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The aptly-named Adonis Blue has seen a rapid decline in numbers because its grassland habitat has been disappearing, but the recent hot and dry weather associated with climate change seems to be beneficial for this species.

A wing and a prayer

“Most butterflies have decreased since the 1970s and an alarming number of common species have declined severely too.” Peter Holthusen takes a look at the UK’s best-studied insects
Numbers of the UK’s most endangered butterfly, the High Brown Fritillary which was once common in woodlands across England and Wales, are finally increasing at some of its former sites.

"While 76% of species are declining, prospects for a handful of the most endangered butterflies in Britain have at least brightened over the past decade, according to the latest ‘State of the UK’s Butterflies 2015’"

More than three-quarters of Britain’s 59 butterfly species have declined over the last 40 years, with particularly dramatic declines for once common farmland species such as the discreet Essex Skipper, Small Heath, and its cousin the Wall Brown, according to the most authoritative annual survey of population trends.

 

“This is the final warning bell,” said Sir David Attenborough, President of the Butterfly Conservation, calling for urgent research to identify the causes for the disappearance of butterflies from ordinary farmland. “If butterflies are going down like this, what’s happening to our grasshoppers, our beetles, our solitary bees? If butterflies are in trouble, rest assured everything else is.”

Despite its name, the Marbled White is more closely related to the subfamily known as the “browns” than the “whites”, and is found in distinct and often large colonies. It is a particularly attractive black and white butterfly, unlikely to be mistaken for any other species.

 

But although common species continue to vanish from our countryside, the decline of some rarer species appears to have been arrested by last ditch conservation efforts, particularly in the rolling hills and ancient woodlands of the Chilterns, where several rare species of butterfly and moth, including the endangered Black Hairstreak, Adonis Blue and Striped Lychnis moth continue to thrive.

The ancient woodlands of Whitecross Green, and the nearby Oriel Wood which are managed by the Berks, Bucks and Oxon Wildlife Trust are sites where conservation management is at its best. The Black Hairstreak and Brown Hairstreak – two of Britain’s rarest butterflies – are both found here. The former species is thought to be rare due to its apparent inability to colonize new areas, even when there is suitable hedgerow or small woodland habitat nearby. Blackthorn and wild plum are the main sources of food for the Black Hairstreak and Brown Hairstreak larva.

Other butterflies recorded at the sites include the Marbled White, Wood White, Large Skipper, the beautiful White Admiral or ‘Red-Spotted Purple’, Meadow Brown, Common Blue, Orange Tip, Brimstone, Speckled Wood, Ringlet, Purple Emperor and Gatekeeper.

Whitecross Green Wood and Oriel Wood are designated as Sites of Special Scientific Interest (SSSI), and contain a large proportion of native trees and shrubs, including ash, hazel and oak. Blackthorn is abundant within the woodlands, adjoining open grasslands and at Whitecross Green, around a small pond. There are some areas of coniferous woodland that are currently being converted back to broadleaved woodland. The low-lying wood sits on a bed of Oxford clay, leading to a moist woodland habitat ideal for butterflies and moths.

While 76% of species are declining, prospects for a handful of the most endangered butterflies in Britain have at least brightened over the past decade, according to the latest ‘State of the UK’s Butterflies 2015’ report by the Butterfly Conservation and the CEH (Centre for Ecology & Hydrology) at the National Environment Research Council, with rare species responding to intensive conservation efforts.

“Overall the situation is stark,” says Richard Fox, Head of Recording at the Butterfly Conservation and lead author of the report. “Most butterflies have decreased since the 1970s and an alarming number of common species have declined severely too.” Persistent habitat destruction, through the intensification of agriculture and changes to woodland management, are believed to be the primary cause for why so many species are significantly dropping in number. Even previously abundant species, such as the Gatekeeper and the Wall Brown, have respectively seen 41% and 87% declines in abundance since 1976. Other species, including the White Admiral and Marsh Fritillary all show signs of serious decline in numbers, despite some expanding their ranges.

