The Ilex Hairstreak (Satyrium ilicis) strongly resembles the False Ilex Hairstreak (Satyrium esculi) but the False Ilex Hairstreak is principally an Iberian species (only in Spain and Portugal and sometimes in southern France).
The Ilex Hairstreak also resembles the Sloe Hairstreak (Satyrium acaciae) which like the Ilex Hairstreak also occurs in southern and central Europe.
However, there are some small differences between the Ilex Hairstreak and the Sloe Hairstreak.
The Sloe Hairstreak is usually paler brown and has larger and rounder red spots on the underside of the hind-wing than the Ilex Hairstreak.
The white band of the Ilex Hairstreak is usually better defined and the array of red-orange spots extends around most of the underside of the hind-wing whereas in the Sloe Hairstreak the orange markings are limited to the areas around the tail.

National Park Zuid-Kennemerland, The Netherlands, 4 July 2018