The Comma, Polygonia c-album
The Comma butterfly with its very odd wing shape is an unusual and attractive resident of Hadlow parish, including over-wintering as adults in sheltered places in woodland for example. Like the other Nymphalid “Admirals” (Red Admiral, Peacock, Small Tortoiseshell) it is a bit of a wanderer, not restricted to particular colony sites, and individuals can be found in various places across the Parish.
Commas are generally quite a bright orange when first seen flying, and when examined more closely, the uppersides are a complex pattern of dark blotches on an orange ground, complicated by the outlandish and uniquely “serrated” wing shape. When they close their wings however, with the underside of their front wings hidden by the backwings, they appear completely different, camouflaged in a complex pattern that from a distance appears an overall dark grey.
This is a fairly fresh individual at the start of July 2017, possibly of the brighter Hutchinsonii form, that urgently mates, and quickly lays eggs for a second generation that same year. The relatively un-convoluted wing edge suggests a female.
This individual is showing a little wear on the front edges, rear edges and a few other areas of the wings by the beginning of July, and I am fairly sure that it is still definitely an Hutchinsonii. The bodies of Comma adults are often quite plump:
This photo shows the long hairs on the upper side of the wings close to the abdomen, that might help with trapping warm air. I haven’t seen anything in the literature to support this view though. Alternatively, perhaps they help stop cold rain getting to the abdomen?
This is a picture of the same phenomenon, but showing how I think the abdomen can be fitted into the tunnel of the wings. I imagine that the wings can be parted or closed up according to the thermal needs of the abdomen. This picture was taken on a warm evening in July, so one would expect the wings to be parted as in fact they are in this photograph. The relatively un-convoluted edge of the wing may indicate a female:
This is looking up against the sky, but still of the brighter, quick to mate, Hutchinsonii type with its wings quite outspread. definitely a colourful insect!
In this picture the butterfly still appears quite bright, but there are dark, contrasting patches.
In this individual, no sign of the orange in the wings remains, and the camouflage of a dead leaf, or of bark, becomes almost complete.
This photograph is of an individual potentially about to enter hibernation, as it was taken in October, while the insect was nectaring on the vitally important late-flowering ivy flowers. Notice how much darker it is even than the photograph above. Does the melanin in the wings increase as time goes on? I read nothing in the books about this:
Comma butterflies can be found over most of Hadlow parish in the summer, in woodlands, farmlands and gardens, and can be quite common in July to October in a good year. The over-wintering adults from the second generation (more rarely from the first), tend to be rather more limited in distribution and in the autumn might often be seen in gardens, before they move into woodlands to hibernate.
After hibernation, as they re-emerge in the spring, they are most likely to be found sunning themselves on footpaths through farmland or tracks through woodlands. Good footpaths are those around the Access Trail between Hadlow and Golden Green, the footpaths towards the River Medway and also the footpaths between the College’s Equine Unit and Clearhedges Wood.
Nationally, the Comma went through a terrible numerical and range contraction in the 1800s, becoming confined to a few counties in the Welsh Marches by the turn of the century, becoming nearly extinct in the UK. However it has, amazingly, since the First World War, recovered all the ground lost, and now extends even into southern Scotland, after an absence of 140 years or more. The reasons for its decline, near loss and then remarkable recovery can only be guessed at.
It is currently continuing to expand its range, about 170 km northwards in the last 30 years, which some have linked (perhaps simplistically) to climate change. Few other butterflies have shown this northward shift.
Over-wintering adults mate in March, giving rise to the spring generation of caterpillars on nettles, and the “July” generation of adults. I think the butterflies seen in July are often quite likely to be the brighter “Hutchinsonii” form, which will mate and produce a second summer generation of caterpillars and adults appearing in August. These “August” generation adults are always a bit darker and these are generally the butterflies that are likely to over-winter.
However, in addition some of the later butterflies in the “July” generation will also be darker and “too late” to breed in the summer, and will also over-winter like all the “August” generation, not breeding until the following March. The change to the darker over-wintering form that will breed in the spring is thought to be controlled by the daylength the caterpillars experience – as the daylength decreases the darker over-wintering form of the adults is produced.
Any of the darker “about to over-winter” individuals, whether from the “August” or the “July” generation of adults might well be found in gardens in September and October, feeding up ready for hibernation on flowers or rotting fruit. Any of the brighter individuals from the “July” generation, the “Hutchinsonii” form, will have mated to produce the “August” generation, and died by now.
Traditionally the caterpillar food plant in the UK was agreed to be hops, grown almost everywhere for the brewing of beer for about a thousand years, but with the decline of its cultivation for brewing, nettles or in some areas Wych elms are nowadays known to be the usual foodplant of the Comma in the UK.
Nettles are also used by some populations of the Comma in Europe and may have been used by the UK population in the past in spring before the hop plants entered full growth, and perhaps further back historically before hop plants were widely grown. The single glossy green eggs are laid on the upper surface of tender leaves, sometimes on the extreme tip. Plants chosen may often be on the edge of a wood, scrub or a hedge, almost never in the open countryside. The caterpillars of this species feed individually, rather than in large communal groups.
The later caterpillar stages of the caterpillar – it used to be said – look like a bird’s dropping. It has a splash of white at one end, and orange and black colours at the other, all protected by sharp and tricky to handle spines. As the caterpillars get bigger and moult into their different stages they are less likely to be attacked by invertebrates and more likely to be attacked by vertebrates, particularly birds. When chicks were offered these caterpillars they were put off by the spines, did not eat or even damage most of them, and very effectively learnt to avoid eating similarly coloured larvae again.
This effect was not found when the spines had been carefully removed before offering the larvae to the chicks, indicating that the chicks were only put off the colours of the caterpillars by the unpleasant effect of the spines. This association is called an aposematic effect in biology, and the idea is used in so called “aversion therapy” in humans.
Here is a lovely example of a late Comma caterpillar suspended from a leaf and about to pupate:
The chrysalis, in contrast to the later caterpillar stages, is very heavily camouflaged and is designed to look like a dangling withered leaf.
The dark patches, more enhanced in the over-wfurther back in intering individuals, are created using chemicals such as melanin, using up scarce nitrogen, an element thought to be in short supply in the caterpillar’s diet. The short-lived summer Hutchinsonii form may sacrifice some of its ability to protect itself with melanin by diverting nitrogen into more rapid reproduction in some way, then dying soon afterwards.
Like many other butterflies, an adequate salt supply may be essential for optimum activity and successful reproduction (especially by the female, salts may be involved in nuptial gifts from the male?). Butterflies may therefore be found apparently taking salt from paths, car tyres, or even as in this case, dog’s mess. This individual looks very dark and is therefore likely to be an over-wintering type, while the exaggerated wing scalloping suggests a male!
Predators and parasites
Birds are a major threat. The overwintering generation lasts longer and is therefore darker above than individuals of the short summer generation of bright Hutchinsonii, helping to reduce predation. When the over-wintering butterflies close their wings however, as they will do when actually hibernating, and as seen above, their camouflage of a dead leaf is almost perfect, and the insects can be very difficult to spot indeed!