fly, the same static effect as rubbing a balloon on your hair. Flowers carry a slight negative charge from the atmosphere.
When a bee lands on a flower, the two exchange charge. The flower's electric signature stays altered for about 100 seconds, effectively hanging a "just visited" sign that other bees can detect and skip.
In 2013, researchers at the University of Bristol showed that bees can learn to read these electric fields to tell rewarding flowers from duds, even with all visual and scent cues removed.
A 2016 follow-up found the mechanism: fine body hairs that physically bend in response to electric gradients as weak as a few volts per meter. This was the first dry electroreception system found in a land animal. Before this, electroreception was only known in aquatic species like sharks and rays.
Flowers broadcast their status on a channel humans had no idea existed. A bee approaching a recently visited flower senses the weakened field, veers away, and saves the trip.
Clarke et al., Science 340, 2013. Sutton et al., PNAS 113, 2016. University of Bristol.