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Published March 15, 2022
When a regular listener of “CrowdScience” posed the question “How high can insects fly?,” podcast host Alex Lathbridge went looking for answers from a number of sources, including a University of Wyoming faculty member.
Michael Dillon, a professor in the UW Department of Zoology and Physiology, provided some insight -- specifically, about bumblebees.
Dillon was a recent guest on the BBC World Service podcast and discussed how alpine bumblebees he witnessed in the mountains of Sichuan, China, can fly to heights greater than Mount Everest.
The producers of “CrowdScience” found Dillon through his previous research papers on the subject as well as a Saturday U talk he gave at the Jackson Wild Festival in 2016. Dillon says he conducted a Zoom interview with the show’s producer Feb. 7 and then did the taping for the show Feb. 16. The interview went live as a podcast episode March 7.
Turns out, Dillon once had the same question long before the “CrowdScience” listener posed his.
“We found in the literature that there are records of these animals up above 5,000 meters or 5,500 meters in western China. And we thought ‘That’s crazy.’ Somebody collected these that high,” Dillon said. “So, we wanted to ask ‘If we find them that high, is there some place that they can’t make it? And is there a limit to how high these things could go?’”
Variables to consider at high altitudes include low temperatures, which challenge the bees’ survival and take-off for flight; low oxygen, which challenges the bees’ metabolism; and thin air, which challenges their ability to fly, according to Dillon.
Ever the scientist, Dillon said the physiology of bumblebees provides some key answers as to how these insects have the ability to fly at such great heights.
“Bumblebees are special. They actually have huge, huge flight muscles. The entire core of their body is filled with flight muscles. And those muscles are really inefficient,” Dillon explained. “And, so, they’re super active. But most of what they do doesn’t go into useful work. Instead, it generates heat. These bumblebees heat up their bodies to temperatures even hotter than you and I.”
While the bees take off with core body temperatures of about 35 degrees Celsius, that temperature increases to 40 to 45 degrees Celsius when the bees are in full flight, he said.
Lathbridge wanted to know whether low oxygen levels at high altitudes are the same for insects as they are for a long-distance runner training in the mountains as opposed to at sea level. Dillon said there are similarities, but it’s to an extreme for the bees.
“To put it into perspective, if you look at it per gram of (body) tissue, a flying insect is using oxygen at a rate roughly 100 times faster than, let’s say, Usain Bolt running a 100-meter dash,” Dillon said, referring to the Jamaican sprinter who holds world records in the 100- and 200-meter sprints and won eight Olympic gold medals. “And then, to do that in a place where there’s half or less the amount of oxygen available makes for a pretty tough challenge.”
At one point, Lathbridge cracked that Dillon is probably not all that impressed with Olympic athletes compared to bumblebees. Of the bees, Dillon responded, “They are Olympians of the insect world, for sure.”
The podcast host also inquired as to whether these bees fly in lower air density similar to passenger airplanes. It turns out there is quite a bit of difference.
“If you are in a plane, all of the speed is being supplied by big jet engines that make that plane move quickly through the air, which means that lots of air flows over those wings per unit time, which means those wings can deflect that air downward and keep that plane aloft,” Dillon explained. “For a flying insect, all of the movement of air has to come from their moving of their wings. So, if you have reduced air density, that’s a more challenging problem because there’s fewer molecules around to push down. So, they have to change the motion of their wings somehow to allow them to continue to push enough air down per unit time to keep themselves up.”
Dillon went high into the mountains of western China in 2004-05. There, he and other researchers used specially designed boxes, essentially flight chambers built out of thick plexiglass with rubber gaskets, to test the flight limits of bumblebees.
“We hooked them (flight chambers) up to a hand pump,” Dillon said. “And, with that pump, we can either add air into the chamber and make it as if the animals are moving to lower elevations, or we can take air out of the chamber and make it seem as if the animals are moving to higher elevations.”
Dillon and others pumped air out of the box in 500-meter increments until the bees “failed,” or just stopped flying. Audio and video of the bees also were conducted.
“The biggest surprise for us is that, when we measured a whole bunch of these bees, most of them wouldn’t fail until above 8,000 meters. And a couple of them flew over 9,000 meters,” he said. “Everest is at 8,848 meters elevation. So, these bees are capable of flying over Everest despite the reduced oxygen.
“Bees are essentially nectar tankers. Bumblebees, we know in particular, can double their size when they tank up on nectar and pollen,” Dillon continued. “And, so, this flight capability is probably more about their ability to lift weights than it is their ability to fly above the top of Everest.”
“It was like flying to the top of Everest and adding the Eiffel Tower on top of it,” Lathbridge commented.
To listen to the podcast, go to www.bbc.co.uk/sounds/play/w3ct1prv.