Monday, 26 June 2006

Trust works to secure Swallowtail's future

The reserve at Wheatfen Broad is well worth a visit at this time of the year. Situated between Surlingham and the River Yare, the area is used as a spillway during the winter to reduce the risk of flooding in Norwich. In late June it is alive with the bird and insect life attracted to the mixture of carr woodland, fen and reedbed. The cottage at Wheatfen Broad was home to Ted Ellis (the great naturalist and broadcaster) for forty years and the reserve itself is now managed by the Ted Ellis Trust, in memory of his achievements.

The reserve is also home to the swallowtail butterfly, one of our rarest and most spectacular species. The native race, britannicus, with its striking cream, black and blue markings, occurs only around the Norfolk Broads, where it can be observed on the wing from late May through to mid-July. The adults tend to fly on hot, cloud-free days, searching for potential mates and (in the case of the females) suitable sites for egg-laying. Like many of our butterfly species, the swallowtail caterpillar is associated with one particular food plant. In this case it is milk-parsley, a native species favouring tall-herb fens and which, like the swallowtail, now has a much-reduced distribution centred on the Broads. Swallowtail eggs tend to be laid on prominent plants, either those that stand clear above the surrounding vegetation or those positioned on the edge of paths cut through the fen. The eggs, which darken as they mature, are surprisingly easy to find – it’s just a case of checking the most likely plants. The tiny caterpillars initially resemble bird droppings but, after the second of several moults, they adopt a conspicuous green, black and orange colouration – a warning to potential predators of their unpalatable nature.

Swallowtails can be seen at a number of our broadland nature reserves, including Strumpshaw, Hickling, Catfield Fen and Wheatfen and genetic studies have shown that there is good interchange between the various populations. A detailed understanding of the habitat requirements of the swallowtail has allowed the development of habitat management regimes sensitive to the needs of both the butterfly and its food plant. Management of sedge fens on a three-year rotation allows milk-parsley to flourish, bolstering swallowtail populations and helping to secure the long-term future of this species. However, there are other risks that need to be taken into account, including any lowering of the water table, pollution of ground water by nitrates or phosphates and scrub invasion. Thanks to the efforts of the Ted Ellis Trust, Wheatfen seems secure from these threats for now. Let us hope that this wonderful butterfly continues to thrive.

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