April Showers Bring May Flowers. So Do Bumblebee Bites.

New research shows that bumblebees have the power to make plants bloom.

A bumblebee flies in search of nectar over a still flowering basil plant.

Credit: Ulrich Perrey/picture alliance via Getty Images

Humans were once thought to be the only species that made tools. We used to be the only species believed to farm. We once considered ourselves to be the only species that had sex for reasons other than reproduction. Scientists eventually identified all of those behaviors in other species, from chimpanzees to ragworms to dolphins.

Here’s another way humans are no longer unique: We are not the only species that orders food when the fridge is bare.

Go with me on this. Researchers in Zurich recently observed bumblebees doing something unexpected. When they couldn’t find enough flowers to feed the colony, the bees bit into the green leaves of plants that had not yet flowered. They weren’t eating the leaves—bumblebees consume only pollen, nectar, honey, and occasionally the poop of other bees—but they were merely pinching the leaves with their mandibles and creating little injuries to the greenery. To the scientists, it seemed like an act of frustration from the hungry bees.

But it turned out to be much more than that. The researchers designed a controlled experiment, exposing some tomato and mustard plants to bumblebee bites, while leaving a set of control plants undisturbed. They found that the bitten plants flowered dramatically earlier than the unbitten controls, as much as 30 days earlier. By biting the leaves, the bumblebees were sending a message to the plant: “I’m hungry. Where’s the flower I ordered?” And the plants responded by accelerating the flowering process.

Once they observed this phenomenon in the laboratory, the scientists started seeing it everywhere. Even on the rooftops of Zurich, bumblebees that had been deprived of nectar and pollen pinched and bit the leaves of flowering plants, prodding them to produce food.

The team recently published their findings in the journal Science, but many questions remain. For example, while several species of bumblebee were observed biting leaves (FYI, there are more than 255 species of bumblebee), honeybees don't seem to use the same trick. When a plant has not yet flowered, a honeybee just passes it by, apparently unaware that a little nip might hasten a meal’s arrival.

The human researchers also proved surprisingly inept in the bumblebee art of flower encouragement. When the scientists pinched at the leaves, trying their best to mimic the tiny injuries wrought by bumblebee mouths, the flowering process barely accelerated at all. Were they just doing it wrong? Or is there some chemical cue that the bees deliver to the plant? The answer could be quite valuable to farmers.

But the research has implications beyond apiculture and agriculture. One of the least appreciated consequences of climate change is the desynchronization of the seasonal lives of different species whose reproduction and sustenance rely on each other. Bees and flowering plants are a perfect example of this. Over millions of years, the timing of when plants flower has evolved in response to the planet’s gradually changing climate. Bees evolved with them, syncing their life cycles with the availability of pollen and nectar when they need it most. As part of that dance, the bumblebee’s special talent for accelerating flowering times is likely an adaptation that took off as a strategy to deal with small variations in weather and climate.

But what will happen when those variations aren’t small, as the climate switches to an entirely different rhythm—changing not at the slow pace of Mother Nature, but at the double-time beat of human-caused pollution? Will the bumblebees’ coping mechanism keep them in sync with the flowers, or will climate change prove too much for this time-tested food-delivery system?

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