Saturday, July 28, 2007

The Peacock Butterfly Inachis io

I am an amateur naturalist on a mission to identify and blog all the life in my garden.
It has been the wettest UK summer on record with the river Thames breaching its banks and flooding parts of Oxfordshire.

Despite the incessant rain I am pleased to still be seeing plenty of insect life in my garden. The Peacock butterfly (Inachis Io) in photo 1 (click to enlarge) was amongst a flutter ( the collective noun for butterflies I believe) of half-a-dozen feeding on the flowers at the front of my garden (at (1.5,0.5) - see here).

Peacock butterflies can live a surprisingly long time (11months according to this site) and hibernate over winter from September/October. The outer surface of the wings is dark brown, providing camouflage for the butterfly when it's hibernating in dark places such as holes in trees and garden sheds.

The striking feature of the Peacock butterfly are of course the eyespots on the wings. Scientific studies have shown that these have a powerful deterrent 'fear' effect against predatory birds such as blue tits.

Something I found remarkable is that along with their eyespot defense, Peacocks can emit a hissing sound when attacked. They achieve this by rubbing together structures in their forewings. According to the paper above, these sounds apparently have little effect on birds, but other studies have shown that clicks emitted in the ultrasonic have a deterrent effect on predatory bats.

I read here that happily Peacock butterflies have enjoyed a healthy expansion of their populaton in recent decades. Numbers in Finland have more than doubled in the past twenty-five years. The distribution map on this site shows that Peacocks are essentially ubiquitous in Britain, save for the far North of Scotland.

Finally, regular readers of this site will know that I am fond of generating images using my hobbyists microscope. To get microscopic images of my Peacock would have meant killing it - something I wasn't prepared to do. As it happens however, when I originally bought my microscope I also bought some pre-prepared slides of butterfly 'parts'. I don't know to what species they belong (is anyone out there expert enough to know from the image alone?), but for no other reason than its beauty and fascination-value, photo 2 (click to enlarge) shows a 100x image of a butterfly proboscis - the 'drinking straw' mouthpiece through which a butterfly sucks up nectar. As a non-butterfly expert, I was a little puzzled by the presence of two tubes in my microscope slide. My understanding is that a probscis is indeed formed from two tubes however, but that normally these are 'zipped together' shortly after an adult butterfly emerges from its cocoon. I wonder whether this implies that my microscope slide was prepared from a young butterfly - or maybe there's another explanation? And as a final snippet of information, in preparing this posting I came across a paper by Rusterholz and Erhardt (Ecological Etomology,22, 1997) explaining that given a choice over what to dip their proboscis into, Peacock butterflies prefer sucrose sugars over fructose, and fructose sugars over glucose - so now you know!

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