9 for 90: Swallowtail Butterfly

by Nick Acheson
Most of our Norfolk Wildlife Trust 9 for 90, as fascinating and beautiful as they are, as characteristic of the Norfolk landscapes we have chosen them to represent, are widespread in the UK. Exceptions are the spoonbill, which breeds only in North Norfolk and whose whole UK population spends summer around the Cley to Salthouse Living Landscape; the common crane which, though now spreading apace, was for decades restricted to the Upper Thurne; and the swallowtail. No 9 for 90 species is more closely associated with its Living Landscape than the swallowtail, which we have chosen to represent the Bure Valley.
 

Swallowtail caterpillar, photo by Jo Reeve

It is hard to write about swallowtails without stumbling into hyperbole. They are the UK’s largest butterflies. Crazed and stippled in black and adorned with mirrors of sapphire and ruby, they are also quite possibly our most dramatic. Certainly they are our most tropical in appearance (belonging to a largely tropical family of butterflies). Their caterpillars keep the psychedelic side up too. Starting life as minute specks of grey and white, mimicking bird droppings, as they grow, in size and toxicity, they flush lime green, boldly hooped in black and orange. If threatened they poke a pungent, startling orange osmeterium – like an antelope’s horns – from above their faces, adding to this dramatic reedbed rainbow.
 
It is reedbed that is the critical word here: reedbed and fen. For the Norfolk swallowtail (now again spreading through the marshes of East Anglia, but very much a Norfolk native) can be found in no other habitat. Unlike continental subspecies of the butterfly, which will lay their eggs on a range of plants in the carrot family and in a range of habitats, Norfolk’s swallowtails lay only on milk parsley. This is a fussy, demanding plant of reedbed and fen, and in the UK it is also largely restricted to East Anglia. So bound is the UK – read Norfolk – swallowtail to this plant and its habitat that it is recognised as unique subspecies, an East Anglian endemic, Papilio machaon britannicus.
 
Even many decades ago the fens and marshes of the Bure Valley Living Landscape were renowned as heartland habitat for this threatened local butterfly. On the acquisition in 1930 of Alderfen Broad by Norfolk Wildlife Trust (then Norfolk Naturalists Trust), The Times of 28 July reported, ‘The swallow-tail butterfly still holds its own in the district, but a heavy toll is levied upon it every year, so that sanctuary for it as well as for the birds is most desirable.’ When in 1949 Lieut.-Col. H. J. Cator donated Ranworth and Cockshoot Broads to NWT, the Eastern Daily Press of 22 March noted that, ‘The Ranworth Marshes appear to be the headquarters of the black variety of the swallowtail butterfly […]’.

Still today the swallowtail flourishes in the Bure Valley Living Landscape, thanks to sensitive management by NWT and its conservation colleagues. Indeed since the acquisition of the first 160 acres of land at Upton Broad in 1979, NWT has actively cleared scrub in the Bure Valley, to restore some of the nation’s most important fens. This has meant far more habitat for charismatic swallowtails. It has also meant more habitat for the many other specialist species for which the swallowtail is our chosen representative.

Cockshoot, photo by Ray Jones

A walk through fen at Cockshoot, Upton or Barton Broads in summer is panic-inducing for the naturalist. Where to look, what to sniff, what to photograph, whose song is that? For a fen in summer is crazy with life. There are swallowtails, to be sure, drifting like scribbled paper scraps over flowering flags, stopping to feed on nectar from brazen stands of red campion at the woods’ edge. The margins of dykes through the marsh are busy with the bright bodies of damselflies and dragonflies. Each species has its own personality in flight. Four-spotted chasers dart in jagged lines over water, retreating to their poolside perches on last year’s broken reed stems; red-eyed damselflies lurk low in the dyke, resting like tiny twigs on lily pads; variable damselflies cling to meadowsweet and ragged robin, flitting flimsily from stem to stem at your approach; and a Norfolk hawker, emerald-eyed, zigzags above the marsh at speed, claiming this patch of flowery fen his own.

Flowers are everywhere in early summer here: the bold gold flowers of greater bird’s-foot trefoil and spikes of orchids starting to appear. Many of the orchids are dust-pink common spotted. Some taller, fleshier spikes are deeper pink. These are southern marsh orchids. Nearby marsh helleborines are growing in readiness to flower a little later in the summer. Between the many orchids the space is filled by the froth of fen bedstraw, the haze of tufted forget-me-not and the cheerful yellow of square-stalked St-John’s-wort. Leaves of meadowsweet, of purple and yellow loosestrife, of grass of Parnassus are waiting in the wetland wings for their flowers to come later still in summer.

They are the UK’s largest butterflies. Crazed and stippled in black and adorned with mirrors of sapphire and ruby, they are also quite possibly our most dramatic

For every flower there is an insect, for every insect a bird, for every bird a hungering hobby, hunting here for the summer from Africa. And for every precious patch of fen in the Bure Valley Living Landscape there is an equally important broad or carr wood, cut or grazing marsh, each with its own abundance of species, of colour and of sound. Where the reed gives way to willow a Cetti’s warbler shouts: where the willow gives way to alder a marsh tit stridently sings; where the alder gives way to oak purple hairstreak pupae nestle in the topsoil, awaiting high summer’s warmth to burst into dark violet flight.

These habitats and these species are part of a great Broadland land-and-water-scape which abounds in wildlife and is still impressively coherent along its rivers, dykes and corridors of wet woodland. The Ant flows into the Bure, which swallows the Thurne; the waters of these two NWT Living Landscapes then join the Yare and move to sea through Breydon Water. It is this flow, this connectivity, which are at the heart of NWT’s Living Landscapes. They are of course about protecting and restoring connections between nature reserves, as we have done throughout the Bure and Ant Valleys, for the free flow of wildlife and wild genes. They are about rebuilding habitats too, as we have done at Upton Broad and Marshes, putting lost pieces back in the puzzle. Crucially they are also about reconnecting people with landscape and wildlife, as we do through our events, workshops, community projects and conservation groups.

In a wild landscape all is cycle, connection and flow; all is weft and weave of genes, energy, protein and water. Summer’s female swallowtails find isolated plants of milk parsley in the fen, on which to lay their eggs. Without the water and the landscape history there is no fen; without the fen no milk parsley; without the milk parsley no swallowtail. On each plant a female will lay one egg, because the resultant caterpillars often turn to cannibalism. A caterpillar spends late summer chewing through its plant, growing fat before pupating in autumn, hiding the winter through low on a reedstem. Without the water and the landscape there is no reed; without the reed no swallowtail pupa to become next summer’s butterfly. When the adult emerges it will need to feed: on ragged robin, on yellow flag iris, on marsh thistle, marsh sow-thistle, cuckoo-flower, on all the flowers of the fen which without the water and the history of human use and care would not be here. Could not be here.

The swallowtail sits at the centre of a Living Landscape along the Ant and Bure, connected to and connecting species, habitats, people and landscape history. In the scythe-stroke of historic marshmen were its fens made and maintained. In the revolution in British drainage and agriculture, and the nets and pins of Victorian naturalists was its future threatened. In the vision of Sydney Long for a Norfolk Naturalists Trust ‘to preserve for future generations areas of marsh, heath, woods and undrained fenland […] with their natural wealth of flora and fauna’ (Eastern Daily Press, 1926) was its future secured in the Bure and Ant Valleys. The swallowtail: no other 9 for 90 species better represents the Living Landscape it has been chosen to represent. The swallowtail: East Anglian endemic, fussy eater, startling beauty, and symbol of the great wild landscapes of the Norfolk Broads.