Large Blue butterfly - reintroduction into North Cornwall

The large blue butterfly Maculinea arion has a very specialised life cycle. The larvae initially feed on thyme flowers, but after a few weeks they fall off the plants and are adopted by a particular species of ant, Myrmica sabuleti. They spend the rest of their larval stage in the ant nest, feeding on the ant's own larvae, to emerge as adult butterflies in late June.

Formerly widespread on the south-facing Atlantic coastal valley slopes of Cornwall and Devon, from the Camel Estuary to Clovelly, the large blue became extinct here in 1975, and in the UK (on Dartmoor) in 1979. The principal reason for the extinction was the loss of the habitat of Myrmica sabuleti, which can only survive in the shortest turf (less than 2cm) of warm south-facing slopes. In former times the turf was kept short by farm animals and regular burning (a procedure known as swaling). Changes in farming practices led to the removal of domesticated animals, and swaling ceased. Initially, rabbits were still there to keep the turf short, but the advent of myxomatosis in the late 1950s removed this last grazing pressure. The grass grew and, within a few years, the ant was much reduced along with the large blue.

As a result of work carried out at the Institute of Terrestrial Ecology by Dr Jeremy Thomas and Dr Dave Simcox, the habitat at the last UK site was returned to a suitable state and the large blue was reintroduced in 1983, using stock from Sweden. Butterfly numbers at this initial site have increased year on year, enabling reintroductions to take place at several former UK sites where suitable management regimes are in place to maintain short turf for the ant.

After much hard work over the last six years by Derek Lord and his team at the National Trust, the first site in Cornwall was declared suitable for reintroduction the year 2000. On 27th June, ten egg-laying females and two males were released, and eggs were soon found on the thyme plants. Up to three hundred captive-bred larvae will also be released this summer. With around 25% survival rate, over fifty butterflies may fly in 2001. If all goes well, this will form a self-sustaining colony in future years, perhaps enabling other suitable sites to be repopulated. The following pictures were all taken on 19th July 2000.

Adrian Spalding (Secretary, Large Blue Committee), holding the box with the larva, and Lee Slaughter (Chairman, Cornwall Butterfly Conservation), with Dave Simcox (Institute of Terrestrial Ecology), making final preparations at the release site for the first large blue larva. The water sprayer is to moisten the release area, creating suitable conditions for the larva.

The tiny (3mm) fourth instar
large blue larva in its box

Dave Simcox about to release the first larva.
The ant nest can rarely support more than one larva, so each release area
is marked with a stick to ensure that they are well spread around the site.

Dave Land (Devon Butterfly Conservation)
filming the adoption of the larva.

Large blue larva wandering

Large blue larva being found
by Myrmica sabuleti

Malcolm Lee

Further information on the complex relationships between ants and Large Blue Butterflies can be found at http://www.zi.ku.dk/personal/drnash/atta/default.htm

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