If you go down to the woods today, you’re sure of a big surprise. And I don’t mean the hordes of humming mosquitos, ready to pounce on the unwary visitor whose mammalian blood they greedily seek…

silver washed fritillary caterpillar by Kevin Radley

Keep your eyes out for these spiky fellows, by Kevin Radley

To escape such unwanted attention, it has been recommended to avoid the use of perfumes, deodorants and soap. After trialling this remedy for a few days, I soon came to realise that it works well at keeping people at bay too (not so much the flies). Throughout high summer, it is worth braving the woods to enjoy the profusion of wildlife that dwells within (honestly, the mosquitos aren’t that bad).

Over the past few winters, the Wheatfen volunteers have been undertaking the ancient practice of hazel coppicing, as well as thinning out non-indigenous tree species. This allows the woodland floor to bathe in the sun’s warmth, encouraging many flower species to flourish. Rambling bramble, which thrives in these suntraps, has slithered and clambered over log and brash piles, forming tangled walls of thorny chaos. When its delicate, pale pink and white blossom erupts through late June, July and August, a plethora of invertebrate species indulge on its nectar, including one particularly showy butterfly.

Valezina silver washed fritillary by Ann kerridge

Valezina form silver washed fritillary, by Ann Kerridge

Absent from the reserve for over 7 decades prior, silver washed fritillary populations on site have exploded of late. Bright, golden-orange males showcase their size and flashiness as they patrol the pathways, charging along in a zig-zag fashion, searching for the duller-tinged females. Both have sooty coloured spots peppered across their wings. Additionally, the males are slightly smaller and have four black veins (sex brands) on their forewings. On the underside these butterflies earn their name, displaying beautiful, watercolour-washed, silvery streaks that are finely blended with greens.

Not all females adhere to the aforementioned patterning. This year, a rare colour form named Valezina graces the woodland (see Ann’s incredible photograph above). This elusive, dusky, green-tinted fritillary lurks in the dappled shade, skulking low to the ground; a frustrating tease for the keen, salivating naturalists who are hoping to catch a glimpse of this rare beauty.

silver washed fritillary by ann kerridge

A male silver washed fritillary, by Ann Kerridge

Observing the mating ritual for these butterflies is like watching some fine ballet performance; the female flying elegantly, straight and true, the male circling enticingly round and round her, spraying her in a confetti of scented love scales from his sex brands. Once mated, the females can be seen searching the woodland floor, locating the food plant of their caterpillars – dog violets. Oh yes, this butterfly is yet another fussy species on the reserve that does not really help itself; its very existence linked precariously to the abundance of the violets, and therefore the woodland coppicing and thinning. Mated females will lay their eggs on nearby, often north-facing tree trunks approximately 1- 2m above the ground. They crawl, crab-like up the trunks, probing their abdomens into fissures within the bark; the perfect microclimate for the eggs, also offering some protection from predation. Tiny caterpillars will hatch out after 2-3 weeks, hungrily devouring their eggshell. They then spin a pad of silk on which they hibernate, still on the tree stem. Not a bad way to spend the winter (although I think I would like to have eaten a bit more first).

During the warming days of March and April, the caterpillars awaken and do the equivalent of a big yawn and rub of the eyes, before romping down the tree trunk in search of the nearby dog violets. This is quite a journey really for something so small.    

silver washed fritillary close up

Getting up close and personal, by Ann Kerridge

Annoyingly, many of these violets grow perilously close to the grassy footpath. Mowing the grass has never been so challenging. After a few weeks of nibbling away on tender violet leaves and mower-dodging, these fattened caterpillars go on their last march to pupate nearby on a shrub or tree twig. At this stage their chrysalis resembles an old, dried leaf, ideally camouflaged to avoid predation. They start to emerge as butterflies in late June, completing the cycle.

At Wheatfen we are lucky; as one wave of iconic butterflies – those impressive first-brood swallowtails – finishes on the fen, another takes its place in the woods. But can a bog-standard silver washed fritillary really rival the mega star of the reserve, the swallowtail? Perhaps not… but the charming Valezina form just might!

Will Fitch

Author Will Fitch

I have been the Warden at Wheatfen for a number of years now, helping to look after and manage the reserve with the help of our trusty volunteers. You can often find me either out and about at the reserve, or in the Warden's hut in the car park.

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