Pearl-bordered Fritillary and Small Pearl-bordered Fritillary

The Pearl-bordered Fritillary (Boloria euphrosyne) is a striking, yet threatened, orange-and-black butterfly, often considered an early sign of spring in woodlands. It is known for being the first of its type to emerge, usually appearing in April. 

Here are some interesting facts about the Pearl-bordered Fritillary:

• Underwing "Pearls": The butterfly is named for the distinct row of seven white "pearls" along the outer edge of its hindwings, which are complemented by two larger silver, pearly patches closer to the body.

• The "April Fritillary": It is one of the earliest fritillaries to emerge, sometimes on the wing in late April to early June.

• "Bracken-loving" Caterpillars: The caterpillars thrive in sunlit, dry bracken or leaf litter, which can be up to 20°C warmer than nearby grassy areas. They overwinter wrapped in a leaf, emerging in spring smaller than when they went into hibernation.

• Declining Status: Once very common, it has suffered a dramatic decline in Britain—nearly 64% in abundance and 88% in distribution from 1976–2019, making it one of the most threatened butterflies in England and Wales.

• Habitat Specialist: They are known as a key indicator species for well-maintained, open woodlands. They prefer sunny woodland clearings and rides that have been managed by traditional methods like coppicing.

• Adult Diet: As adults, they are opportunistic feeders that love nectar from flowers like Bugle, Bluebell, and Dandelion.

• Identification Challenges: They are often confused with the Small Pearl-bordered Fritillary. A key differentiator is that the Pearl-bordered has a reddish chevron above its white "pearls," while the Small Pearl-bordered has black markings.

• The "Pearl Hotel": Due to their endangered status in certain areas, conservationists have used captive breeding programs, nicknamed the "Pearl Hotel," to rear caterpillars on sterilized, washed, and microwaved violet leaves to protect them from disease.

• Short Lifespan/Range: Individuals rarely travel more than 1km in their lifetime, making them very vulnerable to habitat fragmentation. 

The Small Pearl-bordered Fritillary (Boloria selene) is a declining, medium-sized orange butterfly known for the mosaic of white, orange, and black "pearls" on its hindwings. They prefer damp habitats, such as marshy grassland and woodlands, where their caterpillars feed exclusively on violets. Adults fly with a distinctive low, flutter-and-glide pattern. 

Key Facts about the Small Pearl-bordered Fritillary

• Distinctive Underwing: It can be identified from its close relative, the Pearl-bordered Fritillary, by the smaller black dot in the center of the underside hindwing and a row of white pearls, which are often bordered by black chevrons.

• Declining Status: While still locally common in Scotland and Wales, this species has suffered significant declines in England due to habitat loss.

• Habitat Specialist: They are usually found in damp, grassy habitats, including moorland, marshes, and woodland glades, notes the North Wales Wildlife Trust.

• Caterpillar Food: The caterpillars rely entirely on violets, specifically the Common Dog-violet (Viola riviniana) and Marsh Violet (Viola palustris).

• Unique Hibernation: The caterpillars have a unique life cycle, where they hibernate for almost an entire year before pupating, according to the YouTube video "Endangered Butterfly facts: Small Pearl-Bordered Fritillary...".

• Short Flight Period: Adults are typically on the wing from late May until July, stopping often to nectar on flowers like bugle and thistle.

• Geographic Variation: In southern England, they can sometimes produce a second brood due to earlier spring emergence.