On the Aerial Locomotion of Butterfly Wings

One’s perception of butterfly flight is that it is typically characterized as some undefined haphazard flitter, but quite astoundingly butterflies flutter about from flower to flower and from bush to bush in quite a precisely targeted fashion. The mechanism of aerial locomotion in butterflies is quite intriguing indeed, ranging from steady undulations to rapid, erratic bursts of activity.

Particularly, butterflies use the clap-fling ring mechanism of flight. Firstly, the wings are clapped close together and then are flung open. This creates a vacuum which consequently gives rise to ring-shaped vortices of air, which form over the wings. When the wings are flung apart, air is accelerated downwards consequently leading to lift at the beginning of the down stroke. As lift is generated, the two opposite ring-shaped vortexes of air are accelerated and shed away earthwards at the end of the down stroke, at which point they combine together and further increase lift. Essentially, the circulation of air proceeds from beneath the wings to the top of the wings, which is the direction needed to generate lift. A column of air develops downwards which balances the upward forces inflicted upon the wings.

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The clap-fling ring mechanism of insect flight, as exhibited by butterflies. (Weis-Fogh, 1973)

Butterfly wings are shifted up and down by virtue of thorax muscles. Two sets of wings are present: two forewings and two hindwings.  A network of tube-like veins, through which air runs, permeates the wings. The wings have a flexible outer part which, when employed in flight, bends to push the air backwards so as to propel the butterfly forwards. By comparison, the front part of the wings is stiff and as such, serves to generate lift. The pressure of air acts upon the hindwings in such a manner that they are raised at the downstroke but lowered at the upstroke, which collectively manifests in this distinctive wavelike locomotive pattern which butterflies so intriguingly exhibit.

Butterflies do not flap their wings rapidly, when compared to other insects  (the rate ranges from 5 – 20 times per second). Flight speeds range from 8 km/hr to as fast as 48 km/hr. Butterflies are able to travel long distances. In fact, butterflies have been observed to migrate for as much as 1000 kilometres! Butterflies can also reach tremendous altitudes. For instance, monarch butterflies have been observed to fly at altitudes of 3,000 metres! Quite intriguingly also, butterflies can continue to maintain flight even when portions of their wings are damaged or removed. In fact, butterflies can continue to fly with their hindwings entirely removed, albeit with a reduced acceleration (Jantzen and Eisner, 2008).

With their intriguingly patterned iridescent features reflecting flashes of wonder and astonishment and erratic, yet purposeful flight paths firing the fascination of naturalists worldwide, it rests to say that butterflies are quite marvelous creatures indeed!

 

Bibliography

Jantzen, B. and Eisner, T. (2008). Hindwings are unnecessary for flight but execution for normal execution of normal evasive flight in Lepidoptera. PNAS 105: 16636 – 16640.

Weis-Fogh, T. (1973). Quick estimates of flight fitness in hovering animals, including novel mechanisms for lift production. J. Exp. Biol 59: 169-230.
Featured image retrieved from: wallpaperbeta.com
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