During their search for food, most insects head specifically for the flowers that promise the highest reward. But how do they know which ones to choose? Researchers from the University of Konstanz and the University of Würzburg have now studied how bumblebees process information about their food sources.

Which strawberries on the supermarket shelf are likely to be the sweetest? Should you take the deep-red ones, those with greenish patches, or perhaps the ones with the most intense scent? To make decisions like these, we process vast amounts of information every day and draw on all our senses. We learn how to interpret different kinds of information through experience — and animals are no different. A recent study by the University of Konstanz in cooperation with the University of Würzburg investigated the decision-making behaviour of bumblebees and found that these insects take a "shortcut" in information processing if it saves them time. In this respect, their decision-making behaviour is indeed quite similar to that of humans.

Many flowers – many decisions
While foraging for their colony, bumblebees visit hundreds of flowers each day and have to decide each time which ones are likely to offer the greatest reward. "As they make so many decisions in very short periods, bumblebees are particularly well suited for studying decision-making processes", says Anna Stöckl, neuroethologist at the University of Konstanz and co-author of the study. To avoid wasting too much energy on flights with little prospect of success, it helps the insects to memorize which types of flowers previously contained nectar or pollen – and are thus likely to provide food on their next visit, too. "To remember a good source, they primarily rely on the flowers’ colours. However, they are also capable of recognizing shapes, patterns and scents", explains Stöckl. Just like people in front of the supermarket shelf, who know from experience that key criteria for choosing strawberries are colour and smell.
But how many features do bumblebees store to quickly and reliably identify a good food source? To test this, the researchers first trained the insects to associate a certain combination of traits with a reward. Artificial flowers in various colour combinations were paired with either a pattern or a shape. In one trial, for example, the bumblebees were rewarded with a sugar solution when they visited a blue, star-shaped flower, whereas a yellow, round flower contained only water. In another experimental set-up, the animals were trained with flowers whose colours were very similar (for example, yellow and orange). After several rounds, the researchers observed that the bumblebees increasingly headed to the flowers containing sugar solution. "For us, this indicated that they had memorized the flowers' features and included this information in their decision-making," says Stöckl.

Storing only essentials
Now the actual research began to determine which of the features the bumblebees are guided by: primarily shape, primarily colour or both equally? To get to the bottom of this question, the researchers mixed the already trained colours and shapes, forcing the bumblebees to choose between the learned features: For example, the star-shaped flower was now yellow, the round flower blue. The result was unmistakable: The bumblebees continued to choose the colour they had learned, not the shape, expecting to find nectar at the blue flower in most cases. In a final step, all flowers were uniformly grey, with only the shape or pattern indicating the reward.
The outcome of the experiment was clear: Only when the colours in the training phase were difficult to distinguish did the bumblebees also remember the shape, choosing the flowers with the correct shape much more frequently when the flowers were uniformly grey later on. Thus, the bumblebees adapted their decision-making strategy, i.e. what and how much they memorized, to the distinctiveness of the floral features. What especially caught the researchers’ attention was the amount of time the bumblebees needed in the training phase: "Bumblebees that were trained with flowers of clearly distinguishable colours needed significantly less time to learn which flowers they had to visit for a reward. Those trained with similar colours, in contrast, required more time to complete the learning process", says biologist and co-author Johannes Spaethe from the University of Würzburg.
Anna Stöckl explains that this strategy allows the bumblebees to conserve valuable resources: "Learning and storing only the colour probably requires less processing effort than remembering colour and shape at the same time. Only when the colours were similar did the bumblebees also learn shapes and patterns, which makes the learning process take longer. In this way, the insects consistently achieve the best possible outcome by following the principle of 'as much as necessary, as little as possible'," she concludes. The bumblebees' decision-making is, as it turns out, quite similar to that of humans: When faced with many unripe green strawberries, most people will naturally choose the red ones. But if all the strawberries on display are deep red, it becomes helpful to know what ripe strawberries smell like.

Key facts:

• Original publication: Johannes Spaethe, Selma Hutzenthaler, Alexander Dietz, Karl Gehrig, James Foster, Anna Stöckl (2026): Bees flexibly adjust decision strategies to information content in a foraging task. DOI: 10.1126/sciadv.adw9320
• Anna Stöckl is a junior professor of neurobiology and behaviour as well as the leader of an Emmy Noether research group at the University of Konstanz. She is a member of the Centre for the Advanced Study of Collective Behaviour.
• Johannes Spaethe is a biologist and research group leader at the Biocenter of the University of Würzburg.
• Funding: The project was supported by the Bavarian Academy of Sciences and Humanities, the Zukunftskolleg of the University of Konstanz and the Emmy Noether Programme of the German Research Foundation (DFG) (STO 1255/4-1).