These are very exciting times in the history of the Large Blue in the UK our butterfly specialist Matthew Oates explains.
Conserving the Large Blue:
- The Large Blue 'Maculinea arion' is the only British representative of six species of large blue butterflies globally, five of which occur in Europe. All six are in serious decline and classified as either endangered or vulnerable at global and European levels.
- Large blue butterflies as a whole can be ranked amongst the most vulnerable species in the world.
- In Europe, the Large Blue 'Maculinea arion' still occurs in 37 countries but it has declined by some 50-80 percent in recent decades overall and is deemed stable in only seven countries.This decline is particularly severe in Northern Europe.
- A massive amount of effort is being made to save all the European specials of large blues, led by scientists from a number of countries.
The Large Blue Recovery Programme
In the UK, the Large Blue Recovery Programme is a partnership made up of, at present, 23 organisations and individuals including Oxford University, the Centre for Ecology & Hydrology (formerly ITE), English Nature, Butterfly Conservation and the Wildlife Trusts for Gloucestershire and Somerset, and of course the National Trust.
The partnership seeks to further the conservation of the Large Blue in the UK and, in particular, to re-establish the butterfly at suitably-managed sites in England. It is led by Professor Jeremy Thomas of Oxford University and David Simcox of CEH, who works as the Large Blue Porject Officer.
The Large Blue season
- In the UK, the Large Blue adult season lasts for some three or four weeks during June and July.
- The timing of the flight season varies from site to site, region to region and from year to year, with much depending on seasonal weather.
- Individual Large Blue butterflies live for four to five days, on average, but they do not all emerge at once; individuals tend to emerge over a period of 10 to 20 days.
Young Large Blues
- The female Large Blue lays her eggs in the buds of thyme, before the flowers open. This necessitates full synchrony between the bud stage of the thyme and the butterfly’s flight season; this synchrony is assisted by appropriate grazing.
- The eggs hatch after some seven to 14 days, depending on the weather. Young larvae feed on thyme flowers for about two weeks during late July and early August. Then, they fall to the ground and are adopted by red ants and taken off to the underground ant nests where they feed on ant grubs.
- Any species of red ant may pick up the caterpillars, which secrete a sticky sugary substance that ants love. But in the UK, the caterpillars survive only in the nests of a single ant species, 'Myrmica sabuleti'.
- Frequent and large nests of this single species of ant are essential to the Large Blue.
- The larva spends 10 months as a predator in the ant nests, then pupates there.
© J A Thomas
M. sabuleti is a warmth-loving ant that thrives in short, arid grassland on hot south-facing slopes that are usually heavily grazed.
If the grass is allowed to grow tall ant rapidly dies out and other species of ant take over, which cannot support Large Blue colonies. Ant density is also adversely affected by cool, wet summers and spring droughts.
The butterflies emerge during the period early-June to mid-July, after some three weeks in the pupal stage.
Adult numbers tend to vary enormously at individual sites from year to year, as a result of the impact of seasonal weather on the habitat and the weather-sensitive ants, and as a result of habitat conditions generally, especially the grazing regime.
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Secret ‘Site X’
The last site to support the UK race, and the first site to receive introduced Swedish Large Blues, is on National Trust land in South Dartmoor. It is kept as an open secret and is known within butterfly circles as ‘Site X’. It was here that Jeremy Thomas determined the full ecology of the Large Blue, sadly as the butterfly was dying out (it was declared extinct nationally in 1979).
The Large Blue was experimentally reintroduced here in 1983, and once this proved successful a full reintroduction took place in 1986.
Grazing by cattle and ponies is the main conservation action here. This grazing has to take account of fluctuations in the rabbit population, an added complication.
Clumps of gorse are burnt on a patchy rotation, to provide the warm sheltered glades and mosaic structure that the butterfly needs and to prevent the gorse from taking over.
Bracken is highly invasive here and has to be carefully managed, though managed, through modest amounts provide good habit for four species of fritillary butterfly here.
© National Trust
'Site X' is perhaps too small to sustain a permanent Large Blue population by itself, and the main challenge for the Large Blue Project here is to enlarge the area utilised by the butterfly and establish a metapopulation (clusters of loosely-connected colonies) structure.
