Skip to navigation | Skip to content

Bumblebees master high-altitude flight

alpine bee

Bees at high altitudes face enormous challenges (Source: M.E. Dillon)

Bee heights The humble bumblebee has the capacity to fly higher than Mount Everest, a new study has found.

But, rather than fly this high, bees probably use this extra capacity to escape predators and carry heavy loads of nectars when they are foraging in alpine areas, says ecologist Assistant Professor Michael Dillon of the University of Wyoming.

His findings are reported today in the Royal Society journal Biology Letters.

Bumblebees are commonly considered poor fliers and yet they regularly forage on flowers in high alpine areas.

"The highest record for a bumblebee is just over 5600 metres and that's in the Himalayas," says Dillon.

But flying at high altitudes presents bees with a number of challenges.

For a start there is reduced air density and this makes it hard to produce lift.

"If you have fewer molecules around, it's harder to push enough molecules down per unit time to offset your body weight, which is essentially what you're doing when you're flying."

Also, there is less oxygen at high altitudes and a flying bumblebee needs 15 to 20 times more oxygen than an elite athlete, says Dillon.

Flight chambers

Dillon, and colleague Dr Robert Dudley from the Smithsonian Tropical Research Institute in Panama, wanted to find out more about how bees flew at different altitudes.

They caught bees flying at 3200 metres and put them in air-tight plexiglass flight chambers, which were able to have their air pressure reduced to simulate different altitudes.

"We found that on average all the bees we tested could fly above 8000 metres and we had bees that flew above 9000 metres," says Dillon.

The researchers found that the bees were able to create lift by moving their wings through a bigger angle.

"They're not increasing how quickly they beat their wings, they are just beating their wings through a much bigger arc," says Dillon. "So they can push more air down per amount of time and that allows them to fly at these really high altitudes."

But Dillon says he still doesn't know how the bees are able to fly with so little oxygen at high altitudes.

"It's remarkable that they can do it but we're not sure how yet," he says.

Extra capacity

Dillon says he does not think that the bumblebees actually fly at the extremely high altitudes tested.

"I would wager that they fly as high as there are flowers," he says.

Instead, says Dillon, the bees extra flight capacity is likely to be used for other purposes such as carrying heavy loads at high altitudes.

"Sometimes they can double their body mass when they are filling up with nectar," he says.

The extra capacity could also be useful for accelerating quickly to escape predators.

The researchers now want to see whether bumblebees that live at specific elevations have developed different flight performances, and they would also like to work out how they can deliver oxygen under the demanding circumstances provided at high altitudes.

Tags: animal-behaviour, physics, invertebrates-insects-and-arachnids