Britain鈥檚 most magnificent butterfly, the swallowtail, was a 鈥渕ust-have鈥� species for every serious Victorian collector. Its rarity made it all the more desirable: Britain鈥檚 unique subspecies Papilio machaon britannicus lived only in the remote and inhospitable fenlands of East Anglia. The prospect of catching your own carried just a whiff of danger.
At the height of the craze, thousands of amateur entomologists endured long journeys by stagecoach or on horseback for the sheer thrill of chasing swallowtails through sedge and reed. There was no stopping the slaughter: virtually every collector killed as many butterflies as possible.
Now the swallowtails鈥� desiccated husks are preserved in natural history collections all over the country. Yet they鈥檙e more than mementos of a misguided mania. Close scrutiny of the specimens has turned up vital clues to the long-term health and viability of today鈥檚 butterfly populations. As unlikely as it may seem, the legacy of the Victorian killing spree could be wildlife conservation strategies that actually work.
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IN 1871, the French brothers went 鈥渕achaon-hunting鈥� in the Cambridgeshire fens. They drove their pony and trap 鈥渁long one of those everlastingly flat Cambridge roads鈥� until at long last they arrived at a public house, aptly named 鈥淔ive Miles from Anywhere鈥�. With the aid of a jumping-pole kept at the pub for entomologists to use, the men vaulted the water-filled drainage ditch and had soon found their quarry in the fen beyond.
鈥淢y brother was over first,鈥� D. J. French recounted, 鈥渁nd before I could follow a hearty shout informed me that a Swallowtail was captured.鈥� Three minutes later, he too had netted a swallowtail: 鈥淥h, 鈥檛was a pleasant sight to see! The next two hours were exciting ones indeed, for no sooner had I pinned an insect than another was seen.鈥�
Butterfly after butterfly was caught up in the gauzy folds of collectors鈥� nets, each prize immediately speared with a pin, ready for the display cabinet in some Victorian parlour. Natural history had become a respectable middle-class pursuit. It could even provide an entr茅e into the scientific establishment of the day. Many an esteemed entomologist of the 19th and even 20th century began life as an avid butterfly collector.
As Britain鈥檚 only example of the family Papilionidae, whose members are among the largest and most beautiful butterflies in the world, the swallowtail excited Victorian collectors like no other species. A favourite hunting ground was Wicken Fen, a short hike north of Cambridge, and just down the road from the Five Miles from Anywhere pub. The fen was famous for its plentiful swallowtails, and entomologists came from all over the country to capture as many as they could. Gradually, however, the swallowtail became harder and harder to find.
Worried entomologists began to discourage the wholesale destruction of swallowtails. And in 1889, part of Wicken Fen became Britain鈥檚 very first nature reserve. But it was all too late, and by 1952 the swallowtails had vanished. Today, the species hangs on in East Anglia, but only in the Broads, a patch of wetlands along the Norfolk coast.
So what went wrong for the swallowtails of Wicken Fen? In search of clues, Jack Dempster, an insect ecologist working at the Institute of Terrestrial Ecology at Monks Wood in Huntingdon in the 1970s, had the bright idea of examining specimens stashed away in collections. He tracked down eight museums that had specimens from either Wicken Fen or Norfolk. Perhaps, he thought, there might be some physical differences between the two populations that would help to explain why the butterflies of Wicken Fen went extinct.
Dempster suspected that isolation was the key to the Wicken disaster. Once, Wicken Fen had been surrounded by an impressive area of fenland. But starting in the Middle Ages and continuing until the 1850s, more and more of this fenland was drained for agriculture. By the early 1800s, Wicken still had swallowtail-friendly fenland nearby-at meres such as Whittlesey, for instance. Dempster even found two specimens labelled Whittlesey 1819 and 1821 in collections at the University of Oxford鈥檚 Hope Museum. But Whittlesey mere, the last to go, was drained in 1852, leaving Wicken Fen completely isolated. The closest surviving populations of swallowtails were 160 kilometres away on the Norfolk Broads. The swallowtails at Wicken were marooned, with no prospect of reinforcements from outside.
The butterflies may have been dead for a century or more, but signs of their increasingly lonely lives are still there to see-built into their bodies. After measuring hundreds of museum specimens, all labelled with their date of collection, Dempster found a marked difference between the butterflies of Wicken Fen and those from Norfolk. The isolated Wicken specimens had smaller wings and skinnier thoraxes. Dempster thought the slimmed-down thoraxes-clearly less well endowed with beefy flight muscles-might be evidence of an evolutionary trend towards reduced mobility.
After the wholesale drainage of their neighbourhood, the Wicken Fen butterflies had nowhere to go. So why invest valuable resources in building flying muscles, when any butterfly that fluttered off beyond the reserve in search of partners or territories was doomed to die, stranded in an inhospitable landscape? Butterflies with strong wings and a penchant for using them were steadily bred out of the population.
The timing of the change in the Wicken butterflies fits the theory: thorax size decreased markedly after 1850. Intriguingly, by around 1920 the Norfolk butterflies had also begun to show a decline in wing musculature, which Dempster suspects was linked to habitat loss in the Broads after the First World War.
To test his idea further, Dempster set up a flying competition for living swallowtails from the Broads. He found a clear link between thorax size and aeronautic prowess: those with slender thoraxes proved to be weak flyers.
The message from Dempster鈥檚 study of the long-dead swallowtails is telling: as wild populations become isolated on tiny islands of hospitable land, they become less than they were. Entomologists have estimated that most British butterflies-perhaps as many as 85 per cent-now live in closed populations. They tend to stay put. But Dempster suspects that this wasn鈥檛 always the case. If the physical changes he found in the swallowtails reflect a change in mobility forced upon the species through isolation, the current lack of movement in other butterflies may signify a species in trouble.
Already, conservationists are taking note. There is growing recognition that no species can persist for long in pocket-handkerchief nature reserves. It is vital to create conditions that enable a species to look after itself, says Dempster. To do this, we have to look beyond reserves to ensure that semi-natural habitats persist to act as stepping stones for migration. In the long term, perhaps no population can persist in any one place, weathering the vagaries of climate, food supply and predation, without the prospect of recolonisation from outside. Perhaps all those Victorian swallowtails did not die in vain.