Thursday, 6 January 2011

A Feather Beetle

Searching a sample of leaf litter which had accumulated in a ditch beneath oak trees, I found this odd little beast.
Its name takes up more room than the animal. It is less than one millimetre in length and you can only make out its structure with a microscope.
You cannot make out the details of the body because it is too opaque for the microscope. You may make out enough of the shape to see that it is an insect.
The remarkable structure is the great feathery excrescence at the end of the body. The books say that this represents  its wings. There are a large number of ‘cilia’ projecting from each side of the two central axes. These 'cilia' appear to be hollow. Each cilium has fine projections along the length.
What can be their function? I discover in a Russian journal [Zoologičeskij žurnal 2008, vol 87 pp 181-188] that A.A. Polilov has examined the structure of these beetles, but little more is known. He found that many internal organs are severely reduced (even allowing for the minute size). He says..(I quote) ..”The most important among them are the following: the absence of midgut muscles, reduction of two malpighian tubules (i.e. the nitrogenous excretory organs), the decrease in the number of abdominal stigmas (i.e. breathing pores), the strong reduction of the tracheal system (respiratory system), the absence of the heart, reduction of the circulatory system …”. He also lists reduction of the nervous system.
This information may help us to surmise what the function is. The ‘cilia’ appear to be hollow and empty.  It would seem unlikely that the cilia replace the excretory system. We know that the respiratory system of breathing pores and the air tubes (the tracheae) are reduced. Is it not likely that these ‘feathers’ are in fact the breathing system of this minute insect, and that gaseous exchange occurs across their relatively immense surface?
Then we might conjecture on the evolution of these creatures. Could it be that these ‘feathers’ are most effective under water? Is it that the beetles only live in waterlogged conditions or were their ancestors water living beetles?
It is said to be found in most regions of Europe and beyond into Asia.

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