How microplastics threaten honeybees and our food supply

Get a honeybee near a rose or a lavender and the insect will extend its strawlike tongue to search for nectar, pollinating the flower in the process. That’s at least how it works in clean environments. But experiments show that when bees are exposed to microplastic pollution, their memory gets so muddled they may forget the scents associated with sugary rewards. As a result, pollination may fail - which is bad news for flowers and crops.

While honeybees - the most important pollinator of crops - seem particularly affected, other pollinators, such as bumble bees, suffer, too. Such insects visit flowers to forage for nectar and pollen as food for themselves and their young and then transfer the pollen from male parts of one flower to the female parts of another, fertilizing it in the process.

How do microplastics in our environment potentially harm pollination? Recent studies have shown that tiny pieces of plastics, which may originate from everyday products such as food packaging, disposable cutlery or plastic toys, can make bees more susceptible to bacteria and viruses. When, say, a plastic water bottle ends up in a ditch or in a river, it disintegrates with the help of the sun, water, and wind into ever smaller pieces, which float in the air, seep into soils, settle on vegetation. Other microplastics are made minuscule from the start - such as glitter or microbeads in body scrubs. They may get washed off from our skin into wastewater, which is then used for irrigation of crops.

Once such microplastics are ingested or inhaled by bees, they can damage their guts and get into their brains, impacting memory and learning, research has shown. They can outright kill them, too. In addition, flowers may get literally clogged up with microplastics.

“If plastic is adding to all the stressors that pollinators are facing already, I think we really might be in a tricky position,” said Thomas Cherico Wanger-Guerrero, an agroecologist at Agroscope, Switzerland’s federal research center for agriculture. According to the Environmental Protection Agency, pesticides, habitat changes and new emerging diseases have all been suggested as causes of colony collapse, in which bees disappear and hives die off.

Microplastics are tiny: smaller than 0.2 inches in length or diameter. Some are minuscule fibers, some are spheres, and some are tubelike. They are made of various chemicals: from polystyrene (think plastic foam cups) and polyethylene (found in cosmetics) to polyethylene terephthalate (PET), used in synthetic textiles, for example.

Every year, about 52 million tons of large plastics slip into the environment, many breaking down into minuscule pieces. By now, research has found microplastics everywhere: in soils, in our food, in the air and even in human brains. “We are essentially breathing plastic,” Wanger-Guerrero said.

And so, it seems, are bees. “Bees can accumulate microplastics from many sources like air, water, soil and also flowers,” said David Baracchi, a behavioral ecologist at the University of Florence in Italy. In 2021, a study conducted in Denmark detected 13 types of microplastics on honeybees’ bodies. Since then, other studies have confirmed that bees are often covered in tiny plastics, which stick to their wings, their heads, their abdomens.

Bees can swallow microplastics with nectar, too, so that they accumulate in their guts. The consequences may be serious. A 2024 study by Baracchi and his colleagues found that polystyrene and another type of microplastic, polymethyl methacrylate, mixed together, may kill bees. The scientists separated bees into small cages and fed some of the insects a sucrose solution combined with microplastics, at a concentration that can be found in the environment (the control groups dined on pure sucrose). Each day, the researchers counted the number of dead bees at the bottom of the cage and found that the microplastics increased the mortality of honeybees by as much as 25 percent.

While not all studies show that microplastics kill bees, Baracchi said it may depend on the type of polymer - even if the insects do survive, their health may suffer. They may, for instance, lose appetite and weight. They may lose their hair and become darker in color. Research has also found that tiny particles of polystyrene alter the expression of honeybee genes related to their immune response.

Bees exposed to microplastics may be more vulnerable. The bacteria Hafnia alvei can cause severe infection in bees (it can also cause disease in cows, chickens, snails and, in rare cases, humans, too). Recent experiments showed that when bees are fed a sugary syrup spiked with microscopic fragments of polystyrene, the insects are much more susceptible to the microbe and have a mortality rate five times higher.

In other studies, honeybees fed microplastics developed worse infections with a pathogen that has been linked with colony collapse. Microplastics can also reach honeybee brains and may affect their thinking. Baracchi and colleagues fed bees fluorescent microplastics for three days, and with powerful microscopes observed how these polymers migrated into the insects’ brains. They could see them, he said, because the tiny plastics literally lit up in the brain. When Baracchi and his colleagues trained honeybees to associate certain scents with a reward, “like Pavlov’s dogs,” he said, the bees that had ingested microplastics forgot their lessons faster than did unaffected insects. It took a mere 24 hours for the bees to be “no longer able to recall” what they had learned, Baracchi said. Out in the real world, he said, that could mean forgetting the way home or where to find nectar.

Microplastic-laden bees can also mean microplastic-laden honey. When Turkish scientists tested samples of honey, they discovered that a vast majority contained microplastics, with single-flower honeys the most affected. In Germany, commercial honey contained almost 300 pieces of microplastics per pound - or about five pieces in each teaspoon.

Yet microplastic pollution doesn’t just harm animals and end up on our tables - it also impacts flowers. A 2024 study on Andean yellow monkey flowers, alpine plants with small, golden flowers, showed that tiny pieces of polypropylene can jam the stigma, the sticky part of the flower that catches pollen. A bee can “transport plastic to the flower and put it on the stigma,” said Gastón Carvallo, an ecologist at the Pontifical Catholic University of Valparaíso, Chile, and the study’s lead author. Then, he said, the microplastics “clog the stigma for pollen’s arrival” so the plant can’t be effectively pollinated - and the seeds won’t form.

Research shows that when tomatoes are grown in soil polluted with tiny pieces of PET and polyvinyl chloride, which may come from plastic greenhouse films, for example, they develop 28 percent fewer flowers, compared with plants grown in clean soil. Similar effects have been found in white mustard (the plant behind table mustard).

Carvallo said many plants struggle to grow in microplastic-polluted soil. “They have small leaves; they are smaller in size,” he said.

We are only beginning to scratch the surface on how microplastics affect pollination, Baracchi said. One thing is clear, though, Wanger-Guerrero said: “The urgency to mitigate exposure of nature to plastic.” And not just in the oceans, he said, but on farms, too. After all, our food supply may depend on it.