Addition of the Comma butterfly as a Breeding Irish Species
The following article is written in the style of the Irish Naturalists’ Journal.
Addition of Comma butterfly (Polygonia c-album (L.)) as a breeding Irish species with notes on the larva and its occurrence in Ireland (Lepidoptera: Nymphalidae)
Jesmond Harding1 and Brian Power2
1Pagestown, Maynooth, County Kildare
2Kildavin, County Carlow
The Comma (Polygonia c-album (Linnaeus, 1758) has as its range North Africa, mainland Europe, Turkey, Central Asia, North China, Korea and Japan (Tolman 2009). The British range is currently expanding (Asher, J. et al, 2001). In Britain the butterfly expanded eastwards, then northwards during the 1990’s and by 1999 its northern range extended to the Scottish border. Since 2000 it has colonised Scotland after a 140 year absence (Thomas 2010). Individuals were also recorded in the Isle of Man during the late 1990’s (Asher, Jim et al, 2001). The Comma was first recorded in Ireland in Portaferry, County Down during the millennium butterfly survey carried out between 1995 and 1999 (Asher, J. et al, 2001). The first confirmed report of the Comma in the Republic of Ireland was of two butterflies in the Raven Nature Reserve, County Wexford by Elizabeth Kehoe (O’ Donnell and Wilson 2009). The next reported sighting in County Wexford was made on 19 September 2005 at Churchtown north of Carnsore Point (O’ Donnell and Wilson 2009), this specimen being photographed (O’ Donnell and Wilson 2009). Further sightings were made at the Raven Nature Reserve on 22 July 2007 (a single butterfly) while three individuals were seen on 23 July 2007 and one on 26 March 2008. Later Wexford sightings were at Eden Vale 27 July 2008 (two) and 31 July 2014 (four) and further sightings there during August 2008 (O’ Donnell and Wilson 2009). A single adult was seen at Courtown on 14 August 2008 (O’ Donnell and Wilson 2009). A specimen in good condition was seen and photographed in the Raven Nature Reserve by Jesmond Harding (JH) and Philip Strickland on 28 July 2012 (Butterfly Conservation Ireland website 2012). Commas have also been recorded in County Wicklow; one in Enniskerry by Kieran Finch on 13 August 2013 (Butterfly Conservation Ireland website 2013) and one photographed in Arklow by Peter Behan on 16 October 2013 (Butterfly Conservation Ireland website 2013). Records also exist for Cos Dublin and Waterford (Feileachan 2013).
Although the adult butterfly has been observed regularly since 2005 no record of breeding has been reported before now (Feileachan 2013).The presence of the Comma in spring (Feileachan 2013) (Butterfly Conservation Ireland website 2014) suggested residency but until an immature stage was found breeding could not be verified.
Brian Power (BP) reported his Comma sightings from Kildavin, County Carlow to JH. BP observed the Comma in Cuilaphuca Wood, Kildavin (S893580) for each of the years 2011-2014 and Andrew Power saw the Comma there in 2010 (Unpublished report). BP saw the Comma late in 2013 (Unpublished report) and in the spring of 2014 (Butterfly Conservation Ireland website 2014). BP observed the butterfly on 14 April 2014, 18 April 2014 and 27 April 2014 (Butterfly Conservation Ireland website 2014). A record from Kildavin village was reported to BP by Maura Clarke on 21 April 2014 (Butterfly Conservation Ireland website). BP also reported the abundance in the wood of the Common Nettle (Urtica dioica) which is the main larval food plant of the Comma. JH believed that these regular sightings strongly suggested residency and breeding. Post-winter Comma populations are static (Heath et al 1992) and the individuals found are therefore unlikely to be individuals from Britain. Commas also overwinter in woodland and remain there in spring since this is where mating and oviposition takes place.
