Alcon Blue (Phengaris alcon)

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2019 photographs highlighted in yellow. Click on any photograph to go to an enlarged picture, or simply scroll down the page.

13479_female_Vienne_15Aug08 46903_male_Ain_25Jul19 46897_female_Ain_25Jul19
46924_female_Ain_25Jul19 46931_ova_Ain_25Jul19 13564_female_Vienne_15Aug08
 
13505_female_Vienne_15Aug08 13492_ova_Vienne_15Aug08  

Alcon is very closely related to the Mountain Alcon Blue (P. alcon (rebeli)). It was only recently that rebeli was considered to be a separate species and older reference books record rebeli as a subspecies of alcon. They are very similar in size and colouring and the undersides are almost indistinguishable, although the altitude is the best differentiator - if it's at high altitude, it's almost certainly rebeli. In the recent re-classification of scientific names rebeli is now considered to the higher altitude subspecies of alcon and no longer a separate species.

Both rebeli and alcon are reportedly quite rare and their habitat is threatened, especially alcon. I have, however, seen rebeli in a number of places, only ever in small numbers, so maybe I've just been lucky. Up to 2019 I had only seen alcon in one place which I was taken to in 2008, and would never have chanced upon the location (thanks are due to Neil Wilding). The females were constantly egg-laying on Marsh Gentian (Gentiana pneumonanthe), so were easy to photograph, whereas the males were whizzing around, never settling, chasing after females that generally weren't interested. In 2019 we did chance upon a small colony in eastern France and it took a few moments to realise that it was alcon that we were looking at, mainly because it was not clear what plant the female was egg-laying on (see note below on 46931).

 

This species was previously known as Maculinea alcon.

ref sex

observations

alt. m
13479 F

a female, with almost no blue scales, and with a clearly visible upf discoidal spot and a faint post-discal mark in s2.

100
46903 M a male, late in the flight period and showing some slight signs of wear. 700
46897 F a very fresh and appealing female, heavily gravid, and taking a rest in the shade after a hectic spell of ovipositing, some of the results of which can be seen in the image for 46931. 700
46924 F the same female as 46987 in the act of ovipositing. 700
46931 OVA a batch of eggs in the area where the flowerheads of the Marsh Gentian would develop. Curiously, the Marsh Gentian were not even close to being in flower at this location. From what I understand of the period in which the Gentian is in flower, it is usually late summer but it still seems unusual that there not even any flower buds on 25 July. 700
13564 F

a female underside, probably the underside of 13479.

100
13505 F

a female egg-laying on G. pneumonanthe.

100
13492 ovum

two ova on G. pneumonanthe.

100

 

13479_female_Vienne_15Aug08

 

 

46903_male_Ain_25Jul19

 

46897_female_Ain_25Jul19

 

46924_female_Ain_25Jul19

 

46931_ova_Ain_25Jul19

 

13564_female_Vienne_15Aug08

 

13505_female_Vienne_15Aug08

 

13492_ova_Vienne_15Aug08