Saturday, June 4, 2011

Aerostatic skeletons

Teleopsis sykesii - Diopsidae, a common stalk-eyed fly in the Western Ghats
The strawberries at the ends of the handle-bar are the eyes.
It was not too long ago that I first learnt about an insect with eyes on stalks. Somehow nobody in our entomology faculty had introduced it in our student days and the idea had been drilled in that stalked eyes were found only in the crustacea. When I first came across it and discovered that it was hardly uncommon, it was a bit depressing to see that there were no experts who could identify it to species. Apparently problems had been created in the museums with labelling errors. I had uploaded my photographs on Wikimedia Commons and only recently obtained a species level identification of it - actually a confirmation of my own part-guess based on old literature - Teleopsis sykesii (named after Colonel Sykes). A redescription of the species that makes use of photographs of yours truly as well as the superior images of Karthik has just been published.

  • H. R. Feijen, C. Feijen (2011) On the biogeographic range of the genus Teleopsis Rondani (Diptera: Diopsidae), with redescription of Teleopsis sykesii from India and description of a new species from Borneo. Zoologische Mededelingen, 85:141-159. (PDF)
It is interesting that this these are not the only flies with elongated eye bases - apart from the Diopsidae, the feature is also seen in the Richardidae. A very interesting piece of footage in one of Sir David Attenborough's Challenges of Life - shows how the fly emerges from the pupa looking more or less like a typical fly and then inflates the tubular stalks with air to form the elongated eye stalks. In most other insects, this kind of expansion of structures is done by pumping liquids that then subsequently dry - as in the case of the Lepidoptera. The use of pneumatic (perhaps aerostatic is the equalent of hydrostatic) structural elements seems to be rather rare in life - indeed I have not been able to find any other. Strangely enough however, there are a number of ideas in robotics (including the art of Theo Jansen) and tent making that use pneumatically operated structures, after all it means you use the air around you and save yourself from carrying extra construction baggage.


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