Blog written by Tim Aldred

In April 1928, wealthy landowner and scientist Sir Charles Langham received news of a plague in Co. Fermanagh, Ireland. He rushed to the site of the outbreak—a remote field in Enniskillen—only to find that the locals had already taken matters into their own hands. They were burning the grass in a desperate attempt to eradicate a horde of caterpillars so vast that farmers were raking them up into huge piles. Some villagers had barricaded their homes with peat bricks, to protect themselves against the onslaught of larvae. Langham wrote: “it would be an exaggeration to say the field was black with them but not very far from the truth.” He rescued no fewer than 18,000 of the caterpillars that season, and reared them at his own home, where they restyled themselves into marsh fritillary butterflies. How differently, one wonders, might those Irish villagers have viewed the more delightfully dressed adults of the species?

The word fritillary means chequerboard, and you only have to see one of these butterflies to understand how the association arose. All the members of the fritillary tribe can be distinguished by a striking tessellation of golden orange and dark brown/black chequers on their upper wings. But the marsh fritillary has the broadest palette of all. Its chequerboard pattern also contains hues of cream, making it easily distinguishable from its peers.

Populations of marsh fritillary can vary greatly in size from year to year, following a boom-and-bust cycle. ‘Outbreaks’ such as the one recounted by Langham were a regular, albeit infrequent, occurrence in the nineteenth century (another example was recorded in Co. Clare by the Rev. S.L. Brakey, who observed caterpillars “so multitudinous in some fields that the black layer of insects seemed to roll in corrugations as the migrating hosts swarmed over each other in search of food.”)

But times change, and in the years since it reached plague proportions, the marsh fritillary has suffered an alarming reversal of fortunes. Today, it is listed by Butterfly Conservation as one of the most threatened butterfly species in the UK.

“A change in land management is one of the biggest reasons why marsh fritillaries have suffered such catastrophic declines,” says Ellie Jones, Reserves Manager for Wiltshire Wildlife Trust. Ellie is leading a new project to restore marsh fritillaries to Upper Minety Meadows - the Trust’s newly acquired reserve. On this especially sunny morning, she has invited me, along with a number of other volunteers, to join her for the first phase of that restoration work. When I arrive at the bottom of an uneven track that seems engineered to test the limits of my car’s suspension, I find Ellie flustered. A colleague who was supposed to meet her with a consignment of tools has broken down. But after a tense conversation or two, she’s arranged for some backup.

While we wait, I take in my surroundings. Given the ‘marsh’ part of the butterfly’s title, I feel entitled to expect a landscape of waterlogged soil, pricked by rushes, sedges and reeds. But what I find instead is pastureland, freckled with buttercups. As it turns out, the marsh fritillary is deceptively named. Whilst it does have a love for damp habitats such as boggy grasslands and wet heaths, it can also thrive in drier locations, including chalky hillsides and—in the case of one population in Northern Ireland—even on coastal sand dunes. Somewhat paradoxically, true marshland doesn’t seem to feature in the list of its known haunts.

There is one thing, however, that connects every site where marsh fritillaries are found: Devil’s-bit scabious. The name might be redolent of some unholy pox, but to the butterfly this plant is positively life-sustaining. Recognised by its pincushion-like balls of purple-blue flowers, it’s the preferred foodplant for marsh fritillary caterpillars. No scabious, no fritillaries. Simple as that.

The trouble, Ellie tells me, is that you only find devil’s-bit in fairly unimproved grasslands (in other words, areas that haven’t been heavily fertilised for agriculture). “As soon as you start adding excessive nutrients and fertilisers, you’re likely to lose the devil’s-bit,” she says objectively. And that’s not all. “The fritillaries are also quite fussy about the habitat they like,” Ellie explains. “They won’t tolerate hay cutting or overgrazing. Their ideal habitat structure is an uneven patchwork of short and long vegetation.”

As she talks, I start to understand why industrial agriculture and modern land management practices have taken their toll on this fussy fritillary.

Armed with knowledge of the species’ exacting requirements, Ellie hopes the Trust’s project will support the marsh fritillary’s long-term recovery. Late last year, an urgent appeal was issued to raise £49,200. This was the final amount needed to unlock £442,941 of funding from Biffa Award, a multi-million-pound fund that helps to build communities and transform lives by awarding grants to environmental projects across the UK. The appeal was a success, allowing the Trust to purchase 44 acres of land at Upper Minety in North Wiltshire.

