Bumblebees Can Switch to 'Economy Mode' When Their Nectar Load Gets Extra Heavy

Bumblebees can adjust the way they fly depending on how much weight they are carrying. (Photo: Dmitry Grigoriev [CC BY 2.0]/Flickr)

Bees are incredible. In addition to creating delicious honey, they're responsible for pollinating many flowers, fruits and vegetables and they work together in remarkable ways.

They're also capable of carrying nearly their body weight in nectar while flying, and scientists have recently learned out how they're able to perform this last feat.

Susan Gagliardi, a research associate in the College of Biological Sciences, and Stacey Combes, associate professor in the Department of Neurobiology, Physiology and Behavior, both at the University of California, Davis recently published a paper in Science Advances about their work.

The researchers attached various weights of solder wire to bumblebees that were contained within an enclosed space. They then measured how much energy the bees used. "We have the bees in a little chamber and we measure the carbon dioxide they produce. They are mostly burning sugar so you can tell directly how much sugar they are using as they are flying," Gagliardi said in a UC Davis news release.

Gagliardi and Combes found that the bees used less energy per unit of nectar when they were carrying more stuff. They then examined high-speed video of the experiment (above) to understand how that was possible. When carrying more weight, the bees beat their wings faster and higher — but at maximum weights, even using that extra energy isn't enough to keep them in the air.

They're able to stay airborne because they have an "economy mode," a previously unknown skill. The bees can move their wings differently when they're carrying the heaviest loads, which both enables them to stay in the air while still using less energy than their traditional flying mode. The bees can choose to turn it on and off, and it's not totally clear how it works, though the researchers do have a theory about changing wing rotation.

Why wouldn't the bees always use this more efficient mode regardless of the weight they're carrying? It's likely that there are other disadvantages to it — maybe over long periods it causes more fatigue, or maybe it's not as good for navigation. But the knowledge that bees can choose from various modes of flying to save energy was a surprise even to the scientists:

"When I started in this field there was a tendency to see them as little machines, we thought they’ll flap their wings one way when carrying zero load, another way when they’re carrying 50 percent load and every bee will do it the same way every time," Combes said. "This has given us an appreciation that it's a behavior, they choose what to do. Even the same bee on a different day will pick a new way to flap its wings."