Bumblebees are waking up hungry and emerging from winter before flowers bloom, possibly due to climate change. It looks like they have devised a way to let plants know they are available and hungry. New research by a Swiss-led team reveals that bumblebees (Bombus terrestris) have been found to bite holes in flower leaves to make them bloom earlier. This may help both bee and plant adapt to climate changes.

The study reports how bumblebees damage the leaves of flowering plants to accelerate pollen production. Evolutionary biologist Mark Mescher of ETH Zürich (Swiss Federal Institute of Technology in Zürich) was the co-author of the study in Science on May 21. 

Mescher and his team noted that bumblebees bit chevron-shaped holes in plants but didn’t eat the leaves or carry the bits away. They pierced the leaves with their tongues, then cut holes with their mandibles. The team theorized that the bees were trying to make the plants flower earlier, since it is known that physical stress to a plant affects flowering.

Watch how the bumblebees speed up flowering in this 1:15-minute video:



Wild bumblebees need a lot of nectar and pollen in the spring when they start to establish colonies. This study indicates that bees can trigger earlier flowering in plants by biting their leaves, which will provide more food and let plants know that pollination is available.  

The team exposed pollen-starved bumblebees in mesh cages to tomato and black mustard plants that had not yet flowered. Once the bees had bitten 10 holes in the plants, they took them away. Remarkably, observation indicated that the bitten plants flowered up to 30 days earlier than unbitten plants. When the team tried to replicate the bites using razors and forceps, the plants blossomed a little under 25 days earlier, which indicates that there was a bee-specific factor at work that the scientists haven’t identified and can’t replicate. There is speculation that bee saliva may contain chemicals that stimulate the plants to flower, or that the manual cutting done by scientists was inaccurate for some reason, according to Professor Consuelo De Moraes, co-author of the study.  

The experiment was repeated outdoors, with plants that were prevented from flowering. Although the bees still bit plants, they did so less by late April when plants started to bloom. This indicates that bees bite leaves when pollen is scarce. The team noticed two other wild bumblebee species biting plants as well.  

Mescher referred to this behavior as evolutionary, ancient and widespread. It is likely also done by North American bumblebees. He stated that it is remarkable that bees are actively interacting with plants to cause them to flower earlier than they otherwise would, as if the smart bees are leaving a calling card that they are available for pollination.

Bees and flowers need each other. Bees need pollen and nectar to feed themselves, and flowers need pollination services which bees provide, so they can reproduce. Bees are behaviorally adapting to scarce food conditions as temperature change throws bee emergence and flowering out of sync. Mescher believes this mechanism can make flowers and bees more resilient to climate change. 

Since humanity depends of bee pollination for about one-third of our food, this is good news for us, too.