How do bees, either bumblebees or honey bees, collect nectar and pollen as efficiently as possible? This activity is called foraging, and it is central to the success of any social bee colony.
Foraging has been studied best in honey bees, and they are known to use a variety of techniques including aromas, communicating flower location, and scent marking to ensure that individual workers do not waste a lot of time looking for food in unlikely places.
Bumblebees also use scent marking to improve their foraging efficiency. Apparently it works like this. Each bumblebee body is coated with a number of chemicals that serve to waterproof its exoskeleton. As a bee walks over the surface of a flower collecting nectar and pollen its feet leave traces of these chemicals behind.
The next bee to come along can detect the presence of the chemical marker left by the previous forager using sensory organs in its antennae. Bumblebees can often be seen hovering just in front a flower before deciding to alight or instead to move on to the next blossom. It seems that if the bee finds that another has just been working on the flower, it moves on, knowing that the nectar in that flower has probably been used up.
So bumblebees warn each other off a flower that has little nectar left. And honey bees do the same thing. The chemical markers used by different species are fairly similar, and it seems that bumblebees can recognize the 'no nectar' signal left by honey bees.
This chemical marking behavior is probably why you never seem to see bees fighting over a flower. It's a way to ensure that all of them make the best use of their time in the field.
But it also suggests that if you have a lot of foraging honey bees out there marking flowers with 'no nectar' signs, there may not be much left over for the less abundant bumblebees.
[Honey bee and bumblebee photos by D. Barr]