Alcon is very closely related to the Mountain Alcon Blue (P. alcon (rebeli)). Until recently rebeli was classified as a separate species although, in the past, older reference books recorded rebeli as a subspecies of alcon. Rebeli is now considered to the higher altitude subspecies of alcon and no longer a separate species. Hence the existence of separate pages.

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.

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 underside 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 ground colour 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.

observations

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

a female underside, probably the underside of 13479.

a female egg-laying on G. pneumonanthe.

two ova on G. pneumonanthe.