Honeybees in the US may have just experienced their most severe die-off on record, and we don’t know exactly why.
“As of right now, it does look like this is going to be the largest colony loss that we’ve experienced in at least the last 25 years – and probably in US history,” says at Cornell University, New York.
Beekeepers in the US often experience some colony losses over the winter – for instance, were lost between October 2023 and April 2024. But the scale of die-offs this winter seems to be far higher. According to by , a non-profit that supports US beekeepers, about 55 per cent of colonies – an estimated 1.6 million – have been lost.
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The losses seem to have been particularly severe for commercial beekeepers, those with 500 or more colonies. Project Apis m.’s figures suggest about 62 per cent of commercial hives have been lost, whereas losses for hobbyists who keep just a handful of colonies are about 51 per cent.
That is a surprise, says at Texas A&M University. “Commercial beekeepers are very knowledgeable; their livelihoods depend on keeping the bees alive,” she says. “So that group typically experiences lower losses than hobbyists.”
Project Apis m. estimates US beekeepers will lose at least $600 million because of the die-offs. But the full economic cost will be far greater, because beekeepers hire out their colonies to help US farmers pollinate important crops, including almonds, blueberries and apples. “Globally, honeybees are responsible for about half of crop pollination,” says McArt.
There is also a possibility the die-off is affecting other pollinating insects and not just honeybees, says Rangel. That might lead to broader impacts on ecosystems across North America. “I think of honeybees as a little like the canary in the coal mine,” she says.
However, the idea honeybees can tell us about wider ecological impacts is complicated, because they are a domesticated and non-native species with unusual biology. In most of North America’s native bee species, only the queen survives the winter to reproduce the following year. Honeybees are different – the entire colony overwinters, says at Michigan State University. “The colony produces a special cohort of bees that have extra fat storage in their bodies to survive through the winter months when there’s no incoming food,” she says.
The dead bees seem to have belonged to this special cohort, which could help to narrow down the possible causes of the die-off, says Milbrath. For instance, many US honeybee colonies are infected with potentially lethal varroa mites, that feed on the bees’ internal fluids. The mite population in the hive usually peaks in autumn, when the winter bees are beginning to emerge, so they could be partly responsible for the winter losses, says Milbrath.
But this idea doesn’t rule out other factors, such as pesticides, which bees can bring into the hive while foraging in summer months. Winter bees may die when they consume pesticide-tainted food stores later in the season, says Milbrath.
McArt and his colleagues at Cornell are currently analysing samples from some of the affected colonies to look for signs of pesticide exposure. “There are other labs looking into other angles – whether a new pathogen has cropped up, for instance,” he says. “We do have some data, but I don’t have any results yet. We’re working on it.”
