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Bumblebees, essential pollinators, are hardy insects that enjoy the cold. What will global heating mean for their survival?

Bumblebees, essential pollinators, are hardy insects that enjoy the cold. What will global heating mean for their survival?

BUMBLEBEES LIKE THE COLD. They sport little hairy sweaters to keep warm, set out in thick bands of alternating black and yellow. They’re adorable little fuzzballs, buzzing around fields in search of pollen to stash in tiny baskets on their hind legs — no kidding — merrily fertilizing plants as they go. I think of them as chubby, bundled-up Cupids, flitting from flower to flower, hooking them up for botanical sex.

It stands to reason that they have an insulating layer. Although the very first bumblebees evolved about 130 million years ago, the spread of today’s 265 Bombus species began in the cool mountains of central Asia about 30 million years ago, when the world was chillier. Even today, bumblebees gravitate to cooler parts of the world, including Ellesmere Island in Nunavut. Over winter, their queens hibernate in burrows in the ground until the thaw tempts them to emerge and start new colonies.

A few years ago, nature-lovers and scientists realized that wild bumblebees all over the world are in sharp decline, along with many other pollinators. Some bumblebee species have actually become endangered. But why? Is it pesticides? The spread of agriculture? Apian viruses? The puzzle captured the imagination of Peter Soroye, a PHD student at the University of Ottawa, who’s been known to tweet that bumblebees are the most adorable insects alive.

So he started to think about their love of the cold. And that, naturally enough, led him to think about heat. What if higher temperatures, caused by the mounting carbon load in the atmosphere from burning fossil fuels, had something to do with the death of the bumblebees?

Typically, when climate scientists talk about temperature changes, they look at how much temperatures will increase on average. The discussion about 1.5 degrees, for example, refers to the maximum global average temperature rise, in Celsius, that scientists think the world can withstand before we’re hooped. But averages mask regional differences. And, Soroye reasoned, they mask spikes.

He and his two co-authors began with the numbers. Exactly how many bumblebees are there today compared with years past? And where? It turns out that because bumblebees are so adored, people in Europe and North America have been counting them for a long time.

Soroye examined records going back to 1901, capturing more than half a million sightings of 66 bumblebee species pinpointed to a specific geographic spot. Then he developed what he called a baseline of bumblebee sightings from 1901 to 1975. After that, he compared the baseline with records spanning 2000 to 2014.

That part was shocking enough. North American bumblebee sightings had dropped by 46 per cent and those in Europe, by 17 per cent. But then Soroye looked at temperature spikes. What if those weird days of high temperature simply pushed bumblebees past the limits within which their bodies could survive?

It turned out that the greatest declines were happening in places where temperature spikes were most frequent. Bumblebees were baking to death. Even more important, by tracking weather extremes, Soroye could accurately predict how well bumblebees were doing. And while some bumblebees were moving into new regions, those numbers were not even close to making up for where they were dying out. The heat deaths were also separate from death by pesticide or habitat destruction or pathogen.

It raises the question: What happens to plant life when nature’s Cupids vanish?

The paper that resulted from the study, published in Science in February, caused a media and scientific sensation. That’s because it speaks to the implacable math of hard physiological limits. When it gets too hot, the body stops coping. Resilience comes to a halt. It’s not just the average temperature that matters — it’s also the spikes that feed into the average.

And the broader message is that it’s not just bumblebees. These same calculations can be made, species by species, plot by plot, for mammals, reptiles, amphibians, birds and plants. It’s a whole new way of examining — and predicting — the risks of mass extinction.

Interestingly enough, Soroye remains buoyantly hopeful. Once we know what the issues are, he reckons, we can find solutions. The overarching one is to reduce the carbon load in the atmosphere by switching to renewable forms of energy.

But when it comes to bumblebees, there are some simple stop-gap measures, too. Since bumblebees are so well insulated, it follows that they need cool places to rest. I’ll be thinking bumblebees as I plan my plantings of wildflowers and shrubs. And I’ll be keeping a notebook handy, too, to chronicle my sightings of the pudgy pollinators. Who knows how those data might be used in the future?1