The pearl-bordered fritillary (Boloria euphrosyne) is a butterfly of the Nymphalidae family found in Europe and northern Asia.

Description

It is orange with black spots on the upper side of its wing and has a wingspan of 38–46 mm. On the underside of the wings there is a row of silver pearly markings along the edge, which give the species its name. It is often confused with the small pearl-bordered fritillary, but can be distinguished from it by the triangle along its pearl-border (the small pearl-bordered has black chevrons) as well as the presence of a single silver spot in the middle of a row of yellow spots. The female has both darker markings and rounder wings than the male. The caterpillars are black with white or yellow spines along their backs.

Like other species of fritillary, the males have special scent glands on their wings so that they can be recognised by females of their own species and therefore find a suitable partner.


Dorsal side


Ventral side

Distribution

The pearl-bordered fritillary is widespread throughout Europe, ranging from Scandinavia to northern Spain and from Ireland eastwards towards Russia and Asia. In England and Wales (plus another 10 countries) it has declined rapidly in number and is a highly threatened species - nbn gateway distribution map.

Subspecies

B. e. euphrosyne – Central Europe, Siberia
B. e. fingal (Herbst, 1804) – Northern Europe, Siberia
B. e. rusalka (Fruhstorfer, 1909) – Southern Europe, West Siberia
B. e. orphana (Fruhstorfer, 1907) – Transbaikalia, Amur, Ussuri
B. e. kamtschadalus (Seitz, ) – Kamchatka, North Sakhalin
B. e. umbra (Seitz, ) – Altai, Sayan
B. e. dagestanica (Sovinsky, 1905) – Caucasus, Transcaucasia
B. e. nephele (Herrich-Schäffer, ) – Urals, Siberia
Foodplants and eggs

After mating, the female will lay her eggs on dead bracken (Pteridium aquilinum), or leaf litter near to violet plants – common dog–violet (Viola riviniana), heath dog–violet (Viola canina), marsh violet (Viola palustris). Sometimes they are laid on the leaves of the foodplant itself. They are laid singly, not in one large group such as the marsh fritillary. The mosaics that they prefer are typically one–third grass and two–thirds bracken.

Eggs can be found on the foodplant from mid–May to the end of June. They are a pale yellow colour and can hatch after 10–14 days.

Caterpillar, pupa, and adult

The emerging caterpillars begin feeding immediately and will moult three times within the first 5–6 weeks. Each caterpillar will then hibernate in a shrivelled leaf at the base of the plant, usually at the end of July. When they awaken the following March, they are half their previous size having shrunk during hibernation. After a period of feeding and growth, during which it moults one last time, the caterpillar is full size and ready to pupate. The chrysalis stage is formed amongst the leaf litter, and lasts just 10–14 days.

The adult butterfly flies between late April and June, being one of the earliest fritillaries to emerge. It will feed on the nectar from early spring flowers such as bugle, dandelion (Taraxacum officinale), and lesser celandine.

There is a second brood during August.

Habitat

Woodland clearings, recently coppiced or clear-felled, with bracken, or leaf litter provided by oak and bramble
Well-drained habitats with mosaics of grass, bracken, and light scrub
Hot and freshly cut material
Abundant foodplants growing in short, sparse vegetation, where there is abundant dead plant material, bracken is preferred
Scrub edges can provide good breeding conditions, e.g. gorse
Management

A network of paths running through bracken to open the canopy, allows sunlight through to help germinate any violet foodplants. This can be achieved through grazing especially during winter and early spring. Cattle are better than sheep as their extra weight helps to trample and break up any dense standing dead stems. Also there is a risk that sheep tend to eat plants, (for example Ajuga reptans/bugle), that provide nectar for the adult pearl-bordered fritillary. Another way of achieving this is by cutting and bruising the bracken, a proportion of the site at a time, during May and early June.
Burning can be useful for reducing the litter of bracken, although follow up management is required as extra bracken growth will be stimulated as a result. This will kill a proportion of invertebrates, and therefore only burning a proportion of the site, e.g., 20% is suggested.
Spraying can be useful for reducing high densitites bracken litter, but care should be taken to not severely reduce the density and allow the grass to develop, as this will harm the breeding habitat.
Woodlands create sunny clearings and rides, but avoid using clearings that are dominated by other plants such as dog's mercury (Mercurialis perennis), common bluebell, and vigorous grasses.
Example sites where found

Haldon Forest, Devon, UK
Lambert's Castle Hill, Dorset, UK
Hard Hills, Cornwall, UK grid ref SS 235176
Ireland
^ "Rare British butterfly expands into Devon forest". BBC. Retrieved 2016-01-28.
^ Nash, D.W. and Hardiman, D.M. (2013). A review of the Pearl-bordered Fritillary (Boloria euphrosyne L.) in Ireland. Ir. Nat. J. 32: 132 - 137.

source - Wikipedia