Part of a wide range of pollinating insects, shrinking butterflies due to rising temperatures could have drastic consequences for agriculture
In the early 1970s, meteorologist Edward Lorenz placed the flight of a butterfly at the metaphorical heart of chaos theory – asking the question, could the simple flapping of the insect’s wings influence the trajectory of a tornado a few days later?
Known as the butterfly effect, the phenomenon is now used to describe how even the smallest disturbances could have dramatic consequences across an entire world.
Now, a group of British Columbia scientists have discovered that an increasingly unstable global climate is pushing the tiny insect away.
Published in the journal Ecological Entomology, the University of British Columbia (UBC) study found that the warmer the planet, the smaller and more lethargic butterflies become.
“The prediction is that with warmer temperatures, we should actually see an overall decrease in insect body size, like everywhere in the world. Do we see that? It’s a very large question,” said Michelle Tseng, an assistant professor of botany and zoology at UBC and lead on the study.
“There are 10 million species of insects. So we’re just trying to tackle it a little at a time, trying to put the pieces of the puzzle together.
Some of these patches have already appeared, with previous studies showing a range of species – from the largest bumblebees and moths to some wasps – shrinking under warming conditions.
Tseng, for his part, has previously used historical museum collections to show that climate change is leading to a decline in beetles across British Columbia. Much of the effect is due to temperature changes.
Since the Industrial Revolution, humans have released vast amounts of greenhouse gases into the atmosphere, pushing average global temperatures up by just over 1.1 Celsius.
At northern latitudes, however, communities in countries like Canada, Russia and Norway have warmed about three degrees Celsius since 1979: four times faster than the rest of the planet over the same period, according to scientists.
The confluence of a changing climate and loss of habitat for pollinators has prompted some to warn of an impending “insect apocalypse”.
In a global study conducted earlier this year, a team of British scientists analyzed three-quarters of a million records for nearly 20,000 insect species. For some parts of the world, they found that climate change and intensive agriculture are reshaping the insect world, in some places already halving insect abundance.
How to deploy a butterfly backpack
To measure the effects of temperature on insect development, UBC researchers grew butterflies of varying sizes in the lab.
Those grown at 30°C – what Tseng says resembles a prolonged heat wave – were found to be 11% smaller than those grown at 18°C, average historical summer conditions in British Columbia.
They found that the higher the temperature, the smaller the butterfly. Beyond 32 C, the butterflies die.
Next, the researchers set out to see how the little butterflies behaved in flight. But due to strained supply chains during the pandemic, materials to run the experiment were hard to come by.
So Tseng and his graduate student Erez Büyükyilmaz constructed a “butterfly backpack” from jewelry wire and non-toxic glue. With this, they attached the butterflies to a specialized tool called a flight mill. Resembling a miniature inverted windmill, the whirlwind-like machine measures the distance and speed at which a butterfly flies.
“Insects really lend themselves to these kinds of experiments because you can chill them in the refrigerator and then they sort of sleep,” Tseng said.
When tested, the smallest lab-grown butterflies were found to fly 85% farther and at a rate 5% slower than larger individuals.
None of this was particularly surprising, Tseng said, because previous research has shown that increasing temperatures lead to decreased flight distance in migrating monarch butterflies.
But many questions remained, the main one being whether laboratory experiments could continue in nature.
A pollinator running out of pollen?
In the summer of 2021, Tseng and Büyükyilmaz set out to collect wild specimens around the university and parts of Vancouver’s west side. In the end, they attracted 100 cabbage white butterflies, a species native to the Mediterranean but now spreading across much of the planet.
“Very interestingly, the size range we saw in the lab was exactly the same as what we found in nature,” Tseng said.
In a finding that could echo around the world of agriculture and eventually land on your grocery store shelf, small wild-caught butterflies collected 15% less pollen on their faces than larger butterflies.
In other words, the hotter it is, the smaller the butterfly; the smaller the butterfly, the fewer plants it visits.
“Are we going to see plants produce fewer seeds and less fruit because they’re running out of pollen?” It’s a possibility,” Tseng said.
The consequences could be devastating for agriculture. About 75% of all crops worldwide are pollinated by insects, the researcher said.
The world’s butterflies and bees are particularly essential to a variety of fruit crops, cocoa beans, nuts and avocados.
Previous research indicates that pollinator declines could lead to a drop in agricultural production of at least 5% in high-income countries, although some have speculated that this may already have reached 10%.
In British Columbia, most fruit crops are pollinated by honey bees, which face their own set of threats from climate change. But Tseng says increasing the number of bees around an orchard or blueberry field will never compensate for the wide range of natural pollinators.
“Different insects actually like to work at different times,” she said. “Honey bees, for example, don’t really like rain or rain, but other bees don’t care.”
Tseng added that “butterflies may not be the ones carrying the most pollen, but you definitely don’t want to lose the pollinator diversity you have in your fields.”
The researcher is quick to say that the single study does not conclusively establish that butterflies are bound to get smaller under warming conditions. Instead, she said it should serve as a wake-up call for farmers and anyone with a backyard or community garden.
“Maybe that means we might need to order another colony of bees or, or maybe that means we need to plant more pollinator-friendly plants – not just in agricultural areas, but like in urban gardens just to make life a little easier for these little bugs we depend on,” she said.
The best flowers will depend on where you are in British Columbia. Tseng suggests asking a local garden center for drought-tolerant native species that can serve as a stopping point for local pollinators.
“Insects are extremely important in many different ecosystems,” she said. “They’re sort of nature’s unsung heroes.”
