Butterflies

In our latest blog Lineside Conservation Officer, Kerry Fieldhouse, talks about conducting butterfly surveys along the line at the North Yorkshire Moors Railway...

Nothing quite catches the eye like a butterfly. Seemingly fragile with stunning symmetry, colours and patterns, they never fail to evoke a smile. As my eyes seek to follow their flight, I somehow feel lighter in myself, for that brief few seconds, before they vanish out of sight.   

Butterflies of the UK

There are 59 species of butterfly in the UK but as is the way with so many species these days, The State of the UK’s Butterflies 2015 report found that 76% of the UK’s resident and regular migrant butterflies declined in abundance, occurrence or both over the last four decades (Butterflies (butterfly-conservation.org)

Not all the reasons for this alarming decline is understood and it is likely to be a combination of factors but the destruction and deterioration of habitats is still considered the prime cause of long-term decline. The habitat type will define the butterflies that thrive there but once they are there they need the right food plants for the adults and the right egg-laying plants. Each species has a preference for different plants. They also need shelter from fierce weather and predation mixed with open spaces for basking. A butterfly’s habitat is mixed and varied.

Our lineside habitats on the NYMR once again come into their own. Open areas with a mosaic of wildflowers combined with scrub and taller vegetation nearby combine with the basking opportunities afforded by the ballast and access tracks giving us hotspots that are home to specialist butterfly species, some of which are very unusual.

The Survey

Following a Natural England survey in 2017, the Ecology Survey in 2020 and records from the Butterfly Conservation Trust, I undertook to look for some specialist butterfly species on our lineside this spring and summer.

I was not alone. Together with the Countryside Worker Apprentices, new volunteer Matthew Samuel and expert butterfly recorder, Robert Parks, a volunteer with the Butterfly Conservation Trust (BCT), we surveyed four sites between May and August and were delighted with the results.

The Duke

Starting at Kingthorpe (the famous Adder Wall site) I spent a few sunny days in May this year looking for the very rare Duke of Burgundy butterfly. If you remember back then, it was wet and cold and the mornings were frosty. This is likely to have hampered the emerging ‘Dukes’ who rely on the early spring sun and primroses and cowslips as their caterpillar food plant.

We did however manage to spot one (they are no bigger than a mans thumbnail) and I hope there were many more later. Surveys in other parts of the country recorded late individuals and certainly the primulas were out for a while, so there is hope.

The positive news is that Robert (a lead on Duke of Burgundy in the North of England) was very pleased with our habitat work there and our bid to open out the lineside for more primula to emerge. Our habitat work compliments the work of the BCT in the adjacent Duchy of Lancaster woodland copses and clearings and there were certainly other early species around including a bright batch of passing brimstone!  

The Dingy and the Pearl

Next up was a survey in June at Yorfalls Wood crossing just north of Levisham. We were delighted to find a host of pearl-bordered fritillary dancing in the sun and egg-laying on the violets. This butterfly was once very widespread but has declined rapidly in recent decades, and is now highly threatened in England and Wales.

In amongst them were the strident small skippers (their favourite caterpillar food plant being Yorkshire Fog – that lovely grass whose heads give a purple haze in June), orange tip, green hairstreak and small coppers.

And a real treat was the dingy skipper. It really does look a little worse for wear (!) but being in serious decline in England it is so lovely to have it on our lineside. They were making good use of the ample birds-foot-trefoil at that time of year for egg-laying and basking on the ballast.

Heaths by the heath

Two surveys: one in June from Carters House heading north; and one in July from Fen Bog nature reserve heading south - both served up treats. Ten butterfly species were seen in June on our 1-mile walk (it’s a slooooow walk when looking for butterflies!) including pearl-bordered fritillary and dingy skipper and small skipper but also adding small heath to the collection along with the common blues and tortoiseshell.

The small heath is one of those butterflies for whom life has gotten difficult. Many colonies have been lost in recent decades so watching them skit endlessly across the vegetation in the hope one might just sit still to take a good look at it (!), is a real treat.

In July we were delighted to get good views of the dark green fritillary, a big and bright butterfly that grabs your attention, but we seem to have missed the flying season for the large heath. Obviously, the large heath butterfly doesn’t read books…our guide which told us the end of July was still good for viewing was at odds with the local butterfly recorder at Fen Bog nature reserve who had recorded them a few weeks earlier. There is always next year…

What does it mean?

Surveying and recording both the butterflies and their foodplants helps us look to our future management. We must keep these areas open and limit encroaching scrub and bracken, carefully managing and, if we can, extending habitats to increase movement and dispersal of the species. Knowing that they are still here gives us a good head start and the evidence and motivation to seek funding where needed for continued and better habitat management.