Into the Mountains (part 2): a scarce mountain moth

 

Black Mountain Moth - Beinn a'Chlaidheimh 22.6.24

(Post updated 10 July 2024)

As mentioned in the last blog post (link here), I like to get out into the mountains. Seeing the wildlife of the uplands is an added bonus. In Scotland, that means frequent sightings of Red Deer, Ptarmigan and Mountain Hares, as well as rarer glimpses of Dotterel and Snow Buntings. I have also been lucky to have a couple of encounters with a moth that rarely descends from the higher peaks. To see one, you need to get your boots on.

I'll start by correcting a possible misunderstanding. You will not find a Black Mountain Moth Glacies coracina (previously Psodos coracina) in the Black Mountains of the Welsh-English borderlands. It is, instead, a black moth that lives on mountains. In fact, its distribution is very limited - within the UK, Black Mountain Moths are restricted to the Scottish Highlands (see NBN distribution map here), usually over 600 metres in altitude. The distribution map shows clusters in two main areas of the Highlands - the Cairngorms (in the east) and the hills around Loch Cluanie and Loch Shiel (in the west). However, I have walked both of these areas on many occasions without seeing one. Both of my Black Mountain Moth encounters were further north, in the Fisherfield wilderness to the south east of Ullapool. I found my first one on the rocky shoulder in the foreground of the picture below; this is Mullach Coire Mhic Fhearchair, which Munro baggers will know as one of the 'Fisherfield Five'. It is awkward to get to: our expedition involved an overnight camp in the glen below. The mountains in the background are the more familiar Torridon peaks, with Slioch the most prominent. 

View north from Mullach Coire Mhic Fhearchair - Black Mountain Moth habitat

The second encounter, last month (June 2024), was on another Fisherfield mountain (Beinn a'Chlaidheimh), when my hillwalking colleague Richard spotted the individual pictured at the start of this blog as we were descedning from the summit. It is highly likely that the relative absence of Black Mountain Moth records in the Fisherfield area is a result of the relative absence of moth recorders on these remote mountains! Needless to say, I have submitted both of my records to the relevant County Moth Recorder, so hopefully a couple more dots will be added to the map in due course.

The first moth that I found (below), one of two that I saw on that walk, was flying low above the ground. This must be a behavioural adaptation to the windy conditions of their preferred habitat. The females tend to stay on the ground, although they are not wingless like some other species. I have only seen males; their flight action makes them more conspicuous. Not a lot else is moving around at that altitude.

My first Black Mountain Moth - Mullach Choir Mhic Fhearchair 19.6.21

Black Mountain Moths have a number of other adaptations to life in the uplands. Their black colouration comes from the pigment melanin which helps to absorb heat more efficiently as well as protect from UV radiation - 'thermal melanism' (Majerus, 2002; Lees & Zilli, 2019). Their furry bodies provide extra insulation. The black colour is also likely to provide some camouflage for these day fliers when seen against the generally dark backgrounds of the peaty and rocky mountain habitats.

A further possible adaptation is discussed in E.B.Ford's classic New Naturalist Moths (Ford, 1955), which states that Black Mountain Moths are more common in odd years of the calendar, with the Northern Dart - an upland moth that I have yet to track down - being more easily found in the even years. He comments that while it is understandable that a high mountain moth might take longer to develop and emerge, the establishment of a two year cycle remains 'mysterious'. Waring & Townsend (2017) say that the two year cycle is 'almost certain' because 'on some sites the adults appear to be more numerous every other year, generally in odd-numbered years'. However, a quick literature search has found no recent work that sheds light on this matter. Indeed, one rather obscure paper (Kaaber, 1996) states that Black Mountain Moth shows no alternate year rhythm in northern Scandinavia. So I wonder how robust this observation really is: for what its worth, my own small sample of records were in both odd and even years. It would be interesting to examine the data in more detail.

Beinn a'Chlaidheimh North Ridge - site of the June 2024 Black Mountain Moth encounter

The global distribution of  Black Mountain Moth emphasises its preference for upland habitats (link to GBIF distribution map here): it is found primarily in Scandinavia, the Alps and the Pyrenees, so its UK population is a bit of an outlier. There is some evidence that, like birds such as the Ptarmigan, it is found at lower altitudes at higher latitudes.

