Scandia, Minnesota is a tidy, Midwestern rural farming community on the banks of the St. Croix River. It’s beautiful in September, when the fields are full of yellow corn, six-feet tall and ready to be harvested. But for a pair of local beekeepers, this scene is a reason for concern.

Pam Arnold and her friend Kristy Allen keep five hives each at Salt-n-Pepper Farm, where Arnold is one of the farm managers. The spot is ideal for bees—protected by trees, surrounded by flowering goldenrod and clover. And they’ve even corralled the stacks of pastel-colored bee boxes with electric fencing to keep the bears away. But beyond the bounds of the property, it’s corn as far as you can see.

Last year, on a spring afternoon, Arnold was out in her field chopping buckwheat when she saw a tractor across the road, ready to do the planting. She noticed the winds were blowing toward her property. And that’s when she started to get a bad feeling.

“So I checked on the beehives within a few hours of the corn being planted,” Arnold says. “At that point, there were piles of dead bees in front of each of our hives.”

Arnold has seen insects die after corn planting before. But this time was different. The effect on her bees was immediate—and dramatic.

“[There were] thousands of dying bees—behaving oddly, lying on their backs, flailing their legs, spinning around, trying to clean off their bodies. It was a stunning experience.”

LISTEN: “Tracing the Pesticides That Could Be Killing Bees”

Arnold’s friend Kristy Allen has seen similar things happen to her bees. Back in 2013, one of Allen’s hives got hit with a pesticide called Fipronil, which is used to keep termites away from buildings. By the time she got to the hive, more than 20,000 bees were already dead. The rest were writhing on the ground. She lost the hive. And she never found out who did it.

But Allen didn’t just take the loss in stride. She wanted whoever had sprayed the Fipronil to be held accountable. So she talked to legislators. She sat in on committee sessions. She lobbied. And four months later, there was a new law on the books.

It did two things: It made Minnesota the only state in the country to compensate beekeepers if they lost a hive due to someone else’s errant spraying. And it created a task force of scientists to investigate these acute pesticide kills. Like a police forensic unit, this team traces the chemical culprit back to its human source. They’re the Minnesota Department of Agriculture’s ‘bee team.’

When Arnold and Allen found their bees reeling after that spring corn planting, they called the bee team for help. This was on a Friday afternoon. By the next Monday, the bee team was there to investigate. To find out what happened, the investigators gathered clues. And bees. Live bees went into jars and onto ice, so any pesticides in their bodies stay preserved. Dead bees get measured by volume, which gives a sense of the overall death toll. One cup equals about 1,000 bees, which is the number you need to qualify as an “acute kill.”

“That corresponds to whether or not we can compensate,” says Jamison Scholer, an entomologist with the bee team. “It indicates a level of damage that a colony may not be able to bump back from.”

Because the effect on their bees was so dramatic, Arnold and Allen suspected a pesticide might be to blame. But before the Department of Agriculture could determine a culprit, the samples had to be analyzed.

In a lab at the Minnesota Department of Agriculture in St. Paul, Environmental Analysis Unit supervisor Yoko Johnson is doing just that. She starts by grinding up the bees and then mixing them with some liquid and salt. Then they get spun around in a centrifuge to extract any pesticides that might be present in the sample.

Yoko then turns on a machine that kind of looks like a big white microwave. It’s called a Gas Chromatography Mass Spectrometry machine. It heats the sample to 250 degrees, which turns it into a gas. Then a sticky coating on a coil inside the machine separates out all the chemicals, including any pesticides that might be present.

Finally, the machine breaks up the different chemicals and weighs them. Each one leaves behind a unique signature. And like running a set of prints against a criminal database, the offending chemical can be lined up with the Department of Agriculture’s molecular library.

Just like that, they’re able to know exactly which chemical is to blame. For Arnold and Allen, it was a pesticide called Clothianadin. In the U.S., it’s sold under the name Poncho 600.

“There are certain levels that EPA considers toxic to bees,” Allen says. “Ours was on the lower side, but it can still impact them.”

Clothianadin belongs to a class of pesticides known as neonicotinoids—a name they’ve been christened with because they’re chemically similar to nicotine. They’re used in about 95 percent of U.S corn and soy crops. Most often, they are incorporated in seed coatings to protect seeds from hungry insects while they’re in the ground. But researchers have found that the pesticides can come off as dust and drift onto other plants, like dandelions and pussy willows—plants that bees like. This is how Arnold and Allen believe their bees brought home the poison that would eventually kill them.

“[There were] thousands of dying bees—behaving oddly, lying on their backs, flailing their legs, spinning around, trying to clean off their bodies. It was a stunning experience.”

Not all of Arnold’s bees died following the pesticide hit. But she says the ones that lived haven’t been the same since.

“These bees are not defensive,” Arnold says. “They’re lackadaisical and they haven’t put up any honey.”

Meanwhile, Arnold has been watching another hive on the farm. It’s one she was tending for a friend, providing it with pollen and sugar water. Those bees weren’t out foraging on the day of the corn planting. So they actually served as a kind of control. And this hive is doing very well.

Months after the incident, there isn’t any closure for either Arnold or Allen. Their cases remain open. Pesticide investigators are continuing to dig through records, interview neighboring farmers and look at weather logs. Since 2014, when the compensation law was passed, there have been 10 investigations, including Arnold and Allen’s. To date, no one has been compensated. And while it might be poetic for Allen to be the first person to benefit from a law she helped write, she’s not holding her breath.

“If we do get compensation—awesome,” she says. “But it’s not about the dollars. It’s about the fact that this is the system we’re in. And there have been multiple days where I’m banging my head against a beehive and I’m like, ‘Why am I doing this?’ You can go into a hive and everything looks beautiful and normal, and the next day, it’s like, ‘What happened?’”

Whatever happens with Allen’s investigation, it’s already become an important data point for her as she tries to make sense of the losses. Lately, a picture has started to emerge. In 2015, her best hives were across the river in Wisconsin where it’s too hilly for industrial agriculture. The worst ones were those surrounded by corn in southern Minnesota. She admits it may not be strictly scientific, but it’s information she’ll use this year to try to give her bees their best shot at surviving.

For Arnold, moving her bees isn’t an option. This is their home. And it’s her home too.

“The privilege of living in an environment where all these things are visible to us is counterbalanced by the growing awareness that we’re watching it end,” Arnold says. “Because what’s affecting our bees is affecting the birds, the water—the entire system.”

Amidst the uncertainty, some answers are beginning to emerge. In the summer of 2015, British scientists showed that honey bee die-offs were linked to neonicotinoid seed treatments—the same stuff that Arnold and Allen suspect killed their bees. Now, similar studies are underway in the U.S. Bees pollinate 90 percent of the world’s food crops. So if the pesticides we use really are killing them off, bees might not be the only species losing out.

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This story is a production of the STEM Story Project, which is distributed by PRX and made possible with funds from the Alfred P. Sloan Foundation. Photo (top): Viv Lynch via Flickr