How do insects compensate for reduced air density at altitude?

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Steven Broyles

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Steven Broyles  asked the Naked Scientists:

Hello Chris,

Dave reported on a recent show that there are bumblebees high in the Himalayas. Given that air pressure is lower and air is less dense at high elevations, do bees and other insects at high elevations have flight adaptations to generate the same lift?

Lift is proportional to the density of air that is being displaced by wings.  Are their wings proportionally longer?  Do the insects fly faster than insects at lower elevations?
Thank you,
Cortland, NY, USA

What do you think?


Offline RD

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How hard is it to swim in syrup?

Common sense would tell you that swimming in syrup would be harder (i.e., slower) than swimming in water. Common sense would also argue against actually trying to concoct a field test. Notwithstanding conventional wisdom, someone did and the results are surprising.

What might sound like a trivial question is actually a fundamental question of physics. Back in the 17th century, Isaac Newton and his contemporary Christiaan Huygens argued whether an object’s speed through a fluid would depend on its viscosity. Since neither had access to competitive swimmers or a pool full of syrup this particular argument remained theoretical until the present day when an experiment was conducted at the University of Minnesota with a 25-meter pool filled with the sticky guar gum. 16 volunteers then swam in both the syrupy goo and water and the times were almost identical.

The reason for the similarity of times is that while you experience more “viscous drag” (basically friction from your movement through the fluid) as the water gets thicker, you generate more forwards force from every stroke.
The two effects cancel each other out.

The study was published in the American Institute of Chemical Engineers Journal and summarized in

Analogously differences in air density would not necessarily alter the speed of a flying insect.
« Last Edit: 01/11/2008 19:03:21 by RD »


Offline thedoc

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Hear the answer to this question on our show
« Reply #2 on: 19/04/2016 17:21:20 »
We discussed this question on our  show
Kat Arney put this question to Cambridge ecologist, Felicity Bedford...
Felicity - It’s more to do with the way that their wings move than a specific physiological adaptation for them to be able to fly, as such. So the ways that bees fly generally is a little bit different to how you might expect. Their wings don’t actually go up and down - they go backwards and forwards and the lift is generated because the wings are at a slight angle and they create little vortices at the ends of their wings. Low pressured air lifts the bees. So that’s how they fly and that’s one of the things which cause a little bit of confusion when people were looking at bees early on and trying to say how on earth do these things get off the ground.
Kat - There’s that whole thing about - Oww bumblebees shouldn’t be able to fly, ha ha - but clearly they can.
Felicity - Yes. A myth started by an entomologist of all people. But they can fly, they’re very good at it and it’s because of this almost helicopter-like movement that they do that. So when they’re at high altitudes - there’s a paper by a group that took some bees into the lab, put those bees into different air pressures inside containers and they looked at the way their wings were moving. And bees in the lower pressures were actually beating at the same rate, so same number of beats. Those beats were taking a larger arc, they were scooping more air effectively with that wing beat, so they were going further with their wings to generate more lift.
Kat - Does this mean that they’re having to use more energy? Do bees in the Himalayas get tireder? Do they need to eat more nectar?
Felicity - I guess they would do. They’re certainly doing more movement for each wing beat. Their wings are moving faster within each wing beat to cover that slightly further distance and effectively use more of the minimal air that is there.
Chris - Why is the frequency the same? Why didn’t they just beat their wings faster - is that a nervous system pre-programmed thing that the wings have to beat at a certain rate, therefore they can’t change that?
Felicity - I don’t know. I guess it something to do with bees do vary the way that they fly generally. They’re over-engineered so that they can carry pollen when they’re foraging and they can carry a lot more than their own body weight, in fact despite them being this large insects with small wings and, of course, they need to be able to adapt their flight to escape predators as well. So there is that adaptation within bumble bees generally even without taking this altitude into account and this must be one of the ways in which they can compensate.

Click to visit the show page for the podcast in which this question is answered. Alternatively, [chapter podcast=1001336 track=16.04.19/Naked_Scientists_Show_16.04.19_1005027.mp3] listen to the answer now[/chapter] or [download as MP3]
« Last Edit: 01/01/1970 01:00:00 by _system »