The restricted distribution of Black Mountain Moths - particularly in Scotland - suggests that the species may become a conservation concern in the light of a warming climate. If so, this hasn't been recognised by its inclusion as a UK Biodiversity Action Plan species - although that list is now looking rather dated. (The rarer Netted Mountain Moth is identified as a BAP priority species.) But, short of general climate change policies, its difficult to know what specific actions could be undertaken in respect of the Black Mountain Moth. Its habitats are generally well away from the pressures of development or intensive agriculture. Passing hillwakers generate limited disturbance. The main larval foodplant (Crowberry Empetrum nigrum) has a wider range within the Scottish Highlands than the moth, implying that foodplant availability is not the limiting factor for the moth's distribution.

At the moment, no population trends are available for Black Mountain Moth; the excellent Atlas of Britain and Ireland's Larger Moths notes that there has been a dramatic increase in records over the ten years to 2019, partly as a result of hillwalkers with mobile phones. This suggests greater recording effort rather than an expanding population, but at least numbers of the moth appear to be presently secure. Nevertheless, this species is one to watch carefully in the future.

Acknowledgements

Thanks to Richard Leslie for locating the second Black Mountain Moth on Beinn a'Chlaidheimh and to Phil Sterling for a useful discussion about the species.

References

Ford, E.B. (1955) Moths. London: Collins New Naturalist.

Lees, D.C. & Zilli, A. (2019) Moths. London: Natural History Museum.

Kaaber, S. (1996) 'Notes on Xestia alpicola ssp. atlantica nov.( Lep., Noctuidae) on the Faroe Islands.' Fróðskaparrit-Faroese Scientific Journal, pp.107-113.

Majerus, M. (2002) Moths. London: Collins New Naturalist.

Randle, Z., Evans-Hill, L. et al. (2019) Atlas of Britain and Ireland's Larger Moths. Newbury: Pisces Publications

Waring, P., Townsend, M & Lewington R. (2017) Field Guide to the Moths of Britain and Ireland (3rd ed.) London: Bloomsbury.

 

Into the Mountains (part 1): a bit of botany

 

I've been climbing mountains, mostly in the UK, for much of my life - although moving to Dorset on the south coast of England means that I get out far less often than I would like. The last couple of months have seen trips to the Lake District and the Scottish Highlands respectively. (The photo above is of magnificent An Teallach, near Ullapool in north west Scotland. I'll get to that shortly.)

I'm always on the look-out for interesting wildlife on these walks, although the photographic record is limited to the scope of my iPhone: the SLR and long lens do not accompany me on these expeditions, as its hard enough work already without the extra weight. Mountain plants are of particular interest: if nothing else, they give me an excuse to stop and draw breath.

Anyway, the first trip was a family holiday the Lake District in May 2024.  A showery day saw us climb a couple of fells near Haweswater, including Harter Fell (below). 

View from Harter Fell down to Small Water

The Lake District fells rarely seem as flower-rich as other corners of the British uplands, and the Lakeland fells certainly do not rate as highly as plant rarity 'hotspots' like Teesdale in the Pennines or Ben Lawers in the Southern Highlands. But I was pleasantly surprised by the range of species that we encountered on and around Harter Fell. The track up to Small Water passed a good number of Common Butterworts Pinguicula vulgaris (below).

Common Butterworts - Small Water, Cumbria

Common Butterwort (detail)

While, as their name suggests, there's nothing rare about Common Butterworts, I remain fascinated by carnivorous - in this case, insectivorous - plants. Butterworts have the ability to make their own food: their green colour shows that they photosynthesise. But the pallid yellow-green star of leaves holds a nasty secret: they secrete a stricky mucous-like fluid that captures insects that are slowly digested as the leaves curl around over them. This is a necessary nutritional supplement given the plants' habitat: nutrient poor, often acidic, bogs.

The butterworts weren't alone: another common upland plant carnivore was also present - Round-leaved Sundew Drosera rotundifolia (below - although this image was taken in Dorset a week later). There is something magnificently alien about this species; although of a different family to the butterworts, it 'hunts' in a similar manner. In this case the sticky fluid is more obvious, appearing as small droplets mounted on short stalks. We'll meet another sundew species later on in the blog. 

Round-leaved Sundew

At Small Water, where I had the pleasure of swimming a year before, we left the path and headed south -east following a direct line up the grassy flank of Harter Fell. I wouldn't recommend this as an ascent route, as it gets steep and slippery higher up, but it did take us past some plant-rich wet flushes. The most noticeable flower was one of my favourites: Starry Saxifrage Micranthes stellaris (below).