“On the other hand,” continues Fox, “trends over the past decade provide grounds for optimism and show that our approach to conserving threatened butterflies can stem and even reverse serious declines.” He refers to data that shows how some resident species have been growing in numbers in the past decade, with the Pearl-bordered Fritillary and the exquisite Duke of Burgundy increasing in abundance by 45% and 67% respectively, and the Dingy Skipper and Silver-studded Blue increasing in occurrence by 21% and 19% respectively.

During the last 10 years, the population of threatened species such as the Pearl-bordered Fritillary and the Duke of Burgundy which has seen a marked increase in abundance, is a clear indication that meadows and woodlands are now specifically managed to help these species. Numbers of the UK’s most endangered butterfly, the High Brown Fritillary which was once common in woodlands across England and Wales, are finally increasing at some of its 30 remaining sites in Exmoor and South Wales, showing the success of targeted conservation efforts there.

The High Brown Fritillary enjoyed its best summer for a decade last year, with numbers of the critically endangered species increasing by 180% compared with 2014 according to the UK Butterfly Monitoring Scheme (UKBMS) and Butterflies for the New Millennium, with warm spring weather also helping its caterpillars survive. Its recovery, which builds on an increase in numbers in 2014, raises hopes that this large, dynamic butterfly is no longer heading towards extinction.

As recently as 50 years ago, the High Brown Fritillary was a distinctly common sight in its former strongholds. In recent decades, lepidopterists have puzzled over its dramatic disappearance, fearing it would become the first butterfly species to fall extinct since the enigmatic Large Blue was lost in 1979.

But according to Richard Fox of Butterfly Conservation, recent “fine-tuning” of conservation management in the High Brown Fritillary’s last remaining strongholds – Morecombe Bay in Lancashire and the wilds of Exmoor and Dartmoor in the West Country – has revived its fortunes.

“There’s quite a lot of fine-tuned, targeted management on many of these sites,” said Fox. “The sites being managed specifically for the High Brown Fritillary are where this butterfly did well last year.”

The High Brown Fritillary’s caterpillars feed on wild violets found on moorland, woodland edges and rough pasture. The loss of traditional grazing in many of these areas has seen these flowers shaded out by scrub – clearing this, and controlling bracken growth, is required for both the violets and the survival of the butterfly. Then there must be precisely-timed livestock grazing in early summer to help the female butterflies locate the violet leaves on which to lay their eggs.

Even with several good years of breeding, however, the High Brown Fritillary has still declined by a staggering 62% since 1978. Fox said climate change as well as habitat loss was contributing to its decline. Like many butterflies, the High Brown Fritillary spends the colder months as a hibernating caterpillar, and these die if winters are warm and wet.

However, the ‘State of the UK’s Butterflies 2015’ report cautions that such revivals still leave these vulnerable species far scarcer than they once were. The report reveals that the causes of the decline in rare “habitat specialist” butterflies, who are only found in specific places such as chalk grassland, are well understood, and usually linked to the destruction of flower-rich grassland or neglect of traditionally coppiced woodland, such as Whitecross Green and Oriel Wood in the Chilterns.

But the reasons for the disappearance of once-common species from the wider countryside are less well understood by scientists. The Wall – an orange and brown species that gets its name from the characteristic behaviour of basking with wings two-thirds open on any bare surface, including walls and stones – has declined in abundance by 87% since 1976 and by 77% in its occurrence. So it is now seen in both much lower numbers and in many fewer locations. Climate change and pesticides may be playing a more damaging role in their declines than previously thought.

For many centuries, all butterflies and moths, like so many other insects, were often referred to simply as ‘flies’. The name ‘butterfly’ is in reality as ancient as Old English and the general conclusion today is that it originally meant ‘butter-coloured fly’ and was probably applied to the most obviously butter-coloured species in Britain, the Brimstone. To call someone ‘a butterfly’ is to suggest that they lead a flippant, light-hearted if not futile existence; ‘Butterflies’ was a popular television comedy series of the 1980s about a family with just such a lifestyle.

‘Moth’ is also Old English, which implies some early recognition of a difference between the two groups. However, moths were generally thought of as night-time butterflies and the name ‘moth’ was also used for other creatures, including cockroaches. It may originate in the same Teutonic root as ‘midge’.

