A very small and very rare Pyrgus with very few locations in France, limited to the départements of Hautes-Alpes and Alpes-de-Haute-Provence. Its range extends eastwards through Switzerland and into Austria.

The upperside is characterized by very small white marks on the upf and an almost unmarked uph. However, very small individuals of Large Grizzled Skipper (Pyrgus alveus) and Olive Skipper (Pyrgus serratulae) can occur and both have lightly marked upf. A sight of the underside is probably necessary for confident identification of warrenensis. I have only ever seen this one individual but was fortunate enough to see both surfaces; the underside matches T&L very closely for warrenensis and there very good reasons why it is not serratulae and almost equally convincing reasons why it is not alveus.

There are many more examples on Matt Rowling's excellent web site:  http://www.eurobutterflies.com/species_pages/warrenensis.htm showing the range of markings.

It flies at very high altitudes, Lafranchis giving the range as 1700-2300, although the one individual I have seen was at 2550m. It tends to emerge rather earlier than other high altitude Pyrgus, so this may explain why the one individual I saw looked rather worn on 15 July.

observations

the underside, not a great photo and showing signs of wear but the markings are quite clear enough to confirm warrenensis. This is the underside of 27348.