The first small tortoiseshell I’ve seen this year has just fluttered past – and my heart soared. This is one of those iconic common and widespread butterfly beauties that reminds me of my childhood roaming semi-feral across the South Downs and Sussex Weald in the late 1960s and early 1970s.
With its black-and-yellow spiky caterpillars feeding on stinging nettles in every hedgerow and its habit of sunning itself in the middle of a footpath, it was so familiar to me that I usually passed it by with little more than a glimmer of recognition and acknowledgement. So many sad ironies now rear their ugly heads.
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You don’t see many small tortoiseshells these days, that’s for sure. I’m not just being some sentimental ‘old boy’, as my uncle used to call the gnarled fellows who picked cherries and apples on his North Kent farm – I am genuinely now one of the lucky ones. Many people will not see a single small tortoiseshell this year. According to the latest reports, 2024 was the butterfly’s worst year since records began. And it is not alone. Those records, collected through the UK Butterfly Monitoring Scheme since 1976, have amassed a vast database following the annual ups and downs of the 58 butterfly species generally regarded as being native to the British Isles, and a few irregular migrants. Mostly these have been downs.
Butterflies are fickle; one minute they are flitting about in the sunshine, the next cloudy moment and they are gone, hidden, wings closed, in the undergrowth. But nearly 50 years of regular recording has given British butterflies a powerful status, not just as attractive flagship species, but as real fingers on the environmental pulse. Three thousand butterfly transects – which are fixed routes 1–2km long – are walked by volunteers every week from April to September, with butterfly species and, more importantly, numbers recorded in different segments along the way.
Weather patterns and seasonal changes come and go, but the regularity and reproducibility of these monitoring walks means the data collected is robust and scientifically quantifiable. These hard numbers show a real picture of the natural world and what is happening in it. And they reveal changes over years and decades.
Which butterfly species are declining in the UK?
Some of the first warning signs came when Butterfly Conservation, and the other partner organisations operating the recording scheme, published The Millennium Atlas of Butterflies in Britain and Ireland in 2001. Though many common and garden species (such as the small tortoiseshell) that fed on common and widespread plants seemed to have been doing okay, specialist species that were attached to uncommon food-plants in limited habitats, such as coppice woodland, lowland acid heath, chalk downland, or coastal undercliffs, were fast disappearing.
Never common but always relatively widespread in southern England (I saw it regularly in Ashdown Forest), the high-brown fritillary had gone from over 90% of its former range – a cataclysmic fall. Likewise, the Duke of Burgundy (a regular skipping over the grass tussocks in Vert Wood near Laughton), grayling (clouds of them on our family holidays to the Dorset heaths), wall (prosaically named and often seen resting on its namesake bricks) and many others had gone into precipitous decline.
Regular status updates from Butterfly Conservation continue to monitor the changing fates of our butterflies, but 2024 was a real shocker, leading the charity to declare a ‘butterfly emergency’. As well as the continued drip-drip-drip trickle decline of specialist species over decades, once ‘common’ regulars, such as the green-veined white, small copper and large skipper also had their worst years on record.
Part of 2024’s bad butterfly results can be put down to the weather; a cool spring and a wet summer were never going to favour warmth- and sun-loving butterflies. But that was just the tipping point.
Since the middle of the 20th century, industrialised intensive farming, removal of hedgerows, urban sprawl, pesticide spraying, road-building, changes to woodland and heathland management, and the commercial unviability of downland grazing have drastically altered the British landscape and fragmented butterfly habitats to the point where small isolated remnant colonies barely survive and can not bounce back from poor weather events like they used to. Any resilience in the previously much more joined-up landscape mosaic has been eroded. Similar butterfly losses have also been recently reported from Europe and North America – for the same reasons.
Which butterfly species are thriving in the UK?
It’s not all doom and gloom, though, as there have been some successes. In 1979 the large blue was officially declared extinct in the British Isles, but a dawning understanding of its habitat needs – limestone hillside grazing at just the right level, not a bit more, not a bit less, to favour the ants in whose nests it bred – led to a reintroduction programme using similar genetic stock from Sweden. Britain now has five strong core populations from which natural colonisation to new sites is increasing. A recent Butterfly Conservation estimate suggested 10,000 individuals on nature reserves in Gloucestershire and Somerset, ironically making this country a relative stronghold for the species, with one of the largest concentrations of the butterfly anywhere in the world.
One of Britain’s largest butterflies, the purple emperor, is also increasing and spreading year-on-year. I never saw it as a boy, even though the Weald was one of its supposed heartlands. I’m led to believe that rewilding at the Knepp Estate in Sussex means they start flitting around you in the car park these days. And it has now spread much further north – into East Anglia and the Midlands. When I finally got to see one near Aylesbury in Buckinghamshire a few years ago it took a few moments for me to realise what this strange unfamiliar butterfly was – then I almost burst into song.
Other increases include the Essex skipper (which perhaps ought to be renamed English skipper since it now occurs in almost all of the country), comma and speckled wood, all of which are spreading northwards, right up into Scotland and may be extending their geographic ranges because of climate change and warming weather.
There are some local good news stories too. Bucking the general downward trend of the small blue in Scotland, unusual April warmth brought it out in record numbers this year – 523 of them on a single day at the Balnagown Estate near Invergordon. And wherever conservation work is directed specifically at butterflies they are generally doing well.
The heath fritillary is one of Britain’s rarest butterflies, with the largest populations in the Blean Woods of Kent and on Exmoor, where traditional coppice management by conservationists has saved it from the brink of extinction. Serendipitously, this work to bolster the butterfly’s larval food-plant – cow-wheat – has also improved the lot of the rare cow-wheat shieldbug at these reserves.
But the general butterfly picture is downwards. Though they were never common, grizzled skipper, small pearl-bordered fritillary and chalk hill blue are now teetering over the abyss of ‘threatened’ status on Britain’s butterfly red list. For all of them, 2024 was also their worst year on record. Indeed, 51 of the 58 monitored species did worse in 2024 than in 2023.
How can you encourage butterflies in your garden?
A slightly disheartened Richard Fox, Butterfly Conservation’s head of science, admits: “I’m struggling to think of any positives, but our research on letting grass grow long in gardens, leading to sightings of more and greater variety of butterflies, is quite good news – especially as we found that the benefits of long grass were greater for urban and suburban gardens, which of course is what most people have.” This is, perhaps, tied into the well-publicised ‘no-mow May’ campaign, but is also a reflection of the increasing understanding that a slightly untidy garden will have more wildlife than a manicured plot.
Slightly untidy gardens are also likely to be the viewing platforms of choice for Butterfly Conservation’s Big Butterfly Count. Alongside nearly 50 years of painstaking transect monitoring, the Count complements it in its simplicity. It may seem trivial, just identifying and counting a few butterflies for a random 15-minute period sometime between 18 July and 10 August, but the sheer numbers of people taking part make it the world’s largest butterfly survey; over 85,000 people submitted more than 140,000 counts in 2024.
Although I’ve no idea whether I will see zero, one or 10 species in any 15-minute period, I’ll do my bit too. And I’d like to believe that my small tortoiseshell is in the vanguard of a wildlife influx to a plot right in the centre of urban London.
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Main image: small tortoiseshell butterfly. Credit: Getty
