Big Bumblebees Memorize Locations of the Most Rewarding Flowers

They perform learning flights to study their surroundings.

large bumblebee on flower
Bumblebees decide how much effort to put into remember flowers. pskeltonphoto / Getty Images

Sometimes size matters. Bigger bumblebees spend time learning the locations of the most nectar-rich flowers, so they can easily find them again, new research finds. In contrast, smaller bees aren’t quite as picky.

After drinking from a flower, bumblebees decide if it’s worth visiting again. Then they perform what are known as learning flights to study the location around the flowers.

“If the flower is rich in nectar, a bee will be very keen to return and therefore invest in learning its location,” study co-author Natalie Hempel de Ibarra, associate professor at the University of Exeter's Centre for Research in Animal Behaviour, tells Treehugger.

Bumblebees will slowly fly around the flower, then fly away from it, looking back at its location. It will memorize the flower and the views all around it. On its next trip, the bee matches what it sees with the views it already memorized. This takes it back to the flower’s location.

“We have found that larger-sized bumblebee foragers are not only more likely to perform a learning flight when they find a rich flower as compared to a low-rewarding flower, but also to hover around the flower for longer. This in turn allows them to look back more at the flower and to memorise it better,” Hempel de Ibarra says.

“This investment in the learning flight pays off during subsequent foraging flights where the bee can shorten its travel time and go directly to the locations of the best-rewarding flowers.”

Smaller bumblebees do the same thing but aren’t as choosy in their flower selection.

“They also conduct learning flights when departing from a flower on which they obtained a nectar reward,” Hempel de Ibarra says.

“We find that in contrast to the large bees they readily accept lower and higher rewards and are less selective when investing in the learning flight. They spread their efforts more evenly.”

Watching Bees at Work

For the study, researchers set up an experiment in a greenhouse where they could watch captive bees visit artificial flowers containing varying concentrations of sugar solutions. A downward-facing camera captured the bees’ learning flights. The recordings included the bees, the flowers, and cylinders that marked the flowers’ positions. 

The flowers had sugar solutions ranging from 10% to 50% sucrose. When the concentration was greater, the larger bees spent more time circling the flowers and making learning flights. When the concentration was smaller, the length of time the bees spent looking at the flower and flying around it tended to drop.

Smaller bees spent the same amount of effort learning where the flowers were, no matter whether the concentration of sucrose was low or high.

The contrast likely reflects the different roles of the bees in their colonies, the researchers said.

“Large bumblebees are able to carry larger loads and explore further from the nest than smaller ones. Small ones with a smaller flight range and carrying capacity cannot afford to be as selective and so accept a wider range of flowers,” the researchers concluded in the study, published in the journal Current Biology.

Small bees are often involved with more tasks inside the nest, only going out to forage if necessary when food supplies are running low, says Hempel de Ibarra.

Benefits of Bees of All Sizes

Having both large and small bees foraging means they cover more ground and serve different purposes.

“Big bees can cover a larger area and find higher-rewarding flowers further away. Investing in flower learning and using its navigational capabilities a bee can identify the most effective travel route for its foraging trips,” says Hempel de Ibarra. 

“Smaller bees, however, do not travel far away, and they should focus on the area closer to the nest. They can return to the nest more easily without having to invest as much in navigation. Discriminating less between flower rewards, allows smaller bees to fill up the crop more quickly.”

Bumblebees aren’t the only insects that perform these learning trips. Honeybees and wasps also make learning flights and ants are known to perform learning walks.

“Learning flights are an important behaviour that is displayed by each individual forager bee,” says Hempel de Ibarra. “Understanding them can tell us a little more about which flowers bees like to visit.”

View Article Sources
  1. Frasnelli, Elisa, et al. "Small and Large Bumblebees Invest Differently when Learning about Flowers." Current Biology, 2020, doi:10.1016/j.cub.2020.11.062