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.
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
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