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14 Jun 2021

Burg’s beautiful slender Scotch burnet moth

Written by Emily Wilkins, Ranger – South Mull, Iona, Burg and Staffa NNR
A moth, with black and red colouring, is among long grass.
At first glance, Burg is all about the large scale – a dramatic coastline with towering cliffs home to soaring birds of prey, red deer and the huge imprint of a fossilised tree. Look more closely though and you might be lucky enough to spot some of its tiny treasures, including miniature alpine plants and the beautiful slender Scotch burnet moth.

If your first impression of moths is damage to clothes, or dull creatures that only fly at night, think again! Many of our moths are brightly coloured and some, including the group known as burnets, are day-flying.

Burnet moths use nature’s warning colours of black and red to inform any potential predators that they’re poisonous, so they have no need of camouflage. Amazingly, they’re able to absorb these toxins from the plants they eat as caterpillars. All species hibernate as caterpillars in the winter, waking up in spring to pupate into an adult moth, which will lay eggs to continue the cycle of life.

You may be familiar with the common six-spot burnet moth (Zygaena filipendulae stephensi), but several other species are among the rarest insects in the UK. Living in small, widely dispersed colonies means that subtle differences in wing pattern and habitat requirements have emerged.

At Burg we’re privileged to have a population of the slender Scotch burnet moth (Zygaena loti scotica) living in the coastal grasslands. This very rare moth is found only here and a few other places around Mull and the nearby islands of Ulva and Gometra, but nowhere else in the British Isles.

Close-up of the slender Scotch burnet moth, showing its red and black colouring.
The slender Scotch burnet moth

The National Trust for Scotland has looked after Burg since 1936. It was initially run as a demonstration farm, showing new techniques for bracken clearance and other ideas to make farming more viable in such a marginal location. In more recent times we have recognised the importance of the special wildlife, as well as the cultural heritage, geology and landscape views. Grazing by sheep and cows, along with wild red deer and feral goats, is carefully managed to keep all habitats in good condition.

The slender Scotch burnet needs a very specific combination of south or south-west facing slopes with short, flower-rich grassland. Rockfalls from the cliffs above and animal hoofprints create bare patches of soil where the moths can bask in the sun, absorbing energy for flight, while the right level of grazing ensures there will be plenty of the caterpillars’ favourite foodplant – common bird’s foot trefoil. We also use people power to remove bracken from the slopes, allowing a wide range of flowers to flourish, providing nectar for the adult moths. Some of their preferred nectar plants include milkwort, cat’s ear and wild thyme.

Every year, adventurous volunteers help us to monitor the moth population by walking in lines across the slopes, counting any moths they see. This is a specialist task, not only requiring the ability to walk steadily over steep ground, but also to distinguish from a blur of red and black wings whether you’re looking at a common six-spot, less common transparent, or rare slender Scotch burnet! We then report our findings to a group of scientists who oversee burnet moth conservation in the UK and around the world.

A line of people walking across a steeply sloped landscape surveying for moths.
Volunteers moth surveying

You might be wondering, why all this effort for a tiny, seemingly insignificant creature? Every species is just one piece of the rich diversity of nature, often with an important role to play (such as pollination) that we may not recognise until it’s lost. Managing our coastal grasslands for the benefit of our moths means a beautiful patchwork of colourful flowers with jewel-bright insects flying amongst them. Visit in mid–late June for the best chance of seeing the slender Scotch burnet, as it’s only on the wing for a few short weeks each year.

Two red and black slender Scotch burnet moths among wildflowers and long grass.
Slender Scotch burnet moths (image: Lindsay Mackinlay)

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