About the Marsh Fritillary project

The land quadruples the size of the Trust’s existing nature reserve at Emmett Hill and will hopefully provide vital habitat for the marsh fritillary. A key part of the plan is the introduction of devil’s-bit scabious. And that’s we’re here today: to help plant it in strategic positions around the reserve.

Ellie is anxious to get started. There are 750 ‘plugs’ of devil’s-bit scabious in the back of her van, plus another dozen or so larger plants which she has grown from seed at home. But we still have no tools for the job. The morning is wearing on, and although it’s only the second day of meteorological summer, the sun is beating down on us as if it’s peak season. More volunteers arrive, smothered in sun cream, and Ellie delivers a quick safety briefing. Then, to the sound of a collective cheer, the cavalry shows up. Neil Pullen is Wiltshire Wildlife Trust’s Reserves Manager for the Swindon area. And he’s brought trowels and spades. 

With no time to waste, we head out to the first planting site, carrying our precious cargo of fritillary food. There’s no path to follow, so we wade through the waist-high sward of meadow foxtail and buttercup. Slender-bodied damselflies waft through the warm air, and I can hear swifts screaming in the neighbouring field. It already feels like this place holds promise as a future wildlife haven.

Ellie leads us to a patch of ground underneath an oak tree, which has been mown in a neat square (courtesy of Marie, one of the volunteers). Marie is a mature student studying British Wildlife Conservation, and spent yesterday mowing several patches of ground ready to receive the devil’s-bit.

Out comes the first tray of 150 plugs: each one a conical root mass some 3 inches deep, and bearing a small rosette of leaves. Putting these germinated plants in the ground will give them a greater chance of survival than sowing seeds. Each plug is valuable. Each one is potential food for a marsh fritillary caterpillar.

Unlike most other butterflies, marsh fritillaries are unusually sociable as caterpillars. After hatching, they crowd together in silken webs, which they drape over their foodplant. Inside the web, the larvae are protected as they feed and grow. Often, if they consume all available food, they move en masse to another plant.

After overwintering in a smaller, thicker web, tucked down in the vegetation, the larvae then emerge in February. Their black bodies soak up the spring sunshine, providing the energy they need to fatten up and pupate into their adult forms.

While banding together as larvae affords the marsh fritillary relative safety in numbers, there are some downsides too. Crowding increases competition for food, and makes the caterpillars easy targets for parasitic wasps, which lay their eggs in the soft-bodied larvae. In some years, the wasp incursions are nothing short of a blitzkrieg, leading to very high rates of caterpillar mortality. But at Upper Minety Meadows, the threat from wasps is of no immediate concern.

“The wasp is even more rare than the butterfly because it relies almost solely on marsh fritillaries,” Ellie explains.  “In the past, when there used to be swarms of caterpillars, they would eat themselves out of house and home. There’s an argument that we actually need the parasite, to stop them doing that, and to help keep things stable.”

One plug after another, under the green gaze of the oak tree, we impregnate the soil with devil’s-bit scabious. The earth here is rich with worms, grubs and the occasional click beetle. But it’s also hard and clay-like. I worry that the roots won’t take to it, so I do my best to loosen the soil around each hole, in the hope that it might form a more effective womb for the fledgling plants. I glance at the sky and wonder when the seedlings will get their first dose of rain. But the sun seems to have other ideas. And that’s okay. The seedlings need solar energy too, to coax their leaves into long, oval tongues. For that magic trick we call photosynthesis.

We work on our hands and knees, with meadow grass and wildflowers swaying above our heads. It’s not long before the first tray of plugs is safely in the ground, and we move on to the next patch – again, in the vicinity of an oak tree. There’s a pick-up truck sailing across the meadow from the opposite direction – a Hilux Invincible, driven by Jonathan Clarke, the Farm Manager. He’s brought more tools, including dibbers, which are eminently more suited for the task at hand. We all switch tools, and the work continues at a faster pace. In no time at all, we transplant the next 150 plugs of scabious, and then it’s time to stop for lunch. Ellie’s brought cookies and chocolate cakes for everyone. They’ve wilted in the heat, but are well-received nonetheless.

It feels good to be out in the fresh air, cradled on all sides by the flora of early summer. A buzzard circles in the sky and the clouds drift as slowly as thistledown. Seeing a marsh fritillary flit past would be the icing on the cake. According to Ellie, they used to be fairly regular in the area around Upper Minety Meadows. But then, in the mid-90s, they just disappeared. By itself, that information isn’t terribly surprising. Marsh fritillaries have gone extinct over large parts of their former range, having declined by about 60% since records began. But I was under the impression that south-west England (particularly Devon, Dorset and Wiltshire) was a stronghold for the species?

