Incredibly rare and surprisingly swift. Britain’s most endangered butterfly can be found zooming at high speeds across woodland clearings, seeking out snug sanctuaries in bracken for their young.
Common name: high brown fritillary
Scientific name: Fabriciana adippe
Family: Nymphalidae
Habitat: coppiced or open woodlands with bracken and violet, limestone rock areas
Predators: birds, small mammals and other predatory invertebrates
Origin: native
Caterpillars: have brown, spiny bodies with one long white stripe down the middle, flecked with black markings. They look remarkably similar to the dead bracken they bask on.
Adults: have large, bright orange upper wings with an intricate pattern of black spots and dashes. The underside of the hindwing features distinctive orange-ringed silvery pearls.
Wingspan: 60–67mm.
Caterpillars: depend entirely upon violets. While common dog-violet is a favourite, these picky eaters have also been known to feed on heath and pale dog-violet, while in limestone rock areas they will munch on hairy violet.
Adults: have more varied tastes and mainly nectar on the blooms of bramble and thistle, but will also consume knapweed, ragwort, betony and wild thyme.
Male high brown fritillaries charge across wide areas in search of a suitable mate, often in the late morning. While patrolling, they will inspect any brown object that could be a female.
Females lay tiny eggs in areas offering a mosaic of bracken and common dog-violet. The apricot-hued eggs tinge to grey as the larva develops over the winter. Once hatched, caterpillars devour the tender leaves of dog-violets and bask in the sun, perfectly camouflaged among the bracken. After nine weeks, they spin leaves together into a loose tent, inside which they form a dark brown pupa that looks just like a shrivelled leaf!
Though once widespread across England and Wales, high brown fritillary populations have declined dramatically since the 1950s. They now exist at just one site in Wales and have several key strongholds in England, including Dartmoor, Exmoor and the Morecambe Bay Limestones. These elusive insects favour coppiced or open woodlands which provide lots of light and offer bracken and violet.
Bracken’s tangle of fronds and stems offers a toasty microclimate up to 20°C warmer than its surroundings. It’s a little like nature’s greenhouse!
High brown fritillary butterflies are on the wing from June to August. This extremely rare species is difficult to spot and is easily mistaken for the dark green fritillary butterfly (which lacks the orange-ringed silvery pearls on the underside of the hindwing).
You are most likely to see females when they are ready to lay eggs, as they flutter low over the woodland floor in search of the foodplant of their young: violets.
You won’t see them by night or during dreary weather, as these butterflies seek shelter by roosting in the treetops.
Since the 1970s, this formerly widespread butterfly has been reduced to 5% of its former range and exists at just 50 sites. The high brown fritillary largely depends on coppiced woodland and grazed bracken habitats, so a reduction in traditional coppicing and grazing practices has contributed to plummeting populations. It is now considered the most threatened butterfly in Britain.
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Amy Lewis • 22 Jul 2019
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