Description of Habitat
The entrance to Cuilaphuca Wood from the main road is a narrow track bordered on both sides by trees and shrubs. The track runs downhill for c.300m before opening in a large clearing. The wood contains mature examples of Sessile Oak (Quercus petraea), Common Beech (Fagus sylvatica), Common Alder (Alnus glutinosa), Common Hazel (Corylus avellana), willow which is probably Grey Willow (Salix cinerea), and birch which is probably Silver Birch (Betula pendula) and some unidentified non-native conifers. The ground layer in areas dominated by Sessile Oak and Common Beech is dominated by Bluebell (Hyacinthoides non-scripta) and Wood Rush (Luzula spp). The track is edged in various places with Bramble (Rubus fruticosis agg), sedges (Luzula spp), Bluebell (Hyacinthoides non-scripta), Bush Vetch (Vicia sepium), Lady’s Smock (Cardamine praetensis) and Common Nettle (Urtica dioica). The clearing contains an area of bare, recently disturbed soil with little vegetation and a larger well vegetated area where strong growth has developed on spoil removed from the adjoining golf course. The vegetated area consists mainly of various broad-bladed grasses, Bluebells, Himalayan Balsam (Impatiens glandulifera), Red Campion (Silene dioica) and large vigorous patches of Common Nettle which occur mainly around the edge of the clearing on sloping areas.
On 17 May 2014 at c.12:05 p.m. Alexander Harding (AH), JH and BP entered Cuilaphuca Wood. The weather was warm and sunny during our visit with temperature at 18 C with a light breeze.
The track was walked and all butterflies observed. All the observers had seen adult Commas previously and were experienced at identifying the species.
During April 2014 BP observed Commas in the clearing fluttering around Common Nettle (Urtica dioica) and feeding on the flowers of a willow, probably Grey Willow (Salix cinerea) at the edge of the clearing. The sites selected for breeding in Britain were observed by JH to be tall nettle plants growing in sunny, sheltered situations, typically in woodland, growing close to a tree line, hedge or wall; the ovum micro-site was near the tip of the upper surface of a leaf growing at or close to the top of the plant. The young larva feeds on the underside of a nettle leaf but the final instar feeds on the upper surface (Heath et al 1990) (Thomas and Lewington 2010). First generation Commas lay their eggs during April and May (Heath et al 1990).We expected the larvae as early instar underside feeders and focussed our search on the undersides of the upper leaves of nettles growing in the nettle clumps. Any leaf showing signs of damage was checked by turning the leaf over and inspecting the underside.
An adult Comma was seen and photographed by BP and JH at 12:12 p.m. when it settled on bramble (Rubus fruticosis agg) present along the track. The broad shape of the abdomen (Heath et al 1992) suggested a female. However determining the sex of the Comma is difficult as there is little sexual dimorphism observable. The individual remained settled on a leaf where it basked until it was caught, examined and released. It flew upwards, and settled high in a tall willow (Salix spp).
At 12:40 p.m. JH found a larva on the underside of a nettle leaf, near the base of the leaf. The leaf had feeding damage on the same side of the leaf, near the base and apex. The larva was firmly attached to the leaf which is explained by the use of a silken support (Heath et al 1990). Interestingly, a newly hatched nest of Small Tortoiseshell larvae (Aglais urticae) was located close by. The plant was part of a large clump situated near the top of the east-facing slope. A further brief search of nearby nettles did not result in discovery of more larvae. The search was ended to avoid potentially damaging incursions into the breeding area. Comma larvae are difficult to obtain in any quantity due to their solitary habits and wide dispersal (Porter 2010) and therefore the finding of a large number was not expected. Three fourth-instar larvae measuring 23mm were obtained during a visit to Cuilaphuca Wood on 30 May 2014. These were found close to where the original larva was located.
Notes on the larva
The larva was photographed in situ by JH and BP and removed by JH and placed in a container to rear mainly indoors to enable a close study of the larval development to be made. The larva measured 7mm in length. It was cylindrical in shape. It had prominent branched spines on the dorsal, sub-dorsal and lateral surfaces of the thorax (excepting the prothorax) and abdomen with a pair of backward-pointing branched cream coloured spines on the final abdominal segment. The head was shiny and black with several prominent white setae. The branched spines were alternately cream and black; the anterior and posterior spines were cream. The ground colour of the larva was black but under magnification the dorsal area showed traces of white while the lateral surfaces were tan in colour. The stage found corresponds to the third-instar larva shown on the UK Butterflies website.
The larva showed mobility feeding on the inflorescence and leaves on individual plants. When transferred to adjoining plants it remained close to the top of each plant. At this stage it favoured leaves, both young and more mature leaves situated c.6cm to 16cm from the top of the plant. Feeding from the underside and near the leaf apex was observed. Feeding was followed by long periods of resting, with the motionless larva semi-curled on the underside of the leaf; it was also observed to roost in this attitude. When the larva entered the fourth instar around 18 May 2014 the dorsal surface of the abdomen was now more distinctly white. All the abdominal spines except those on the first segment (A1) were now cream while the spines on the other four segments closest to the head were tan in colour. The first thoracic segment lacked the branched spines. Growth accelerated during the fourth instar. The larva still fed underneath the leaf but consumed larger areas at a faster rate and tended to remove larger areas of the edge more frequently rather than perforating the interior.
