Darwin's Heath (Coenonympha darwiniana)
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2017 photographs highlighted in yellow. Click on any photograph to go to an enlarged picture, or simply scroll down the page.
Darwiniana is a localised species of the Alpes, but said to be not uncommon in its localities. It is difficult to identify with any degree of certainty because of its similarity to the Pearly Heath (C. arcania) and the Alpine Heath (C. gardetta), the variability of all three species, and, just to make a difficult situation impossible, the interbreeding between darwiniana and gardetta in certain locations.
Gardetta is an altitude specialist occurring mostly at altitudes over 1500m, and although I have usually encountered it only in small numbers, occasionally it is common, but always over 2000m. I feel that gardetta is relatively easy to identify, in France at least, because the bold black rings are (usually) all inside the white band. It has the characteristic silver unh submarginal band most apparent in fresh specimens. There is, however, huge scope for confusion between darwiniana and arcania, although an authoritative source states that arcania does not fly above 1700m so any putative darwiniana significantly above that level should be darwiniana.
From what I can glean, these are the key identification points:
1) colouring: darwiniana is more noticeably orange, whereas gardetta is more grey, rather cooler in colouring. Lafranchis' ID book says that darwiniana unh is grey; this does not match with the description given on Matt Rowlings' site or with several of his photographs of this species.
2) unh white band: the darwiniana unf white band is a similar shape to arcania but less dentate in the centre, and narrower especially in the centre, whereas the gardetta white band is of broadly constant width across its entirety.
3) unf margin colouring: the submarginal unf areas is generally the same orange as the ground colour in darwiniana, in gardetta it is grey.
4) unh s6 ocellus: in darwiniana it is inside the band at the internal edge, whereas for gardetta it is toward the outer edge of the band, and in arcania it is generally just outside the band.
5) ocelli colouring: the arcania ocelli outer rings are generally orange, whereas for darwiniana and gardetta they are yellow, often quite faint for gardetta.
6) ocelli size: the ocelli in s2, s3 and s6 are larger in darwiniana and often absent in s1 and s5; there is a step gap between the ocelli in s6 and s5 (if present).
7) unf ocellus: this seems to be variable but usually present in arcania, absent or very small in gardetta and darwiniana. It is not clear to me whether this holds true in all cases.
However... it is known that hybrid populations of darwiniana and gardetta (and sometimes arcania) occur in the region around the Col de Larche on the French/Italian border, extending northwards and into southern Switzerland. These are known as the form philedarwiniana and exhibit characteristics of the hybridising species. It is acknowledged that the relative distributions are not well known and need further study. So no-one really knows. To quote from the taxonomic study "Bad Species" by Henri Descimon & James Mallet "Coenonympha darwiniana may actually be a stabilized hybrid between arcania and gardetta, since it is found at intermediate elevations between the areas where arcania and gardetta occur (Holloway, 1980, Porter et al., 1995; Wiemers, 1998)."
Until 2009, I had seen individuals mainly in the region of hybridisation which bore some of the features of darwiniana but were never 100% convincing. In 2009 I saw it in the north-eastern corner of the Alpes-de-Haute-Provence, a known region for "pure" darwiniana. In 2010 in the same region, I found a sizeable colony of what I am fairly sure are darwiniana, of which 21862/21859 are an example.
a female, showing an unusual amount of the upperside because it is resting in the grass and the sprig in front is holding the wings slightly open. The orange matches the T&L illustration of the darwiniana upperside very well in that the dark upf band is quite wide and the border between the orange and the darker margin is quite diffuse (T&L shows this as being sharply defined for the arcania upperside).
the underside of 21862. This meets the requirements for darwiniana with only two minor reservations: the white band is quite wide but broadly the same width (in arcania it is more pronouncedly wider in the middle), and the s6 ocellus is at the edge of the white band but not within it (as would be expected for arcania). These two elements are probably within the limits of variability for darwiniana.
|30371||?||the unh white band is of particularly consistent width and markedly non-dentate in the centre, both strong pointers to pure darwiniana. The yellow-ringed ocelli are clear and, as the specimen is fresh, this is a natural yellow colour rather than the effects of ageing and wear. Note that the ocelli in s4 and s5 are significantly larger than in 21859.||1900|