Food & Climate
New research, which focusses on monarch butterflies, shows that they become more vulnerable even with limited temperature increases. The rising temperatures can make flower nectar less nutritious, leaving butterflies with less energy even when food appears plentiful.
It is showing that climate change can affect pollinators indirectly, by altering the resources they rely on rather than harming them outright.
Now, scientists say it may be undermining butterflies in a way that could go under the radar. The warming planet is reducing the quality of the nectar butterflies depend on to survive.
The study focusses on monarch butterflies, famous for their migration of nearly 3,000 kilometres from Canada to Mexico.
Researchers behind the study found that the warming climate doesn’t need to be extreme to cause harm. Even small temperature increases can change how flowers produce nectar, directly affecting the insects that feed on it.
“It’s not that the butterflies are being directly harmed by the heat,” said Heather Kharouba, Associate Professor of Biology at the University of Ottawa, who led the study.
“It’s that warming is making the nectar less nutritious. Even though the butterflies could eat as much as they wanted, they couldn’t make up for the lower-quality nectar”, according to the report that has seen by Food & Climate.
Resilient of monarch butterflies
Monarch butterflies have always been remarkably resilient. Every fall, these delicate orange-and-black travelers set out on a journey so improbable it borders on myth, flying some three thousand kilometers from Canadian fields all the way to Mexico’s mountain forests, their overwintering grounds, according to India today.
They’ve been weathering habitat loss, extreme weather and pesticides, but new research from the University of Ottawa suggests a new snag in their epic trek. The culprit? Nectar. Turns out, their main food source isn’t what it used to be.
During summer 2023, a team of scientists led by Heather Kharouba, Associate Professor in the Department of Biology at the University of Ottawa and University Research Chair in Global Change Ecology, set up a simple but revealing experiment. Instead of only focusing on the butterflies, they also looked at the plants the monarchs depend on during migration.
They observed that a tiny bump in temperature, just 0.6 degrees Celsius, was enough to lower the quality of the nectar these plants produced. Monarchs fed on these “warmed” blooms built up about a quarter less body fat than their counterparts.
The experiment, carried out by Katherine Peel, a MSc student, from Dr. Kharouba’s research lab, and collaborators from Environment and Climate Change Canadanorth_eastexternal link and Western Universitynorth_eastexternal link, took place at the Fletcher Wildlife Garden in Ottawanorth_eastexternal link.
The team ensured that only the plants were warmed and that the butterflies remained at regular outdoor temperatures. The results were clear: as the temperature crept up, late-season flowers produced less nectar, and what they did produce was lower in sugar.
Scientists have known for years that monarchs are in trouble, but this study uncovers a subtler risk. “We’re seeing that climate change can hit pollinators indirectly, by degrading the resources they count on,” explains Professor Kharouba. “I believe the findings are a wakeup call for anyone working to protect these butterflies and, really, for anyone planting a garden or maintaining a park as the planet heats up.”
Help monarchs by planting milkweed
Monarch butterflies embark on a marvelous migratory phenomenon. They travel between 1,200 and 2,800 miles or more from the northeast United States, and southeast Canada to the mountain forests in central Mexico, where they find the right climate conditions to hibernate from the beginning of November to mid-March. The monarch butterfly is known by scientists as Danaus plexippus, which in Greek literally means “sleepy transformation.” The name evokes the species’ ability to hibernate and metamorphize. Adult monarch butterflies possess two pairs of brilliant orange-red wings, featuring black veins and white spots along the edges. Males, who possess distinguishing black dots along the veins of their wings, are slightly bigger than females. Each adult butterfly lives only about four to five weeks.
Milkweed is the only plant on which monarchs will lay their eggs and the only source of food for baby caterpillars. But urban planning and agricultural expansion have paved and plowed over millions of acres of milkweed. Planting the right species of milkweed in a given area can help these amazing butterflies and other pollinators thrive, according to World Wild org.