A moult was completed on 25 May 2014 when the fifth instar larva measured 18mm. The appearance was as described for the third instar but colours were sharper and markings better defined. The larva still fed on underside of the leaves and maintained its preference for the leaf base and apex; it also now fed on leaves further down the plant. On 27 May 2014 the larva measured 23mm. When disturbed it contorted into an indefinable shape which closely resembles a bird dropping. By 30 May 2014 the larva was fully fed, reaching 33mm then left the foodplant to pupate (Fig.1). Interestingly, the larva observed never fed on the upper side of the leaf despite literature reports (Heath et al 1990) (Thomas and Lewington 2010) stating that it does so during the last instar. The adult Commas that emerged from additional larvae obtained from Cuilaphuca Wood proved to be the golden coloured form known as hutchinsoni. Unlike the darker form of the Comma which delays breeding until spring, form hutchinsoni does not have a reproductive diapause. On 22 July 2014 BP observed oviposition by three Commas taking place along the River Barrow near Borris, County Carlow confirming that the species is double-brooded in the wild in Ireland.
Key questions are how and why the Comma expanded its range to Ireland and its brood structure in Ireland. According to Thomas (2010) the Comma, like the Small Tortoiseshell, lives in loose, open populations and wanders through the landscape in search of food, over-wintering sites and breeding areas. This non-colonial habit suggests that introduction by humans is unlikely to be the cause of its presence since any individuals released are likely to disperse widely without finding a mate. A sustained colonisation is the more likely explanation for its presence. Although not regarded as a true migrant it demonstrated the mobility required to re-occupy Southern England in the early twentieth century following a nineteenth century decline that saw it confined to Gloucestershire, Herefordshire, Monmouth and a few adjoining areas (Thomas 2010). From Southern England it expanded northwards and eastwards throughout most of the twentieth century and the population size increased on sites where the Comma was already well established (Thomas 2010).
The factors driving this expansion are unconfirmed but according to Thomas (2010) a warming climate seems the most plausible although the switch from Hops (Humulus lupulus) to nettles as a foodplant may also be significant (Thomas 2010). This factor and South-east Ireland’s proximity to an expanding British population may explain its presence here; according to Tolman (2009) “short/medium term residency in areas close to (the) limit of (its) range possibly relate to erratic or periodic increases in adjacent, permanent populations accompanied by dispersion”. Throughout Wicklow, East Carlow and Wexford a number of woods contain the larval host plant growing in suitable conditions where searches may reveal many more breeding sites. Records of the species at various places along the River Slaney (Butterfly Conservation Ireland website) suggest that the butterfly may be using the wooded river banks as a corridor to extend its range in the South-east. The challenge in confirming breeding partly lies in locating the larva. This arises from its solitary habit, its ability to conceal itself by remaining under the nettle leaf until and even during the final stage and the older larva’s cryptic appearance during its final stage (Porter 2010).
Another challenge in locating the larva lies in the butterfly’s brood structure. The Comma is partly bivoltine in Britain with the first generation arising from spring eggs with a partial second brood arising from summer breeding by part of the first generation. There is a reproductive diapause in part of the first brood and all of the second brood and these are the butterflies that over-winter and breed in spring (Thomas 2010). Early springs and long daylight favour the production of two broods while late springs and cooler conditions lead to a smaller second brood or a single brood (Thomas 2010). Ireland’s climate often brings considerable cloud cover and therefore in some years a second brood may be small or non-existent, so the best time to seek the larva under such conditions is May and June. A second brood produces larvae in July and August and this is when the summer larvae should be sought. While a second brood occurred in Carlow and Wexford during 2014 (Butterfly Conservation Ireland website 2014) it will be interesting to investigate how the Irish Comma’s brood structure varies according to weather conditions.
We acknowledge Ken Bond’s assistance in editing the manuscript and for his comments and advice and all observers who reported their sightings of the Comma butterfly. Thanks also to Richella Duggan for reviewing the manuscript.
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