Unusually Hot Spring Threw Plants, Pollinators Out of Sync in Europe

Butterflies hatched early with the heat, but their flowers hadn’t opened yet. Bees are under pressure, too. 'You can see the climate change.'

A European honeybee (Apis mellifera) is dusted in pollen on a purple mallow in Gobelsburg, Austria, in 2017. Credit: Bob Berwyn
The European Commission formally recognized the threats to bees and other pollinators in a proposal adopted June 1. Its website lists climate change as one driver of pollinators' decline. Credit: Bob Berwyn

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VIENNA, AUSTRIA — In a patch of scruffy prairie near Vienna, marbled white butterflies hover near clusters of unopened globe thistles. They uncurl their long proboscises to probe the spiky buds—without success. It’ll be a couple more weeks before the flowers open, but some of the butterflies may not survive that long if they don’t find something else to eat.

Two months of unusually high spring temperatures in Europe have thrown the ecosystem in this urban wilderness meadow out of whack, says butterfly expert Marion Jaros. The warm temperatures accelerated the hatch of many butterflies and other pollinating species, but the flowers they depend on for nectar are not responding in sync.

“Here, too, you can see climate change,” Jaros says, as a hot, dry wind rustles the tall grass, dried to golden straw a month sooner than usual. Important pollinator species are being affected across Europe, she adds.


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“In a nearby forested wetland area, scientists documented how one of our most beautiful and rare butterflies, the Osterluzeifalter, is affected by global warming,” Jaros said. “The research showed that the sharp rise in spring temperatures in Austria makes the butterflies emerge from their cocoons several weeks before their host plants have any nectar or pollen to offer.”

That’s also a problem for the plants that rely on butterflies and other insects for pollination. In some cases, the flowers are opening too far ahead of their pollinators; in others, the pollinators, like Jaros’s butterflies, arrive too early. 

This year’s spring heat is giving scientists a chance to study those complex interactions in real time, said University of East Anglia ecologist Anthony Davy.

A Jersey tiger day-flying moth (Euplagia quadripunctaria) rests on a wildflower in northeastern Austria. Credit: Bob Berwyn
A Jersey tiger day-flying moth rests on a wildflower in northeastern Austria. Credit: Bob Berwyn

An alarming 2017 study showing significant insect losses across a big network of protected areas in Germany rang an alarm bell, and scientists have stepped up monitoring in response, Davy said. “Climate disruption causing a widespread loss of nectar and pollen is plausible as a significant factor in the alarming decline of pollinators in Europe,” he said. “I think it’s very likely it’s a factor.”

These Ecosystem Changes Can Happen Fast

The challenge is distinguishing between the effects of year-to-year variability and climate change, Davy said.

One way of doing that is by looking at long-term trends with very specific examples, like a rare orchid he studies in the United Kingdom. By scouring flower and climate records going back more than 350 years, the scientists determined that climate change had disrupted the delicately timed sequence of flowering and pollination.

By the time many of the orchids are blooming now, the bees aren’t as interested. “Continuing warming will increase the frequency of years in which this rare orchid suffers complete reproductive failure,” the scientists concluded.

“It’s a very specific example of what can happen,” Davy said. “It indicates the potential for things to go really badly, and things are moving quite fast.”

Insects like this bee beetle (Trichius fasciatus) are important pollinators for woodland wild plants, which in turn provide important sources of food for other animals. Credit: Bob Berwyn
Beetles like this one are important pollinators for woodland wild plants, which in turn provide important sources of food, such as berries, for other animals. Credit: Bob Berwyn

Adding to the massive impacts from development, agriculture and pesticide use, climate change impacts could drive many species toward extinction, he said.

New EU Proposal Aims to Protect Pollinators

The global warming threat to pollinators was formally recognized by the European Commission in a proposal adopted on June 1 to try to stop the pollinator decline. For some groups of insects, including dragonflies, the Commission’s website shows climate change impacts as the biggest threat.

The 2017 study from Germany on insect losses hints at the scope of the problem, showing that the number of flying insects had declined 75 percent over a quarter of a century in the areas studied. Its findings lent urgency to the European Commission’s pollinator protection project.

Along with a proposed ban on the pesticide neonicotinoid, the Commission’s proposal calls for conservation actions like preserving and restoring natural habitat for pollinators.