“Well, yes,” says Ellie. “In the south of Wiltshire, on the chalk download, marsh fritillaries are doing well. Or, at least, they’re holding their own. We have colonies on the Pewsey Downs, and a number on the plains south of the M4. But up here in the north, it’s a completely different story. That’s where ‘chalk and cheese’ comes from. It originated in Wiltshire. The north is the dairy land, or the cheese. And then the chalk’s in the south. We’re talking about two entirely different landscapes.

I turn this over in my head. The work we’re doing here today is not, as I thought, to boost an existing fritillary colony. Rather, we’re laying the foundations for the return of the butterfly to lands it’s all but forgotten. But wait. That’s no reason to be despondent. Last year, Ellie found a larval web at Emmett Hill, the small reserve which adjoins this land. And the last known colony only a few fields over from here. That means the new reserve is in an ideal location to reconnect those areas. “And it’s got the potential to be restored, that’s the important thing,” Ellie enthuses. “At the moment, we haven’t got any larval foodplants here. But what we do have is a really big area, and we’re going to manage it specifically for marsh fritillaries. And if we can restore the devil’s bit alongside other wildflowers, it should have positive implications for a load of other species as well.”

An exuberant song thrush provides the soundtrack to the final planting session; this time in a neighbouring field that feels decidedly more ‘marshy’. There’s a stream choked with fool’s watercress, and I can also see swathes of rush and a scattering of cuckooflower – both plants typical of damp habitat. We even see a frog hopping around in the field margin.

Ellie splits the team into pairs and dispatches us to separate planting zones. The idea is to divide and conquer. I plant with Jane, a retired teacher who now spends much of her time as a volunteer on local conservation projects. In February, Jane attended a training day hosted by Wiltshire Wildlife Trust, with the help of Dr Susan Clarke, a marsh fritillary expert. Attendees were shown how to look for the silken webs of caterpillars approaching the end of their winter hibernation. Such webs are often the best way to determine the presence of marsh fritillaries at any given site.

Jane and the other trainees found several larval webs at another nearby reserve managed by the Trust. Last year, 14 adult marsh fritillaries were sighted there. But the team had to survey a lot of devil’s-bit scabious in order to find just 7-8 webs: “It’s a big reserve, around 40 acres, and that’s all we found,” says Jane. “You see all these beautiful larval foodplants, with absolutely nothing on them. And you think: why haven’t the females laid here? They choose their spots very carefully.” I look it up later, and it seems the females tend to lay on larger plants in warm, sheltered spots. Terrain such as earth banks, hedgerows, scrub patches, and slopes are attractive to them, especially if they are in sunny positions. South or east facing slopes are particularly important, and the presence of tussocks is also beneficial, as these create heat traps where developing caterpillars will be sheltered and warm.

After the training day, Jane and the other attendees were each assigned a survey patch. The idea is for the Trust to grow an army of volunteers, who can feed intel back to them. “I can only have eyes and ears in one place at a time,” Ellie concedes. “Having more people looking out for marsh fritillaries is going to be the best hope of knowing what’s happening out there.”

If the Trust succeeds in bringing marsh fritillaries back at Upper Minety Meadows, the next phase will be to connect suitable habitats. Research on the population dynamics of the marsh fritillary has shown that they live in metapopulations. In other words, they rely on a network of colonies that are connected together. “It’s not enough to have one discrete colony,” explains Ellie. “If you had a catastrophe at that site, it would wipe out the population and then it’s never going to come back, at least not for a long time. What you need is a number of suitable sites, close enough to allow for dispersal. That way, the extinction of one local population can be balanced by re-colonisation from another. It’s a case of hedging your bets.”

Just a couple of days after I meet Ellie, she hosts another workshop, this time for local farmers and other landowners. “If they’ve got even a small piece of a field that they could set aside, we’d love to get them onboard. It’s about trying to create a few more little colonies or islands of suitable habitat within the landscape. We’re only one landowner. We need other people to buy into the idea of helping marsh fritillaries.”