To date, the habitat quality on 'Site X' has been greatly improved and the adjoining hillside, 'Site Y', has been made more suitable.
A range of other scarce animals and plants (including two of Britain’s most rapidly-declining species: high brown fritillary and pearl-bordered fritillary) have benefited from the grazing and gorse-burning that is primarily aimed at assisting the Large Blue. 'Site X' is not just an example of ‘single species management’.
The main challenge now is to continue to extend the area of suitable habitat and to seek to restore comparable habitat within the wider landscape. We hope to promote low key access to this wonderful butterfly site within the near future.
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Other Large Blue sites
The National Trust has been associated with attempts to conserve the Large Blue since the 1920s.
Many of the 90 or so colonies that have existed in England occurred on land now owned by us, especially along the North Cornwall coast. The butterfly had died out from nearly all of them prior to Trust acquisition.
In 2000, the Large Blue was introduced to a large and very remote sea combe we own on the North Cornwall coast, well north of Port Isaac. A small but viable population has become established here, thanks to the dedication of Derek Lord, the warden, and his team of staff and volunteers. Access is hard to promote, not least because it is impossible to park within 2 miles of the combe.
We are also working hard to return the Large Blue to another combe on the North Cornwall coast, close to the Devon border. This combe, called the Tidna, was purchased as a reserve for the Large Blue and donated by the late Malcolm Spooner, an eminent entomologist who tried hard to save the butterfly from extinction. The Large Blue will soon return here and low key access will be facilitated once the population is secure.
For the time being at least, the Trust is encouraging people to visit Collard Hill, though we do intend to facilitate access to other sites shortly. Watch this space! Both are currently open secrets.
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Collard Hill, the place to see Britain's rarest butterfly
The Large Blue has been brought back from beyond the brink of extinction. It wasn't easy: it took a lot of hard work by a dedicated partnership of diverse organisations, backed by some of the best conservation biology research ever conducted, anywhere.
© Matthew Oates
The National Trust is particularly keen on helping the Large Blue Recovery Project by providing sites for scientific research and especially for public access, ideally both together.
Collard Hill was set up as an open access site for the Large Blue. Twelve females and three males were released there in late June 2000, and 267 larvae were introduced in late July. It was not possible to open in 2001 due to foot and mouth disease, but has been open ever since.
Running the open access site is quite challenging, and requires a dedicated team of wardens, led by senior warden Rob Holden, a seasonal Large Blue warden who is employed for some 6 weeks, annually, and a team of volunteers from Butterfly Conservation.
The all important grazing is delivered by a local farming family, who also provide accomodation for the Large Blue warden.
The site is grazed by cattle and ponies, at specific times of year. It is vital to graze quite hard in spring, to counter the main pulse of grass growth and promote healthy ant populations amongst short grass. We have not always got this right, but have now hit on a system that works. The critical move was installing a fence along the crest of the slope, which meant we can run stock on and off the slope as required.
Furthermore it is part of a network of potential and actual Large Blue sites within the Polden Hills landscape, much of which is under positlve management by a range of conservation organisations.
This site is part of an attempt to re-establish the Large Blue butterfly by establishing an extensive metapopulation structure at landscape level.
Furthermore, it is part of a network of potential and actual Large Blue sites within the wider Polden Hills landscape, much of which is under positive management by a range of conservation organisations.
This site is part of an attempt to re-establish the Large Blue butterfly by establishing an extensive metapopulation structure at landscape level.
Already, some natural spread and colonisation has been noted in the Poldens, a wonderfully healthy sign.
Collard Hill is the only place in Britain where people are freely able to visit to see this incredibly rare and special butterfly. The Trust has dedicated this hillside to the conservation of the Large Blue and people’s engagement with this most curious of insects.
The site exists for everyone, for ever; so come this year, next year, sometime, whenever. The Trust aims to keep the Large Blue at Collard Hill for as long as is practically possible.
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© Matthew Oates
We run a Large Blue phone line – 01793 817732 - from early June to mid-July. It provides information on how to see the Large Blue at Collard Hill.
The message is updated regularly, particularly before weekends. Information is given on the state of the flight season, as well as parking, access and health and safety arrangements.
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