Why a fly can fly like a fly
by Carl Wieland
The humble fly hovering over a garbage can is routinely capable of some high-speed
aeronautic manoeuvres that have long boggled the minds of aircraft designers and
engineers. If a male fly chasing a potential mate sees her change course ever so
slightly, he will respond with an appropriate change of his own in just 30 milliseconds!
It has long been known that the amazing stability of flies as they zip around has
a lot to do with the two tiny club-shaped ‘balancing organs’ they have,
called halteres (see Figure 1, right). Some insects have four wings, while others,
like the so-called ‘true flies’, have two (hence their ordinal name
Diptera). Evolutionists believe today’s flies descended from four-winged ancestors,
of which the rear two wings have become ‘vestigial’ or reduced in their
flight function to become the halteres.
Figure 1. A fly showing one of the club-shaped ‘balancing
organs’ or halteres. Arrows show the pathway.
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There is of course no scientific reason to deny that the halteres are incredibly
well designed, efficient organs in their own right. They have long been known for
their function as flight stabilizers, like gyroscopes on airplanes that prevent
excessive roll, pitch or yaw. Part of the way this works is that the halteres mostly
beat in antiphase to the actual wings. But since such a stabilizing function would
tend to make the fly keep flying straight, how does it manage to ‘disable’
this gyroscopic function in order to change course so quickly?
Researcher Dr Michael Dickinson of the University of California at Berkeley, along
with a number of colleagues, long knew that flies will perform intricate flight
manoeuvres in response to visual stimuli (a fly swatter coming down on them, for
instance!). Sophisticated experiments in which flies were tethered in little corsets
had shown that images perceived by the fly’s eye-brain system would cause
automatic changes in wing activity. Yet a mystery remained, in that for years no
one had been able to find evidence of any connecting nerve fibres between the brain
and the muscles that controlled the wings.
The breakthrough began when Dickinson was reviewing a much earlier paper that described
in great detail some very intricate musculature controlling the halteres. His team
then performed more experiments which showed that visual cues while flying did not
affect the wing muscles, but significantly affected the muscles controlling the
halteres. This suggests that visual information flows directly from the eye/brain
to the halteres, not the wings.
Figure 2. A fly showing one of the club-shaped "balancing
organs" or halteres. Arrows show the pathway.
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The team then demonstrated that stimulating the halteres affects the wing-beat.
From all this, Dickinson proposes a much more sophisticated function for the halteres
than previously realized. The traditional view has been that as a fly begins to
tumble, say, the beating halteres are deflected (by the Coriolis effect), which
stimulates some nerve cells long known to be at their base. This then sends the
appropriate signals to the muscles controlling the main flight wings.
The picture would now appear to be a great deal more complex (see figure 2, left).
Not only do the halteres send their controlling signals when affected by direct
manoeuvres, but a visual stimulus (e.g. an approaching fly-swatter in mid-air) will
cause information to flow from the eye-brain system to the halteres, which act as
a relay station to the main wings.
Far from being an unnecessary detour for the electrical impulses, this makes a lot
of sense, says Dickinson. The halteres tend to keep the insect flying in the same
direction, so when it has to make a sudden turn, the halteres have to respond as
well as the flight muscles. So rather than ‘switching off one’s gyroscope’,
the halteres are appropriately fine-tuned or ‘tweaked’ for the required
manoeuvre in response to visual cues, a fraction of a second before they in turn
pass the information on to the main flight muscles. He says:
‘From an engineering point of view, this is much cleverer and more efficient.
This way you never turn off your stabilizer—you tune it so the nervous system
controls its mechanics on a moment-by-moment basis.’
Also, Dr Cole Gilbert of Cornell University has shown that the relative position
of a fly’s head in relation to its body also sends information to the wings
and halteres. All this indicates a neural network outside as well as inside the
insect’s brain, which is capable of immensely complex and sophisticated tandem
actions that eclipse our present technology. Dr Dickinson refers to many remaining
‘puzzles’ about how flies fly, and says he thinks that these creatures
are ‘more fantastic and exciting’ than anything ever dreamed up in a
science fiction movie.
Summary/conclusion
- There is no proof that flies evolved from any ‘primitive ancestor’.
- There is no evidence, either, which forces one to conclude that halteres are ‘vestigial
leftovers’ of what were once true (rear) flight wings.
- Experimental evidence indicates that halteres are part of a highly sophisticated,
and immensely complex, flight system which continues to baffle and amaze all who
study it.
- This evidence (as well as that from the fossil record) strongly supports the belief
that flies were created as flies, complete with all the necessary sophisticated
precision machinery for them to astonish us with their performances.
- Obviously, at least some of the fly types today function as part of the Curse on
a fallen Creation due to Adam’s sin.
References
- Pennisi, E., 1998. Flying by the seat of their halteres. Science,
280(5361):201–202.
- Chan, W.P., Prete, F., Dickinson, M.H., 1998. Visual input to the efferent control
system of a fly’s “gyroscope”. Science, 280(5361):289–292.
- Dayton, L., 1998. Can’t hurt a fly? Now science knows why. Sydney Morning
Herald, April 14.
- Highfield, R., 1998. A magnificent flying machine. The Daily Telegraph,
April 22, p.16.
- Anon., 1998. Fossil flies. Discover, 19(8):33.
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