Large connected patches of habitat can help pollinating insects migrate to areas with better conditions, but if those routes are cut off, local populations could blink out. While a few insect species, like monarch butterflies, make spectacular long-distance migrations, many others live their entire life cycles within a few square miles.

A common blue butterfly lands on a wildflower in the Vienna butterfly meadow, part of an urban wilderness area that helps preserve regional pollinator biodiversity. Credit: Bob Berwyn
A common blue butterfly lands in the Vienna butterfly meadow, part of an urban wilderness area that helps preserve regional pollinator biodiversity. The meadow, affected by drought this year, has flowers at different stages. Some bloomed much earlier than usual, while other lagged. Credit: Bob Berwyn

About 80 percent of all wild plants rely on insect pollinators, and the majority of food crops benefit from them, according to the European Commission report. But 10 percent of pollinating insects are “on the verge of extinction,” and a third of all butterfly and bee species are declining, the report states. It warns that the loss of pollinators would cost billions of dollars and could threaten food security.

It’s pretty clear that bumblebees will take a big global warming hit, University of Sussex ecologist Dave Goulson said.

“Many bumblebee populations are small and stressed already, and their habitat is really fragmented. That’s going to greatly hamper their ability to shift in response to global warming,” Goulson said. “We know it’s going to get a lot warmer. They are not going to be able to deal with what’s coming.”

Several studies have shown how bumblebee ranges are shrinking from the south, but not expanding to the north, which suggests they will be squeezed out of many areas, he added.

Global projections suggest insects in tropical areas will take the biggest hit because temperatures will start exceeding livable thresholds for some species.

U.S. Ecosystems Are Feeling the Heat, Too

In the United States, University of Maryland biologist David Inouye is starting another summer of field research at the Rocky Mountain Biological Lab near Crested Butte, Colorado, where he has tracked the effects of climate change on local ecosystems since 1973. The scientists are documenting year-to-year changes in about 100 species.

Drought conditions have prevailed in the Southwest since about 1999, and some of the ecosystem fabric woven together by dynamic biological interactions among species is starting to fray. Just like the recent European studies, research from the Rocky Mountain lab also shows that global warming is disrupting the timing of some key plant and pollinator species.

Last winter was brutally dry in the West Elk Mountains of Colorado, and Inouye said he can already see the effects from the deck of the research station cabin. There are fewer wildflowers, and more hummingbirds are using the feeders because there is less food for them in the fields and forest glades.

“When we have a very early snowmelt, it means that the plants start growing early, and that means there aren’t as many flowers for pollinators,” Inouye said. Frequently in recent years, early snowmelt has been followed by late frost, which then freezes the flowers. Other plant species fail to grow and bloom if there’s not enough winter moisture.

“As we’re seeing more extremes in the weather, like droughts in the West, these declines in flowers that affect pollinators will become more common,” he said.

Climate Change Overlays Everything

It’s not far-fetched to think that the regionally documented breakdowns of pollinator-plant relationships could coalesce into a national pollinator emergency for the U.S., putting at risk $3 billion worth of pollination services, said Scott Black, executive director of the Xerces Society for Invertebrate Conservation, a science-based advocacy group.

“Climate change is this big monster that’s overlaying everything. It’s integrated into everything else,” he said. “You can’t talk about conservation without talking about the future, and climate change is going to affect suitable habitat, disease spread and invasive species.”

Avoiding the global warming train wreck for pollinators requires making sure there is enough connected habitat enabling insects populations to migrate with climate change, Black said. That could include assisted migration, with a series of way stations, as are being created for monarch butterflies, he added. The Xerces Society is working with landowners in California’s agriculturally vital San Joaquin Valley to plant 20 miles of hedgerows with a variety of native vegetation to help connect habitat across big tracts of the Central Valley landscape.

In a chapter of a recent book on climate change and pollinators, he points out that there will be insect winners and losers. For example, some species will benefit from global warming, like native tree-killing beetles are thriving in North America’s warming climate. 

Many insects can adapt to a different food source if one particular plant is not available, and plants can adapt to new pollinators, he said. “But at some point, even redundant systems become so simplified that they crack and start to break down.”

“We haven’t reached that tipping point,” he said, “but we’re heading toward it.”