Chalkhill Blue

Polyommatus (Lysandra) coridon

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Ppolyommatus coridon

Male, Switzerland, August 2014

Polyommatus coridon

Male, Switzerland, September 2016



Male, Switzerland, September 2012



Male, Switzerland, August 2012

Polyommatus coridon

Mating pair, Spain, July 2017

Polyommatus coridon

Mating pair, Switzerland, August 2013

Polyommatus coridon

Mating pair, Switzerland, October 2013

POlyommatus coridon

Female, Switzerand, November 2015

Polyommatus coridon

Male, Switzerland, July 2013

Polyommatus coridon

Female, Switzerland, July 2013

Polyommatus coridon

Males, Switzerland, August 2013 (I'm not 100% sure what the butterfly in the foreground is)

Polyommatus coridon

Male, possible hybrid with Spanish chalkhill blue, Aragón, July 2017 - or a very blue Spanish chalkhill blue

Polyommatus coridon

Male, possible hybrid with Spanish chalkhill blue, Aragón, July 2017 - or a very blue Spanish chalkhill blue

Polyommatus coridon/albicans

Underside of one of the above two butterflies, looking very like Spanish chalkhill blue



Female, Switzerland, August 2012



Female, Switzerland, August 2012



Female, Switzerland, August 2012

Val d'Aran, July 2005



Male, Switzerland, July 2011



Male, with Adonis blue and Piedmont ringlets in the Pyrenees, July 2011

Two (rather different) males, Val d'Aran, July 2005



Male, Switzerland, July 2009



Male, Switzerland, July 2008

Polyommatus coridon distribution

Distribution

The chalkhill blue is a common butterfly of chalk grassland, from lowlands right up to high in the mountains, in most of central and southern Europe, reaching as far north as southern Britain but absent from the southern half of Iberia. It is one of a complex of closely related species and subspecies that can be tricky to identify where they overlap and hybridise. This is particularly true in northern Spain.

The male is a rather pale, silvery blue above - but very clearly blue, rather than blue-white, as in Spanish chalkhill blue. The dark borders are typically thick but this is very variable. In some individuals it comprises little more than a row of dark, somewhat conflated submarginal marks. In others, there is a further dark line inside this, giving the impression of a double marginal band, and in still others the submarginal markings and the line inside are conflated into a single, thick band. There are always submarginal spots inside the outer margin of the hindwing. The fringes are chequered - most strongly on the outer half of the fringe - and there is a cell spot on the underside forewing. Similar species include the Provence chalkhill blue, the Spanish chalkhill blue and what Leraut calls the Albarracin chalkhill blue, Polyommatus caelestissimus. The first of these is double-brooded and so easy to identify in its first brood, when chalkhill blues do not fly. In its second brood differentiation is more subtle. I am not familiar enough with Provence chalkhill blues to be sure I can tell them apart with certainty, mainly because of the huge variability of chalkhill blues. Spanish chalkhill blues are almost pure white in the south of Spain, where chalkhill blues do not fly, but a very delicate blue in the north. I illustrate a couple of males above in a region of overlap which closely resemble Spanish chalkhill blues except that they are much bluer. I have yet to see caelestissimus. This species is a brighter blue. Female chalkhill blues are even harder to tell apart. She can be confused not just with the other chalkhill blues but also with adonis blue. However, she rarely has as much blue on the upperside as that species and in particular, the pale crescents inside the orange submarginal lunules are whitish, without blue scales.

Chalkhill blue caterpillars feed on horseshoe vetch. In much of Europe the species hibernates as an egg, but in Greece it is said to hibernate as a second-instar larva (Tolman). Like most blues, the chalkhill blue has a close relationship with various ant species.