Dark Green Fritillary (Argynnis aglaja)
Peak District local information
When to see: July-August
Where to see: Limestone grassland and moorland
Caterpillar food plant: Violets (Viola spp.)
Peak District status: This large, attractive butterfly is the only species of fritillary that still occurs in the Peak District. It is widespread in the White Peak , which represents something of a regional stronghold for the species, though colonies are scattered and usually small. It is seen annually in most of the major limestone dales and more sporadically in some of the smaller dales and elsewhere across the White Peak . It prefers areas of unimproved limestone grassland where the sward is relatively short, up to about 15cm, and contains sufficient quantities of violets (Viola spp.) the larval food plant.
Individuals are occasionally also seen in moorland areas where it has been recorded at several places, including Lady Clough below the Snake Pass and at the head of the Longdendale Valley in the north of the Peak District. One of its larval food plants, Marsh Violet (Viola palustris) grows commonly in moorland flushes and although breeding in these habitats has not yet been proved it remains an intriguing possibility.
It is usually seen in single figures but some colonies contain 20-50 individuals, though numbers fluctuate from year to year. The overall population is still relatively small. It emerges in late June or early July and remains on the wing throughout July to mid-August. It may persist until the end of the month and has been recorded as late as the beginning of September.
It is a strong flyer and the most common view is of it sweeping over dalesides in search of females or egg-laying sites. It can be approached more closely when nectaring on thistles or other plants. At such times it may reveal the underside hindwing pattern of pale green with silver-white spots. Females are a little larger than males, their wingspan reaching 69mm.
Most dark green fritillary sites lie within the Derbyshire Dales National Nature Reserve, Derbyshire Wildlife Trust nature reserves, Plantlife’s Deep Dale reserve and/or Sites of Special Scientific Interest (SSSI) and so receive some form of protection. Limestone grassland is a national priority habitat under the UK Biodiversity Action Plan and a considerable amount of effort is invested in conserving and extending the area occupied. This involves removal of invasive hawthorn scrub and optimising grazing regimes to maintain short, species-rich swards. These will promote growth of violets and should conserve suitable habitat for the dark green fritillary. This work is funded and carried out by several agencies including English Nature, Peak District National Park, Derbyshire Wildlife Trust and the Countryside Stewardship Scheme.