Wednesday 25 June 2014

Swallowtail Butterflies.

"Papilio Machaon Britannicus" is the posh name for a magnificent species of Butterfly, more commonly known as "Swallowtails".
From late May to early July these large, beautiful insects take to the air and fly strongly over the Norfolk reed beds.

We took our cameras to How Hill near Ludham in search of these fascinating creatures.  Through two of the hottest days of the year we waited, in company with other enthusiasts, hoping to catch a glimpse of the elusive "Swallowtail".

"Swallowtail Butterfly" (Photo courtesy Tony Hisgett)

The British "Swallowtail" is a rare sub species that is only found in and around the Norfolk broads.
For five short weeks in summer the "Swallowtails" emerge, mate and lay their eggs on stems of Milk-parsley (Marsh Hog's Fennel).

Milk-parsley, a distant relative of the humble Parsnip, is the key to the "Swallowtails" life cycle and ultimate survival.  The plant grows in the Norfolk wetlands and is the essential food plant of the "Swallowtails".

The fragility of the species was dramatically illustrated at Wicken Fen in Cambridgeshire during the 1950's.  There the wetland habitat was reduced from over 100 hectares to less than ten due to agricultural activity over many years. As the water table dropped scrub land overwhelmed large tracts of the marshes around Wicken Fen.   Slowly the Milk-parsley disappeared and the Cambridgeshire "Swallowtails" became extinct.  Parts of the fens were flooded in an attempt to re-introduce the species  with Norfolk stock.  The project failed as did subsequent attempts leaving the Norfolk Broads as the last outpost for one of Britain's most spectacular butterflies.

For the moment the  Norfolk "Swallowtails" seem to be holding their own and are reasonably safe as long as the Milk-parsley survives.  By mid July most of the eggs have been laid and a few weeks later the caterpillars are soon feeding on their precious food plant.  The young caterpillars are very unspectacular in their appearance, resembling bird droppings to fool would be predators. The caterpillar or larva will moult three times before it pupates.  The adult caterpillar assumes a very colourful striped appearance after it's final moult.  

Caterpillar After 3rd Moult (Courtesy Wikimedia)
The caterpillar's defence against predators is the osmeterium, a horn like organ situated just behind the head.  This is deployed if the larva is threatened, giving off a pungent smell, similar to rotting pineapples.

The Osmerterium (Courtesy  Wikimedia)

In spite of this bizarre deterrent large numbers of larva are taken by birds and spiders long before the they transform into pupa.  Caterpillars that do survive make their way down the stems of reeds or similar plants, camouflaging themselves with green or dark brown colouration to suit their surroundings.  Here they overwinter waiting for the warm summer sun when they will emerge as exotic butterflies.    

"Swallowtail" Pupa (Courtesy Wikimedia)

At How Hill, after many hours of waiting, we were rewarded with several "Swallowtails" fluttering across the meadow and alighting on the thistles to refuel with nectar.  They remained just long enough for us to capture precious seconds of their extravagant display before they made off across the marsh and out of sight.  

The "Swallowtail" is protected by the Wildlife and Countryside act.

"Across my dreams, with nets of wonder
I chase the bright elusive butterfly of love."
                                     Dolly Parton

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