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In search of SWALLOWTAILS

PUBLISHED: 17:24 26 May 2015 | UPDATED: 12:17 02 June 2015

Swallowtail butterfly at Hickling Broad.

Swallowtail butterfly at Hickling Broad.

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The extraordinary butterfly of the Broads is celebrated by Norfolk Wildlife Trust ambassador and BBC broadcaster Ben Garrod.

Picture the scene - you’re walking through a beautiful habitat, where slow-flowing water endlessly and gently meanders past. Where an almost-continuous stretch of gently whispering reed and vibrant green sedge contrasts against a sky so blue that it looks as though a child has painted it, failing to understand that the sky can’t really be that colour. It’s warm, as the early-morning summer sun caresses your face. Finish the scene with the idea that you are looking for the largest butterfly found in that particular country and that it’s a whopper. It is bright yellow with oily black edging on its wings and electric blue flecks make it gleam as it flies by. The wings end in long trailing tails and two crimson red eye spots makes this a truly beautiful insect.

It’s a real invertebrate safari. But it’s not in the African marshes of Lake Victoria or the Bornean swamps of Asia; it’s the Norfolk Broads. Yet again, Norfolk has come up trumps for memorable wildlife encounters. There are places set among our local wetland habitats which are home to what is undoubtedly the UK’s most iconic species of butterfly; the aptly named swallowtail. Swallowtails (so named because of the resemblance of their wingtips to swallows’ forked tail feathers) are generally found far and wide, from Africa and Asia, to Europe. But our British swallowtail is a unique subspecies, found only in Norfolk and nowhere else in the UK. A subspecies is created when a population of a species becomes physically, genetically or behaviourally different from its original species but is not different enough to be elevated to being a whole new species. It’s not a hard and fast system set in stone but for these particular butterflies, they differ in their preference for fenland habitats and have a significant amount of black in their wings, setting them apart from their European counterparts.

These big, strong-flying lepidopterans are surprisingly fragile and fussy, only feeding on one particular plant, milk parsley, which is in turn only found in particular habitats. Their large bulbous green caterpillars are striped with black and orange streaks, allowing the larvae to amble around with that self-assured impunity that only comes when you know that you’re too toxic to be eaten. But for those particularly pesky predators unwilling to take the hint, the swallowtail larva has a stinky surprise hidden away; the osmeterium. This bright orange branched organ sits behind the head and when threatened, it pops out and releases a noxious odour, similar to that of a rotting pineapple ... convincing even the most determined would-be diner that this is most definitely not a tasty treat.

When these gaudy larvae turn into the beautiful adults, the Broads comes alive. From May to mid-July and, in good years, with a second clutch emerging from mid-August to September, swallowtails can be seen at Norfolk Wildlife Trust sites such as Ranworth and Hickling Broads. You feel as if you’re stalking an almost mythical animal . . . something strong yet delicate, real yet ephemeral. As you scan every movement and realise that holding your breath won’t actually increase your chances of seeing one, you may just be rewarded with a close encounter with one of our rarest and most beautiful wild animals. ◆

For details about visiting NWT Ranworth Broad and NWT Hickling Broad, which both have visitor centres and offer guided boat trips, plus lots more about Norfolk’s wildlife in June, visit www.norfolkwildlifetrust.org.uk

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