Starry Saxifrage - Harter Fell, Cumbria

This species (along with Alpine Saxifrage) has now been split from most other saxifrages (Stace, 2019) - it is in genus Micranthes rather than Saxifraga - although this is due to molecular, rather than visual differences. Either way, it's a lovely flower; note the two obvious yellow spots at the base of each white petal. Starry Saxifrage is a widespread species of the uplands (see its NBN distribution map here), and particularly favours wet locations. Well, it's in the Lake District after all.

Nearby was Pyrenean Scurvygrass Cochlearia pyrenaica (below), which is similar to more lowland scurvygrass species such as Common and Danish, which can be found in coastal salt-marshes and inland road verges.

Pyrenean Scurvygrass - Harter Fell, Cumbria

The other notable flowers here were Mossy Saxifrage Saxifraga hypnoides. However, we saw much larger carpets of this on a walk along nearby Longsleddale a couple of days later (below) - a beautiful sight.

Mossy Saxifrage - Longsleddale, Cumbia

Mossy Saxifrage forms mats of often densely-packed white flowers; its linear-shaped leaves certainly make you think of a moss. It is probably the most common of Britain's upland saxifrage species.

The last one from the Lakes trip is a surprise: my first wild Cranberry Vaccinium oxycoccos (below).

Cranberry - Great Howe, Longsleddale, Cumbria

The surprise is that this is the first one that I've ever seen - or at least that I have taken note of. We discovered it on the slope of Great Howe in Longsleddale, which is the route up onto the boggy tops of Grey Crag and Tarn Crag - a couple of outlying Wainwrights. Cranberry is widely distributed across the British uplands (NBN distribution map here), so I'm baffled as to how I have previously missed it. The image above shows a flower, seen from above, and (bottom right) a fruit. The lobes of the flower (corolla) are bent back on themselves ("strongly reflexed"). Cranberry is in the same genus as the more familiar Bilberry (Blaeberry in Scotland) and Cowberry.

A more adventurous expedition into Scotland's Fisherfield wilderness last month added two additional upland flowers to the above tally. Fisherfield is not far from Ullapool in the north-west Highlands and contains some of Britain's most remote mountains; climbing them usually requires a long walk-in followed by a wild camp, as there are no facilities bar a couple of bothies of varying quality. I was last here in 2022 to climb my final Munro (A'Mhaighdean); this time the goal was a (slightly) smaller mountain - Beinn a'Chlaidheimh - which, although previously on the Munro list, was unceremoniously demoted when a resurvey measured it below the magical 3,000 foot height. But it's still a fantastic hill:

View from the summit ridge of Beinn a'Chlaidheimh

We camped in the nearby glen (Strath na Sealga) and approached the mountain from the east. This approach, like many in Fisherfield, is trackless, and we were soon yomping across the usual mix of rock and bog. In one boggy corner, my eyes were drawn to an unusual sundew - Oblong-leaved Sundew Drosera intermedia (below).

Oblong-leaved Sundew - Beinn a'Chlaidheimh

Comparison with its commoner round-leaved cousin (see earlier in this blog) reveals the difference in leaf shape. It is also somewhat redder, although the photos don't really show this well. Oblong-leaved Sundew is most frequent in the north west Highlands - especially north of the Great Glen - but is also found in England and Wales, where it is rarer than Round-leaved Sundew.  There is a third British sundew species - Great Sundew D. anglica - which has similarly oblong-shaped leaves, but is noticeably bigger, with a taller flower-stem (peduncle). 

Further up the hill, I was pleased to see several clumps of Dwarf Cornel Cornus suecica (below).

Dwarf Cornel - Beinn a'Chlaidheimh

These had a distinctly pink tinge, which is unusual; the flowers are usually plain white. Improbably, this is in the same genus as Dogwood, a common hedgerow shrub of the British lowlands. The size of plant and the type of habitat could not be more different. But a closer look at the leaves of Dwarf Cornel reveals distinctly Dogwood-like characteristics - opposite, with lateral veins.

That's it for this brief survey of upland flowers. None of them are particularly rare, but all are worth a more detailed look and they add much to the joy of walking on the mountains and fells.

References

Pardoe, H. (1995) Mountain Plants of the British Isles. Cardiff: National Museums of Wales.

Raven, J. & Walters, M (1956) Mountain Flowers. London: Collins New Naturalist - an oldie, but a classic!

Stace, C. (2019) New Flora of the British Isles (4th edition). Suffolk: C&M Floristics