The Chalkhill Blue (Lysandra coridon) is a small butterfly endemic to Europe (however not in Scandinavia and the Netherlands).
The sexes of the Chalkhill Blue are strongly dimorphic; the males being pale sky blue, and the females being chocolate brown. 
Both male and female have chequered fringes around their wings.
The Chalkhill Blue has a preference for dry calcareous grasslands.

This species was previously known as Lysandra coridon. 
In 2010 it was reclassified as Polyommatus coridon and in 2017 it was again reclassified back to Lysandra coridon.

A mating pair. Fondry des Chiens, Viroin Hermeton Nature Park, Namur, Belgium 12 August 2024