Catching a glimpse of the UK's biggest butterfly

Catching a glimpse of the UK's biggest butterfly


Posted 16th Jun 2017


Sunny days on the Norfolk Broads will bring the wonderful sight of swallowtails flitting over reed, sedge and fen, while the edges of secluded paths will be brightened by hemp agrimony, loosestrife, ragged robin and marsh orchid

The largest of UK butterflies - and also one of the most localised - is a beautiful sight and one that is well worth the wait.

Their small dark chrysalises will winter in the reedbeds, and when the temperature is right, adults will emerge, drying their wings on the local vegetation before taking flight. The adult butterfly will feed on all species of flower but prefer yellow and purple ones that can be found on red campion and yellow iris.

When mated, females will lay their eggs singly on the leaves of the milk parsley - a few weeks later, the small, blackish caterpillars will emerge to feed on the host plant. Once fully formed, the large caterpillars are impressive green beasts, with bulging horns that will frighten off predators. If the caterpillar feels threatened, two horn-like bright orange scent glands will emerge from the back of its head, and will produce a smell - incidentally this has been likened to pineapple.

The swallow-like tail of the butterfly will play an important part in it's survival as they mimic antennae. These, plus two red and blue 'false eyes', confuse predators into thinking they are facing a two-header butterfly.

How to see one

Do some research before visiting, so you can find out how to identify milk parsley - this is their food plant. Check any plants you come across for signs of the green and black stripy caterpillars, which could be hidden amongst the leaves. Remember to pick a still, warm day, and take your binoculars - they are very fast butterflies and most likely will not sit still.

The British race is now limited to the Norfolk broads, although in 2014, migrant swallowtails from the continent were spotted hatching in Sussex. Despite being a rare British insect, if you visit one of the sites on a windless day between late May and mid-July, you could be lucky enough to spot one.

Hickling Broad should be your first port of call, with marsh harriers, bearded tits and the common crane all adding to your day's highlights. Ranworth Broad could also be worth a visit, as you cuold potentially spot a swallowtail before leaving the car park.

Other sites are:

Norfolk, Upton Broad and Marshes

Norfolk, Alderfen Broad

Norfolk, Barton Broad

Norfolk, Cockshoot Broad

Information courtesy of The Wildlife Trusts

Image courtesy of © Brian Francis





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