July 2014 - In Search of the Swallowtail Butterfly


Taken by Carol, shows from left to right, Judy, Jenny and Lin

On the 15th June, I spent a wonderful time, meandering around Wheatfen Nature Reserve, Surlingham, with other Bawburgh Wanderers, including Jenny Press, Carol Stephens, and Jenny's friend, Judy, investigating the varied fauna and flora, trying to find an elusive Swallowtail butterfly. These butterflies were originally named Swallowtails because of their forked tails which supposedly resemble that of Swallows. The day was overcast, and this did not bode well for us seeing the elusive star of the show, although we were assured that Swallowtails were around. We walked down paths at the side of deep reed beds and dykes, amazed at the number of orchids growing, both Marsh and Spotted varieties. The rare plant, Marsh Pea, seemed quite common here growing among the reeds, as was Ragged Robin. We could hear the constant song of Reed Warblers, their song more than making up for the fact they are such nondescript looking little brown birds. We saw Small Tortoiseshell, Large Skipper and Speckled Wood butterflies. Mounds of old cut reeds evident along the dykes provided ideal areas for grass snakes to lay eggs. Many different Damselflies and Dragonflies were on the wing everywhere you looked. The ground was boggy under foot as we neared the Swallowtail view point. Yellow Irises, the main nectar food plants of these butterflies, bobbed among the reeds, but were not tempting the Swallowtails today. One of the Rangers showed us one tiny egg laid on Milk Parsley, the sole food plant of the Swallowtail caterpillar. These caterpillars possess a unique forked organ behind their head, called the osmeterium. If the caterpillar is threatened, it inverts this structure which emits a vile smelling secretion containing terpenes, with the aim of deterring the predator.  Suddenly a Swallowtail  butterfly zoomed above our heads but it was gone in a second. I knew the Swallowtail is Britain's largest resident butterfly with a wing span of about 4.5 inches, but I still wasn't quite prepared for the size.  The butterflies are on the wing from mid-May to September although numbers decline from August. They overwinter as chrysalises on sedge or reed stems, above flood levels. Due to the reed bed management at Wheatfen, the Swallowtail butterflies are gradually increasing in numbers in this area. Walking back to the centre for a cup of tea, we noticed many Amber Snails along the reed beds, their bodies seemingly too large for the almost translucent shell. Certainly this was a memorable day.

 

lingibson@bawburghvillage.co.uk

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