It starts to rain, a light drizzle sucked down by the thirsty earth. That’s good news for the devil’s-bit seedlings. There’s now about 760 of them in the soil, where this morning there were none. Not bad for a day’s work. But I wonder how many of them will take hold. “I think if 150 made it, that would be pretty good,” suggests Ellie. “They’re perennials, so they need to develop a good root structure. It could take years before they even flower, but it’s the leaves the caterpillars want anyway.” Of course, in the long-term, the plants will need to flower and set seed so that they can spread naturally through the site. But for now, Ellie and her volunteers will have to keep planting. “Emmett Hill, just next door, has quite a lot of devil’s-bit,” she tells me. “We’ll hopefully harvest some more seeds from there this year, so we’ve got a locally appropriate supply. We’ll then pass some of those to volunteers to grow at home. If we could get 10 people to grow 20 plants, we’d have 200 for the future. Hopefully, with fairly minimal resources, we can build up a good stock.”

But bringing back the butterfly’s foodplant is only part of the puzzle. To ensure it thrives here, the site will need ongoing management. Left to its own devices, the grass sward would become too rank and overgrown, shading out the scabious and other wildflowers and replacing them with quick-growing species like hogweed and nettles. The way the Trust plans to avoid that is to bring in grazers.

Sheep or cattle? I ask.

“Sheep are a definite no-no,” Ellie answers. “They’re precision grazers and will feed on devil’s bit and other wildflowers. Cattle are much less selective. We’ll have a native breed which will do well on rough, improved forage.  If we can get the grazing right, then the devil’s-bit will thrive and eventually spread naturally.”

It’s a tricky balancing act, though. Too little grazing, and the build-up of grasses would overcome wildflowers. Too much grazing, and the habitat would likewise become unsuitable. The butterfly’s sweet spot is a patchy mosaic of short and long, tussocky vegetation. That means long periods of lighter grazing over the spring and summer months, helping to promote a varied age and height structure to the vegetation.

Once widespread in the British Isles, the marsh fritillary has diminished to a mere whisper of its former population. And its story is not unique. Although 2020 was hailed as a good year for UK butterflies—the third in a row—experts warn that our view of what is ‘good’ might be changing. Butterfly Conservation’s Associate Director of Recording and Monitoring, Dr Richard Fox, explains: “It is worrying that, even after three good years, population levels of so many butterfly species continue to be down compared to 40 years ago, with just under a third (31%) of butterfly species assessed in the UK showing long-term declines. We need to be wary of shifting baseline syndrome, whereby we forget (or never experienced) the greater biodiversity that occurred in the UK in former decades and therefore lower our expectations and aspirations for conservation.”

What’s needed, then, is a bit of blue-sky thinking. I ask Ellie what she’d like to see at Upper Minety Meadows in ten years from now. She seems momentarily stilled by the question, as if her mind needs a second to travel the bridge of time.

“I’d like to see a nice patchwork of scrubby bushes of different ages scattered throughout the reserve,” she begins. “Really nice sward structure. Taller clumps interspersed with shorter bits. Loads of wildflowers all around.” She pauses for a moment, like she’s forgetting something important. Then it clicks. “And seeing a marsh fritillary, obviously!” she laughs. “But lots of other stuff flying around too, benefitting from a healthy ecosystem.”

I try to picture the scene in my mind’s eye. It’s a hot, June day on the reserve, and the fields are alive with colour; the air throbs with chirping and buzzing and birds slice through the cloudless sky, feeding on insects so numerous they’re like aerial plankton. A female marsh fritillary takes flight, but her body is too swollen and heavy. She soon resorts to crawling around on the vegetation instead. Close to the ground, she finds what she’s looking for: a healthy devil’s bit scabious plant, which took root a decade earlier. It’s perfect, growing in a sunny, sheltered situation near an oak tree. Its leaves are large and well-developed, standing proud of the surrounding vegetation. The female positions herself at the edge of a leaf, and curls her abdomen around to glue neat rows of lemon-yellow eggs to the intricately veined undersurface. The afternoon sun westers, and it takes her a little over two hours to deposit some 300 eggs, in a tightly-packed cluster four or five layers deep. With the entire clutch laid, her body becomes almost weightless. She takes to the air with ease, and flits between the buttercups and other wildflowers, replenishing herself with nectar. She’s already developing her next batch of eggs. Perhaps she’ll lay them tomorrow, or the day after. Between her, and scores of other females in her colony, thousands of eggs will be laid this season. But by the time the caterpillars hatch in three weeks, much of the scabious will remain untouched. It’s spread liberally around the reserve, and as hungry as the caterpillars may be, there’s more than even their voracious appetites could ever hope to extinguish.