A blizzard of butterflies – “an incredible day” counting northern brown argus

The northern brown argus, at this time of year, is in its twilight months as a hungry caterpillar. The larvae will begin to pupate in May and emerge as butterflies to brighten up small patches of the Scottish countryside through the summer months. Our blog today comes from a mystery volunteer with Butterfly Conservation, who shares with us one of the best days of their own butterfly life…

I have been surveying the transect at Kincraig Point, a rocky outcrop on the north side of the Firth of Forth, since 2013. It follows the Fife Coastal Path from the wooden steps at the beach, on up the steep hill to the top of the cliff and along to the abandoned concrete hut beyond the wireless mast.

Amongst the many varieties of wildflowers found here, there is extensive rock-rose, the larval plant of the northern brown argus butterfly. There were two dreadful fires, in 2013 and 2014, which at the time I thought threatened the very existence of the butterfly in this specialised habitat, but happily, it has survived and gone from strength to strength.

Rock-rose. ©Lorne Gill/NatureScot

We live a couple of miles inland and, once travel restrictions were eased at the end of May, the site became the main focus of my butterfly summer of 2020. On my first post-lockdown visit (29 May), the day I went to put up the butterfly information signs, I counted 31 small heath butterflies along the transect. Despite the indifferent weather, I visited Kincraig as often as possible during the peak flight period, which lasted from 20 June to 20 August. I recorded 284 northern brown argus along the transect route during that time.

My abiding memory of the season comes from two amazing days, one being ‘Super Saturday’ the 20th of June, when in a glory of renewal I saw northern brown argus in five out of six of the transect sections, all freshly emerged and flying with the beauty of new life. Right at the start of the walk, I saw two northern brown argus settled about a metre apart, then one (the male) flew up and fluttered over the female and within seconds they had paired up, flown across the path and mated.

northern brown argus mating pair, 20 June 2020.

I almost gave up the transect at that point, thinking, ‘that’s enough for me’, but I decided to carry on and everywhere I looked I saw the butterfly in all its glory. The day count of 45 included another mating pair at the side of the coastal path, down towards the foot of the cliff.

Could this ever be bettered?! Yes! The following Wednesday 24 June, after three days of cloud and rain, I visited Kincraig again and witnessed a mass emergence! I had never imagined that the phrase a ‘blizzard of moths’ could have been applied to this wariest and most evasive of butterflies, but there they were flying in such unimaginable abundance. It was hot and still, with hardly a breath of wind, low tide and only a few other walkers about. It was the most incredible day, probably one of the best of my entire butterfly life. I counted 103 adults along the transect, plus another 15 in the square beyond the end of section 6 (NT 465997).

Freshly emerged northern brown argus.

Later in the year on 24 July, I watched a female northern brown argus quietly and unobtrusively laying an egg on rock-rose. One of the egg-hunting challenges at Kincraig is that there is so much rock-rose, but I eventually found eggs in Sections 1, 2 and 4.

I also looked more closely at potential sites close to the coastal path. On windy days I found the butterfly sheltering along the field edges on the landward side of where the coastal path runs along the top of the cliff. The ‘square’ beyond the end of the transect heading towards Shell Bay (NT 465997) is, I now realise, the core of the ‘west colony’. I recorded 59 northern brown argus there between 20 June and 24 July.

During my first visits, the Elie Holiday Park at Shell Bay was still closed to visitors. It was an eerie sensation and brought home the full effects of the lockdown, but it opened again in July. The coastal path itself was relatively quiet in late May and June, and throughout the season it was mainly day visitors and walkers, with a few coasteering groups seen in July and August. The discussions I had with Fife Coast and Countryside in late 2019 resulted in a local agreement to reduce path-side strimming in the areas where rock-rose grows, and this proved successful this year. Optimistically, this will increase the areas available for the butterfly to lay its eggs. The final flourish was on 20 August when I saw (and photographed) a northern brown argus, which obligingly flew past at head height and then settled in front of me; ten minutes later I saw the first wall butterfly I have recorded at Kincraig.

Northern brown argus (L) and wall butterfly (R) at Kincraig, 20 August, 2020.

WeekDateSection 1Section 2Section 3Section 4Section 5Section 6Total
1220 June151673445
1324 June212736136103
142 July613143137
159 July815162243
1621 July2115220
1724 July474318
181 August11 2
196 August3231110
2012 August 235
2120 August 1 1
Total 6095882714284
Weekly Transect Count at Kincraig, Fife 2020.
YearSection 1Section 2Section 3Section 4Section 5Section 6Total
Year totals for Transect at Kincraig, Fife.

Although the colony of northern brown argus at Kincraig is the largest known in Fife, there are historical records from other locations. Some of these were visited in 2019 and the presence of the butterfly in Kinghorn, Pettycur and Burntisland was confirmed, after many years without records.

In 2020 the butterfly was found at Monks Cave, near Aberdour, the first record for this location. The historical records have been mapped out, together with records of former known sites of rock-rose, and local members are invited to explore these areas further to see whether the butterfly and/or rock-rose are still there. For further details contact: Fifebutterflies@outlook.com.

For more on Scotland’s butterflies and moths visit www.nature.scot

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