I am sure that people have collected butterflies throughout recorded history. In 1895, Albert Meek the indefatigable English bird and insect collector for Lionel Walter Rothschild, found a depiction of people chasing butterflies with nets (for no very obvious reason) on a mid-14th century Flemish manuscript in the Bodleian Library. By the 17th century collecting was being carried out reasonably systematically, although curiously, the specimens were often never labelled.

By the 18th century, butterfly collecting existed as a more or less organized pursuit, the collectors calling themselves ‘aurelians’, an archaic word for lepidopterist. This name is always said to be derived from the Latin word for gold, because butterfly chrysalises are gold coloured, but quite frankly most scientists find the notion that the most significant thing about butterflies is that some have, largely imaginary, gold colouring on the chrysalis scarcely credible. Nonetheless, the name achieved immortality through a beautifully illustrated, if quaint book called ‘The Aurelian’, which was published in 1766 by Moses Harris, the celebrated English entomologist and engraver.

Because butterflies have not been considered worthy of serious note until relatively recently, the majority of them, like moths and indeed many other insect species, do not have ancient names and those in general use today, with some modification, have mostly evolved over the past 200 or so years. Many originated with the ‘Found Father’ of British butterfly study, the London entomologist, botanist and apothecary James Petiver, who, in 1717, published the first book devoted solely to British butterflies, ‘Papilionum Brittaniae Icones’.

Many of the names are passable descriptions of their appearance or colour (Marbled White); while some also include an indication of their habitat (Heath Fritillary); some recall the place where the butterfly was first found (Lulworth Skipper); some are simply expressions of wonderment, such as the Red Admiral, ‘admirable’; others even commemorate people who may have played some part in the capture and study of early specimens. Also, because there are fewer species of butterflies than of moths, it has not been necessary merely to name them after the plant on which they occur or to invent any truly fanciful names.

Nine families of butterflies are represented in Britain although some only barely. The individuals range in size from the huge 47-millimetre (2 inch) wing-span of the Monarch, or ‘milkweed’ butterfly to the barely 10-millimetre (½ inch) wing-span of the Small Blue.

In Britain as well as many other parts of the world, a butterfly was once thought to be the soul of the departed and, in some areas of rural England, such as the Outer Hebrides, the West Country and parts of East Anglia, they were believed, rather like Kittiwakes, the most seafaring of British gulls, to be dead children who had passed away unbaptized and were unable to enter Heaven.

Common butterflies are generally faring better in Scotland than in England, mirroring trends reported in other species groups, such as moths. Scientists believe that climate change may be having a more beneficial impact in the north than in the south.

Climate change is helping some species move northwards but increases in occurrence, or general distribution don’t necessarily translate into higher numbers: the Silver-washed Fritillary has flown into the Midlands and East Anglia in the last decade, with a 55% increase in occurrence, but its abundance has only increased by 6%. The Purple Emperor has declined in abundance but increased in occurrence by 135% ̶ reflecting butterfly enthusiasts’ increased skill in spotting this elusive butterfly in previously unknown locations.

Climate change is providing some excitement for the thousands of volunteers who spot butterflies for Butterfly Conservation’s recording schemes, resulting in a uniquely detailed set of scientific records stretching back to 1976.

More migratory butterflies are now reaching Britain, with the Clouded Yellow, Red Admiral and Painted Lady all increasing dramatically in abundance since the 1970s. In the last few years, rarer migrants traditionally only found in hotter climes, including the Long-tailed Blue, and European Swallowtail, have also arrived in southern England.

Thanks to an army of passionate lepidopterists, butterflies are currently the UK’s best-studied insects. A pair of citizen science projects – the UK Butterfly Monitoring Scheme (UKBMS) and Butterflies for the New Millennium – have respectively been measuring butterfly species occurrence and abundance involving tens of thousands of volunteers across the country, so the picture isn’t bleak everywhere.

 

- Peter Holthusen

Further information

Butterfly Conservation
UK Butterfly Monitoring Scheme (UKBMS)
Berks, Bucks & Oxon Wildlife Trust

 

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