Higher temperatures may help some bumble bee species, especially those nesting underground, but periods of extreme heat can still threaten their survival, according to research announced on May 6. The study focused on bumble bee populations in the southeastern United States and found that while some colonies adapt well to warmer conditions, extreme heat events could contribute to population declines.
Researchers say this topic is important because bumble bees are major pollinators for agricultural and natural systems. Changes in their populations can have wide-ranging effects on ecosystems and food production.
“A lot of research on how higher temperatures affect living things has been done on individual animals,” said Clint Penick, corresponding author of the paper and assistant professor of insect ecology at Auburn University. “But when it comes to social animals, such as ants and bumble bees, you have to look at the entire society.”
Elsa Youngsteadt, co-author of the paper and associate professor of applied ecology at North Carolina State University, said, “We previously found that individual bumble bees reach stressfully hot body temperatures while foraging on warmer days. But it’s important to understand how that fits into the big picture for the entire colony. How do higher temperatures affect the nest, where the queen bee lives and where the next generation of bees is developing?”
The study examined both underground and aboveground nests by simulating conditions in lab settings and monitoring bee behavior under different temperature scenarios. Researchers also observed pollinator activity on cucumber flowers across several states from Georgia to Michigan. Results showed that underground nests are better insulated from heat, allowing workers to spend more time foraging rather than incubating brood. In contrast, aboveground nests require more energy from workers to keep cool during hot periods.
Youngsteadt explained that while most hours of increased temperature may not harm colonies directly, there are limits: “In Georgia…above-ground nests only experience about 9 hours per year where the nest gets so hot that fanning doesn’t help anymore. But in a warmer climate, that could go up to nearly 200 hours per year.” These few damaging hours could have serious effects if larvae die or develop abnormally.
Penick added that improving survival rates may depend on practical steps: “One take-away from this is that we need to find ways to keep above-ground nest boxes cooler in order to improve bumble bee survival in agricultural settings.” The researchers suggest planting native flowering plants near homes or protecting forested land as additional ways people can support bee populations.
The findings were published April 27 in the Journal of Animal Ecology.
