Scientists have found that the thicker and sweeter the nectar is, the harder it is for bees to swallow and regurgitate it. When it comes to nectar, sugar slows down the bees because it takes too much of their energy, so sweeter is not necessarily better according to new research. Yet sugar is what makes the nectar so appealing, and the more sugar contained in the nectar, the more energy it contains.

Bumblebees drink nectar from flowers, then vomit it up in their nest so it can be used by other bees in the colony. A report in the Journal of the Royal Society Interface studied both nectar drinking and regurgitation in a bumblebee commonly found in the UK – Bombus terrestris – or buff-tailed bumblebee.

Nectar gets thicker and stickier as the sugar content increases and this makes it challenging for bees to drink and regurgitate, costing them more time and energy, scientists say. Nectar that is low in sugar is easier for bees to drink, and easier to vomit up. As it gets more sugar-rich, it takes bees longer to drink and rapidly becomes more exhausting to vomit.

This 1:24-minute long video shows how the research was done:



First author of the study is Dr. Jonathan Pattrick, former PhD student based jointly at the University of Cambridge’s departments of zoology and plant sciences. He is now a post-doctoral researcher at the University of Oxford’s Department of Zoology. He indicates that nectar sugar concentration affects the speed of a bee’s foraging trips, so whether or not to consume it influences her foraging decisions. The bumblebee must find a balance in choosing an energy-rich nectar that isn’t too time consuming to drink and regurgitate. Scientists have long known that higher-sugar-content nectar takes bees longer to drink, but the fact that it slows nectar regurgitation did not receive much attention.

During the research in the Department of Plant Science’s Bee Lab, bees were able to forage on sugar solutions in three different concentrations. They were timed and weighed. When they returned to their “nest,” researchers timed how long it took for them to vomit up the nectar they had collected.

Dr. Pattrick said that for low strength nectar, bees had a quick vomit that only lasted a few seconds and went back out foraging. But for really thick nectar it took them ages to vomit, and some strained with it for nearly a minute. He observed that it’s hard enough to drink a thick, sticky liquid, but trying to spit it out again through a straw is even harder.

At a certain sugar concentration, or “sweet spot” the energy gain compared to the energy loss is optimized for nectar feeders. For any nectar concentration, bees regurgitated the nectar quicker than they originally drank it. But as nectar sugar concentration rises, as well as stickiness, the rate of vomiting it out decreases faster than the rate of drinking it in.

Scientists say that each species feeds in different ways, so the perfect nectar sugar concentration for the highest energy intake depends on the species drinking it.

The hope is that these new insights will help researchers to better predict which types of nectar bumblebees and other pollinators prefer, and the kinds of flowers and plants they are likely to visit. This informs planters in producing the most appealing flowers for better pollination and higher crop yields.

This research was funded by the Biotechnology and Biological Sciences Research Council.