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2009 Donegal Painted Lady Migration 2

 

Following the initial major influx of 31 May – 2 June, a further smaller migration was seen in late June, favoured again by strong south-easterly winds.  In Donegal the cold second week of June was followed by above average sunshine and mean temperatures through the rest of June. July was more variable, especially in the final week, which also was rather windy. Rainfall in the period was about average, or even below in some favoured coastal districts in west Donegal. The result was that the massive Painted Lady egg-laying observed in early June produced huge numbers of caterpillars in some districts and very widespread caterpillars on thistles throughout the county. In the districts with large numbers of caterpillars, they were also to be found on nettles. It is unclear if all those on nettles were laid on that plant or had moved on to them when the thistles had been exhausted. The first records of small numbers of fresh PL adults in late July reported in Dunfanaghy (C03), Dactan/Muckros (G67) and Rossnowlagh/Kildoney (G86) represent the beginning of the Irish-born adults. 

Six coastal areas had reports of exceptionally large numbers of eggs/larvae/adults and are:

South Donegal: Carrickfad (G86), Muckros (G67), and St John’s Point (G76);

Northwest-Donegal: Dunfanaghy (C03);

Fanad: Kindrum (C14);

Inishowen: Inch Island (C32).

 

Carrickfad, nr Rossnowlagh is an isolated area of rough cattle pasture to the north of Rossnowlagh Strand and is where on 2 June Joan and Frank Smyth witnessed massive egg-laying by hundreds of PLs. Since then the area has been kept under observation by Frank Smyth. On 15 July I visited the area with Frank Smyth. Much of the central area of creeping thistle had been severely defoliated by the larvae and secondary re-growth was beginning on many thistles. A few larvae were still present on Creeping thistle, also on Spear thistle and at least three on Nettles. Some of these larvae may have been laid since the original laying event. It is assumed that the majority of larvae that survived are still pupae as no fresh adults have yet been seen there. Frank Smyth reports that even as late as 30 July, no adults had appeared at this site, although small numbers of large fresh adults were present at nearby Rossnowlagh and Kildoney.

Muckros is a low headland on the north-side of Donegal Bay and where Danny Gillespie saw major egg-laying on 3 June in rough meadow. I visited the site on 12 June together with Nollaig Gillespie and Ian McCambridge and saw thousands of eggs and at least twenty adult PLs still flying around in the field. On 24 June I saw hundreds of first instar caterpillars on the creeping thistles as well as one adult PL. On 16 July with Danny Gillespie and Ian McCambridge again I visited this field. There were still at least twenty PL caterpillars at various stages mostly on Creeping thistles but also some on adjacent Nettles. In the centre of the observed egg-laying the thistles were severely discoloured and defoliated. Danny Gillespie reported fresh adults in the area during the last week of July.

 

St John’s Point is a long narrow peninsula to the east of McSwyne’s Bay and Killybegs Harbour and is largely limestone pavement. It is low-lying and has a notably positive microclimate, often escaping much of the rain on the nearby mainland. On 2 June Ralph and Liz Sheppard observed PLs at a density of 3-4 within a radius of 10m throughout and estimated about 20,000 in an area of some 100 ha. On 10 June 10 visited the area and in warm sunny conditions there were still thousands of adult PLs scattered through the lower part of the peninsula from the area of the small strand. On 16 July I visited the area with Ian McCambridge and saw major defoliation of the thistles over much of the area. The only PL larvae I noticed were at six of medium size on nettles nr the lighthouse compound wall.

Dunfanaghy, on 9 July Ian McCambridge saw hundreds of large PL caterpillars on thistles near Horn Head Br and St Michaels GAA grounds. This is a sheltered area and there are lots of thistles on waste ground. On 24 July in the same area he saw three fresh PLs, which probably are the start of the Irish-born generation in this district.

Kindrum is an area in north Fanad and Martin Smith of the Co Armagh Wildlife Society visited the district and reported as follows: “at the weekend of 31 May/ 1 June went to Kindrum and throughout the dunes there was the largest invasion of Painted Ladies I have ever seen – in their hundreds; one sheltered dune had a dozen – they were very active and hard to photo” (info supplied by Ian Rippey).

Inch Island on 1 June Boyd Bryce witnessed hundreds of PLs laying on a patch of Creeping thistles in one of his fields.1  On 6 June he brought the group participating in the annual Donegal Butterfly Field Weekend to see the site. Although the weather was unseasonably cold with a strong NE wind there were still dozens of adult PLs in sheltered areas adjacent to the field. Many thousands of PL eggs were to be seen on thistles in an area of about 10 m2. Subsequently George McDermott visited the site and saw many small larvae of which he took some and reared them in a polythene tunnel. On 26 July I spoke with Boyd Bryce, who told me there were still no signs of emerging adult PLs in the area.

Examination in July of thistles in most areas of Donegal showed PL larvae or the remnants of their tents. These included inland and/or mountainous areas such as the Bluestacks (G88), between Meenirroy and Cark Mt (C00) and at Pettigoe (H16), showing that almost all areas of Donegal received at least some PLs. The larvae in the cooler areas were smaller and may not reach adulthood. On 16 July at a site in the Bluestacks two small larvae were seen by me to be parasitised.  In hot conditions such as in North Africa or in warm artificial conditions the PL can get through a full cycle from egg to adult in as little as a month. Provided the Irish weather is warm or dry the larval stages can survive here, although if it is cold and wet they are likely to die from hypothermia. As the June and July weather in 2009 in much of Donegal has been warmer than average and with above average sunshine the chances of survival through to adulthood are good. Since the length of the larval stages of the PL are mainly temperature controlled, if similar temperatures continue there should be a major emergence in Donegal in the first half of August, at least in the warmer coastal districts.

A surprise has been the large numbers of big Red Admiral larvae seen in July in many parts of Donegal. Although only a few RA migrants were reported in Donegal in early June, clearly they were widespread and have bred successfully. The native RAs should be plentiful in Donegal during the second half of August. The RA is more durable than the PL but tends to be slower in development.

 

Bob Aldwell

31/07/09

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