Bumblebees can't fly - a further comment

David J. Tyler (D.Tyler@mmu.ac.uk)
Fri, 10 Jan 1997 14:37:53 GMT

Nearly a year ago, on Tue, 13 Feb 1996, Art Chadwick sent us the
following:

"The following was posted to an entomological discussion list by
Paul C. Johnson at UNH. I include it (without the authors
permission), because it is an oft heard story which is, of
course, nonsense in its usual context.

'Bumblebees CAN fly! The oft heard ridicule of scientists that
say a bumble cannot fly because its wings are too small, in spite
of the evidence of their own eyes, is based on a
misrepresentation of an incident that occurred in the 1930s.
McMasters (in the Amer. Sci. 77:164-169) reports that a noted
Swiss professor of aerodynamics at a dinner party with biologists
was asked about the aerodynamics of wasp and bee wings. He
performed some calculation for the bumblebee based on a smooth
wing and got a low Reynolds number "proving" the bee incapable
of flight. He obviously knew that the calculations were
simplistic, and later (after examining a wing under a microscope
and noting the bent and folded nature of the wing), corrected his
error, but like the news media of today, the correction received
little notice.'"

The further comment from me is that I don't think Johnson's
report does justice to the problem. It would appear that
scientific analysis of insect flight generally has struggled to
provide satisfactory results.

Alexander (1996) says: "In previous attempts to explain insect
flight by conventional aerodynamics, bold liberties were taken
with the physics". Basically, as I understand it, the wing was
divided into thin slices, the movements of air over each slice
were studied separately, and the resultant lift forces
aggregated.

Alexander (1996) again: "In some cases (for example, locusts),
he "quasi-steady" approach appeared to explain flight adequately.
But in others ..., the predicted lift forces were much too small
to keep the insect airborne, and various "unsteady" effects were
suggested ... Meanwhile, more and more cases were found in which
conventional steady aerodynamics failed".

A significant step forward has been made by Charles Ellington's
research group at Cambridge University, UK. Although leading-
edge vortices have been invoked before to explain how lift forces
could be augmented, they have had limited empirical investigation
and validation. Ellington et al (1996) have convincingly
demonstrated the existence of these vortices, and have also
discovered an axial (spanwise) flow component which they find to
be essential for the stability of the vortices. This effectively
solves the problem of insect flight - and this includes the
bumble bee problem! Research still needs to be done on how the
vortices are generated and how the stable spanwise flow component
is maintained.

I have two observations and comments.

1. Scientists do not serve the cause of science by giving the
impression that technical problems are solved when the reality
is that there are still major problems! The Paul C. Johnson post
cited earlier seems to me to be falling into this trap. I would
like to see a lot more honesty about the current status of
research - where we make it clear where our ideas are tentative
and in need of validation/modification as well as where our
analyses and theories are successful.

2. The more we research living things, the more we find
structures and systems which far surpass those which humans have
made. Adrian Thomas, one of the research team, is reported as
saying: "If you could get a commercial application, you would
have a jumbo jet with wings one-tenth of the present size. And
with smaller wings, you have less drag and need to use less fuel.
The most likely commercial use would be for turbines. It could
mean we have electricity-generating wind turbines not much bigger
than satellite dishes" (Derbyshire, 1996).
Humans need an intelligent design input to enhance the
performance of our technological creations; if natural selection
acting on mutations has the capability of producing such
exquisite performance "machines", we need a much more convincing
empirical justification than is presently available.

References:

Alexander, R.M. 1996. Smokescreen lifted on insect flight.
Nature, 384, (19/26 December), 609-610.

Derbyshire, D. 1996. How flight of bumble bee defies reason.
Daily Mail, (December 19), 22.

Ellington, C.P., Berg, C.v.d., Willmott, A.P. and Thomas, A.L.R.
1996. Leading-edge vortices in insect flight. Nature, 384,
(19/26 December), 626-630.

Best wishes,

*** From David J. Tyler, CDT Department, Hollings Faculty,
Manchester Metropolitan University, UK.
Telephone: 0161-247-2636 ***