Bumblebees can't fly?

Bumblebees are quite impressive insects: They make a nice humming sound, they cause a small stir when flying over patches of dusty ground, and with a mass of nearly a gram, they are heavy enough to bend clover flowers under their weight when landing to feed nectar.



And, of course, bumblebees cannot fly according to the laws of aerodynamics, or so goes the myth. This story, often invoked by people wanting to dismiss results of scientific reasoning, seems to go back to the 1930s, to students of Ludwig Prandtl, a pioneer of aerodynamics at the University of Göttingen in Germany.

As so often, there is some truth also to this myth: If one starts from the assumption that the uplift force comes about as for an airplane wing, this is fine to understand the flight of large birds. But this assumption works much worse for small birds and bats, and it fails for insects such as bumblebees. Obviously, bumblebees have found clever way to fly very different from that of airplanes.

But they don't defy the laws of aerodynamics anymore: The issue of Physical Review Letters of September 4, 2000, besides discussing Prospects of Detecting Baryon and Quark Superfluidity from Cooling Neutron Stars and Magnetic-Octupole Order in Neptunium Dioxide, had a paper by Z. Jane Wang with the unassuming title "Two Dimensional Mechanism for Insect Hovering". But as the abstract explains Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. [...]". (Phys. Rev. Lett. 85 (2000) 2216-2219).

Snapshots of the vorticity field of the moving wings (black). The illustration, taken from Phys. Rev. Lett. 85 (2000) 2216-2219, shows the formation and dynamics of a "dipole jet" of vortices, which creates the uplift force that allows the insect to hover.

It seems that the rapid motion of insects wings creates tiny vortices in the air that keep them aloft. This is especially important when hovering around a clover bloom. Luckily, bumblebees can fly without reading the PRL.

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• The myth of the bumblebee an its origin is discussed in "The Strange Case Of The Bumble Bee Which Flew" by K.P. Zetie. You can find more background and references in Ivars Peterson's MathTrek of September 13, 2004, "Flight of the Bumblebee".


• For more on the flight of insects, check out the web site of the Animal Flight Group of the Department of Zoology, University of Cambridge, and the web site of the research group of Z. Jane Wang at Cornell University. At the List of publications, you can download, among lots of other papers, the PRL from 2000 as a PDF file. More explanations about her work are in the Cornell Chronicle, "Insect flight obeys the principles of aerodynamics, CU physicist proves", and the Cornell Engineering Magazine, "The Truth about Bumblebees and other insects". On the work of the Cambridge group, and of a Berkeley group who pointed out the role of vortices and viscosity in insect flight, see "The buzz on bumblebees" in the November 2001 issue of plus magazine.

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Physics, Bumblebee Myth