Alcon Blue (Phengaris alcon)
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2021 photographs highlighted in yellow. Click on any photograph to go to an enlarged picture, or simply scroll down the page.
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.
It appears to me that the colouring seems rather variable, compare 47595 and 47643, for instance. Most females seem to have a rather cinnamon colouring but some are more bluish grey-brown. Of the few males I have seen, the uns seems to be a more silvery grey-blue.
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).
I returned to the same site in 2020 (not in breach of Covid-19 restrictions) and was delighted to find alcon flying there. It did seem that there was only one, maybe two, females and similarly for males. However, on detailed study of the markings I found that there were at least three different females, but only one male. They tend to have bursts of egg-laying on what were clearly more developed G. pneumonanthe (see 47603 for instance) than on the same date in 2019, followed by rest periods, which would explain why only one female was seen at any one time.
This species was previously known as Maculinea alcon.
|47651||F||a rare opportunity to see the upperside, as this female rests in between bouts of egg-laying. It opened up briefly to absorb the warmth of the sun and revealed this beautiful blue smattering of scales in the upf basal region. I believe that 47643 is the underside.||700|
a female, with almost no blue scales, and with a clearly visible upf discoidal spot and a faint post-discal mark in s2.
|47620||M||a male, as clearly indicated by the extent of the blue scales just visible on the upf. It has a steely blue colouring. 47636 is the same butterfly.||700|
|47636||M||a male, the same butterfly as 47620, showing a very slightly different colouring, indicating that the angle of viewing has an effect.||700|
|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|
a female underside, probably the underside of 13479.
a female egg-laying on G. pneumonanthe.
|47595||F||a female, with quite a dark cinnamon colouring. 47603 is the same butterfly.||700|
|47603||F||a female, the same butterfly as 47595, egg-laying on G. pneumonanthe.||700|
|47615||F||another female, very similar in appearance to 47595 but it is in fact not the same butterfly.||700|
|47643||F||a female with an unusually pale greyish-blue colouring. It may only be partially due to the viewing angle. I believe 47561 is the upperside.||700|
|47661||F||another female, rather more-greyish-blue than the norm (assuming 47595 is the norm), but not as pale as 47643.||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|
two ova on G. pneumonanthe.