Large blue butterfly, Golden Valley, Stroud, Cotswolds

See conservation in action in this beautiful valley, home to one of our rarest native butterflies, says Julia Bradbury

3rd October 2013

Deep in the steep, green-sided valleys of the Cotswolds near Stroud is a magical place – the Golden Valley. It’s all green really, but what’s a little poetic licence when you’re surrounded by such beauty?

And threading its way through the Golden Valley is the Golden Valley walk: a short five-mile circuit that takes in some truly stunning landscape.

When I was there two years ago, it wasn’t for a hike. I was there to meet a man about a butterfly – the large blue butterfly, to be precise. This species flies from mid- to late-June and butterfly enthusiasts make an annual pilgrimage to a variety of secret locations around the area when season and landscape come together.

This butterfly is the largest and rarest of the blue butterfly species in the UK. Declared extinct in Britain more than 30 years ago, it is now the focus of a massive conservation effort to bring it back. In Northern Europe, it has been almost totally wiped out for a variety of reasons. They have a highly unusual lifecycle and require a perfect set of conditions to thrive. Intensification of agriculture during the 20th century led to a decline of rough hillside grazing, which creates the definitive habitat, while the introduction of artificial fertilisers that promote vigorous grass growth hasn’t helped the large blue either, because small wildflowers such as thyme suffer. No thyme, no large blues. 

There is another ingredient that is crucial to their lifecycle; a species of ant called Myrmica sabuleti. Scientists discovered that the large blue caterpillar hatches on thyme buds and then tricks the ants into believing it is one of their own grubs. Ants then carry it underground to their nest, where it feeds on the ant grubs for 10 months before pupating and emerging as a butterfly. What trickery.

I met research ecologist David Simcox, expecting to find a man with a net – instead he was busy laying out crumbs of cake to lure ants to the surface for an identity parade. We’d already detected wild thyme on the hillside, now we had to check that we had the right species of ant.

This landscape has been specifically managed with the help of the National Trust and local landowners for the large blue butterfly, and has been grazed by cattle and ponies at specific times of year. It is vital to keep it grazed in spring to counter the main pulse of grass growth.

It’s all about the vegetation; the ants thrive in short, acid grassland on hot, south-facing slopes. If the grass is allowed to grow tall, the ants rapidly die out and other species of ant, which cannot support large blue colonies, take over.

The ants came out to play and David confirmed they were what we were looking for – now all we needed was a butterfly. I have to admit, I thought our chances were slim.

Even though the sun was radiating through the Golden Valley, the air was heavy with the threat of rain and then we’d have no chance.

As well as managing the landscape for the return of the large blue, the other impressive aspect of this project is the harvesting, incubating and transplanting of hundreds of the eggs around several sites in the UK – by hand. Back in 2000, David was very busy in our location re-seeding hundreds of blue larvae introduced from a population in Sweden. This is one of the longest and most successful conservation projects for an insect anywhere in the world.

After I’d munched on some of the ant cake, we got down to the serious business of butterfly spotting. This is, surprisingly, not easy. You’re so desperate to see your target that anything with wings becomes ‘it’. I incorrectly identified a blackbird, a harrier jet and a deerstalker hat.

I’m not sure how you get your eye in for something you’ve never seen but suddenly David let out a cry, “there!” and one landed right beside us in a low level bush. My first large blue – a great thing to tick off anyone’s list.

Useful Information

The large blue colony is at Daneway Banks Nature Reserve and is best visited between mid-June and mid-July. Take the A419 from Stroud to Cirencester and turn left at Chapman’s Cross. Turn left at the crossroads for Sapperton and park in the layby at the bottom of the hill. Cross the canal bridge to enter the reserve. The reserve can also be reached on foot from Stroud (about five miles) by following the River Frome and the Old Severn-Thames Canal.

Tourist information
01386 837553

Sorrento Italian Restaurant
Russell Street, Stroud
01453 766 632
This friendly restaurant is a family-owned local favourite.

The Lockkeeper’s café
and bar
Wallbridge, Stroud GL5 3JS
01453 757 772
This arty, relaxed café offers great food. It hosts exhibitions and performances.

Dr Jenner’s House
and Garden
The Chantry GL13 9BN
01453 810631
Find out more about the famous doctor’s life and see the place where he developed the smallpox vaccine – a great family experience. 

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