UK’s Large Blue butterfly rewrites record books…again

COMEBACK: The beautiful Large Blue Picture: CNTPL / Ross Hoddinott

June 2010: One of the greatest British wildlife success stories of the past 30 years, the reintroduction of the Large Blue butterfly, had a record-breaking year during the 2009 flight season at the National Trust's Collard Hill site near Glastonbury in Somerset.

Naturalists are hoping that as the 2010 flight is due to emerge, the weather this year will help break new records.

Detailed surveys estimated that more than 20,000 eggs were laid in the last flight season and that around 800 butterflies emerged and flew on the site. This was an increase of 22 per cent on 2008 figures which had also been a record year.

Rob Holden, National Trust Area Warden, said: ‘The past four years at Collard Hill have seen a steady but strong increase in the number of Large Blue butterflies recorded.

Carniverous caterpillar's con-trick
Collard Hill is the only easily accessible place - that is open throughout the year - where visitors can see this jewel of a butterfly. The Large Blue's flight season lasts for around a month and the National Trust holds an open day in late June to celebrate the project.

The Large Blue begins life as a normal caterpillar and the young larvae feed on wild thyme flowers. From then on, its life depends on an elaborate trick. As each larva drops to the ground, it secretes a sticky sugary substance which ants can't resist. The ants are, in fact, tricked into thinking that the larva is a lost ant grub and take it into their underground colony.

BUMPER YEAR: But this butterfly had been declared extinct in 1979. Picture: NT / Ross Hoddinott

An incredible phase in the caterpillar's life then begins where for ten months it turns into a carnivore - feeding as a parasite on the ant grubs having conned the hapless ants into thinking it is harmless. The caterpillar then pupates in the ant nest, and the butterfly crawls out of the ant tunnels finally emerging for a few brief days in the last stage of its remarkable life as a beautiful butterfly.

Last year was the 25th anniversary of the re-introduction of the Large Blue into the UK after it had been declared extinct in 1979. Since then great progress has been made and there are now some 25 Large Blue sites in South-West England including Green Down managed by the Somerset Wildlife Trust.  The Large Blue was re-introduced to Collard Hill in the summer of 2000 and the first successful flight season was 2001.

Aa bumper year
Rob Holden continued: ‘With a large number of eggs laid during 2009 we're hoping for a bumper year. It will come down to getting the grass at just the right length and much depends on the good old British weather.'