A New Study Reveals Why Bumblebee Queens are Suddenly Damaging Leaves

Because insects are generally small, humans tend to underestimate their intelligence. However, from their complex social structures to learning and memory, insects, especially ants and bees, are surprisingly astute. In the most innovative ways, these tiny creatures consistently adjust to environmental changes such as earlier seasonal activity patterns and reshaping their geographic range. Increasingly, insects are adapting to climate change in ways we could never have imagined.

A recent scientific study from Switzerland (De Moraes/Mescher, 2025) has determined that leaf-damaging behavior in bumblebee queens is related to the timing of flower production as it affects nest founding. Continue reading to discover more about this behavior and its implications.

Bombus: An Overview

There are more than 250 species of bumblebees in the genus Bombus, members of the Apidae family, which contains nearly 6,000 species of bees. Bumblebees are a wide-ranging group, found everywhere except Australia, Sub-Saharan Africa, and Antarctica. They are not to be confused with their honey bee cousins. They are larger and hairier but live in much smaller colonies. Bumblebees are generalist foragers. This makes them excellent pollinators for wild plants as well as agricultural crops. The timing of flowering in these plants is critical to bumblebee survival and healthy colony growth.

Adapting to Change

Plants are responding to climate change by altering their flowering schedules, and bumblebees are adapting to these changes by altering their foraging behavior. The most recent study headed by Consuelo De Moraes and Mark Mescher of the Federal Institute of Technology in Zürich, Switzerland, focuses on queens of the species Bombus terrestris, commonly the buff-tailed bumblebee, and their leaf-damaging behavior as it relates to colony founding.

Earlier research by the team (De Moraes/Mescher, 2020) determined that B. terrestris workers exhibited leaf-damaging behavior to accelerate flowering when pollen was in short supply. The team hypothesized that the leaf-damaging behavior, in which bumblebees create a crescent-shaped hole in leaves, would be present in queens that were establishing nests before acquiring workers.

Their hypothesis was spot-on. When faced with pollen shortages, B. terrestris queens inflicted the same crescent-shaped holes in leaves as the workers. This information led the team to consider whether queens of other bumblebee species might inflict similar damage to stimulate flowering. Combing fields throughout the Swiss Alps, the researchers captured 105 queens representing 17 bumblebee species. Of the 17 species, 12 were documented to execute similar damage to the leaves. Previously, the workers of four of those 12 species, had been shown to produce the same damage.

Cuckoo Queens

Among the wild queens, five were Psithyrus. Commonly called cuckoo bumblebees, Psithyrus is a Bombus subgenus containing obligate social parasites, which rely on the resources and labor of other bumblebees. Because cuckoo bumblebees lack corbiculae (pollen baskets), they are unable to collect the pollen necessary to provision brood cells. These queens usurp existing brood cells in which to deposit their eggs. Absent the need to establish a nest, would these queens display leaf-damaging behavior?

Interestingly, three of the five cuckoo queens did display leaf-damaging behavior. However, of those three, only one produced crescent-shaped damage, while the other two created atypical damage patterns. “We did have a hypothesis that the behavior might be absent or different in cuckoo queens,” Mark Mescher says. Because the sample was small, “It’s hard to draw conclusions, but it would be nice to study the effects of damage by those species on flowering time,” he muses.

Methods

For their research, De Moraes and Mescher relied on commercially procured unmated B. terrestris queens from Belgium. They also captured wild bumblebee queens from different areas and elevations across Switzerland. As noted earlier, the wild queens represented 17 bumblebee species. The commercial and wild queens were placed in small climate/light-controlled chambers and deprived of nectar for three days. Afterward, the queens had unlimited access to nectar for two weeks. Pollen was provided once per week during that time. Black mustard (Brassica nigra) and tomato (Solanum lycopersicum) plants were then introduced. Whether the queens received a mustard plant or a tomato plant was based solely on plant availability.

Once the plants were placed in the chamber, queens no longer had access to a pollen source, mimicking pollen deprivation. In response to the lack of pollen, the queens, like the workers before them, damaged the plant’s leaves. Consisting of crescent-shaped holes, the damage did cause the plants to flower earlier. A control group, in which the scientists created their own crescent-shaped holes, flowered earlier, but at a slightly lower rate.

Conclusions

The data produced and collected in the De Moraes/Mescher study suggests that leaf-damaging behavior is a phenological adaptation across the Bombus genus. Because the timing of flowering in keystone plants is crucial to the health and stability of the colony, bumblebees have adapted to the out-of-sync rhythms of nature with this leaf-damaging behavior that accelerates flowering so that it coincides with colony establishment.

“The leaf-damaging behavior is almost certainly not an evolutionary adaptation,” explains Mescher, which implies a long-term genetic change. “However, we have speculated that it might help to maintain the synchrony between bees and plants, as it provides a route for direct transfer of information between them.”

The Zürich team is eager to expand its research, including the new world bumblebees in North America. “We would definitely like to confirm that the behavior is present in species from other regions of the world,” says Mescher.

Read the complete study at nature.com.