Large Blue Butterflies: Back from Extinction

Large Blue Butterflies (Maculinia Aryon)

Large Blue Butterflies (Maculinia Aryon)

The successful reintroduction of the Large Blue butterfly into England after becoming extinct has many lessons for scientists and conservationists.

Large Blue Butterflies (Maculinia Aryon) became extinct in the UK in the 1979. It is now the UK’s most successful butterfly after being reintroduced and shows how scientists and naturalists can work together to protect our environment and endangered species.

Professor Lord May of Oxford, recent President of The Royal Society and former Chief Scientific Adviser to the UK Government, said last year on the 25th anniversary of the butterfly’s reintroduction: “The recovery of the large blue butterfly is the world’s largest-scale, longest-running successful conservation project involving an insect. It illustrates perfectly how the application of sound science can be used to solve some of the apparently intractable problems that face conservationists worldwide today.”

The strange life cycle of the Large Blue butterfly

Over the past century, attempts were made to halt the decline of the species but with no success. The problem was that while caterpillars could be raised from eggs, they kept dying before they reached the pupa stage.

Eventually, scientists discovered that the large blue butterfly had a rather complicated life cycle – in fact it depended on being nursed by a particular species of red ant (Myrmica sabuleti).

The adult female butterfly lays eggs on purple thyme plants. The eggs hatch and the caterpillars grow on the purple thyme, eating away. But before they reach the pupa stage they fall from the flower. On the ground the caterpillars emit a sweet fluid and mimic the larvae of red ants. The ants are attracted and mistaking the caterpillar for one of their own larvae, they take it into the nest. There the red ants raise the caterpillars feeding them on red ant larvae. In the summer, the young winged butterfly emerges form the ants’ nest.

Butterfly larvae call to red ants

One of the strangest aspects to this strange story is that the butterflies actually “call out” in the nest to the particular species of red ants, mimicking the sound of other ants. You can hear it here and read more on the Large Blues.

So it was necessary to find areas where Myrmica sabuleti lived and to find a sub-species of Large Blue which would drop the to the ground at the right time of day when the ants are above ground and can find it. One sub-species of butterfly was found on a Swedish Island.

The right habitat

A further problem was that so many grassland habitats were changing and becoming unsuitable for the butterflies. Either they were being ploughed or turned into very short grassland or allowed to grow wild where the grass would be too tall for ant and butterfly alike.

So the National Trust along with various other agencies started to manage selected areas in ways most conducive to the large blue’s lifestyle: this involved some grazing (but not too much), control of trees and bracken and encouraging the growth of purple thyme.

“Getting the habitat in the right condition for this very particular butterfly had been crucial, and has been down to getting the grazing right – using cattle and Dartmoor ponies,” said Rob Holden, the National Trust’s area warden at Collard Hill.

Collard Hill in Somerset is the only one of 25 sites in Southern England that is open to the public. Large Blues were re-introduced to the site in 2000 with just over 250 larvae, this year more than 1,300 adults were spotted flying. The site is flourishing so well that eggs from it are being used to populate other sites.

The work of scientists in identifying the life cycle and conservationists in creating habitats where the butterflies may flourish means that the Large Blue reintroduction has been one of the most successful project of its kind in the UK. Globally, the UK is the only country where Large Blue’s are actually increasing in terms if numbers and sites.

Spotting Large Blue Butterflies

Despite the name, Large Blues are not that large, about two inches across and only slightly large than the male Common Blue, for which it is most often mistaken (female Common Blues are actually brown on top so it is only the males that confuse). Large Blues also fly for a shorter period, usually late June and early July.

The Large Blues have black spots on the forewings and the blue is sometimes described as being iridescent or steel-like but lighter than some of its counterparts. They fly in what is often described as a “drunken” manner.

I took a trip to Collard Hill last year in early July (where I took the accompanying photos). The warden was there along with several others who were all helpful in identifying Large Blues (the site also has Common Blues along with many other fauna and flora and great views). We saw nothing for the first two hours but as the day brightened up out came the Large Blues. I saw so many in one particular area that one would think they were common species rather than something that had risen from being extinct. And that is a testament to the hard work of all those involved in its reintroduction.


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