Flowers 'advertise' the presence of nectar to bees using electrical signals, say University of Bristol researchers, by indicating whether they've recently been visited by another bee.
Plants are usually charged negatively and emit weak electric fields; while bees acquire a positive charge as they fly through the air. While sparks don't actually fly as a charged bee approaches a charged flower, a small electric force builds up that can potentially convey information.
"This novel communication channel reveals how flowers can potentially inform their pollinators about the honest status of their precious nectar and pollen reserves," says Dr Heather Whitney, a co-author of the study.
By placing electrodes in the stems of petunias, the researchers showed that when a bee lands, the flower's electrical potential changes and remains so for several minutes. And, they found, bumblebees can detect and distinguish between different floral electric fields, letting them know whether another bee has recently visited.
The team isn't sure just how the bees detect electric fields - although they speculate that it's the same electrostatic force that makes your hair stand up after brushing, affecting the bumblebees' hairy bodies.
The discovery of such electric detection has opened up a whole new understanding of insect perception and flower communication, says lead author Professor Daniel Robert.
"The last thing a flower wants is to attract a bee and then fail to provide nectar: a lesson in honest advertising since bees are good learners and would soon lose interest in such an unrewarding flower," he says.
"The co-evolution between flowers and bees has a long and beneficial history, so perhaps it's not entirely surprising that we are still discovering today how remarkably sophisticated their communication is."