Widespread but local
Care needs to be taken in identification. This species can most easily be confused with its congener the Provençal Short-tailed Blue (Cupido alcetas). The males of the two species can usually be distinguished by the presence in this species, or absense in the Provençal Short-tailed Blue, of a black crescent-shaped discal spot in the centre of the upperside of the forewing (which though present may be faint). The upper-forewing black margin is very narrow in the Provençal Short-tailed Blue, broader in Eastern Short-tailed Blue. In addition the blue colour of the male upper-wings is more dull and dusky in Eastern Short-tailed Blue, brighter blue in the Provençal Short-tailed Blue. Females of the two species are difficult to distinguish. I cannot find a consistent difference in the undersides.
Both species may also be confused with the Short-tailed Blue (Cupido argiades). On the underside hindwing both species often have a little patch of yellow-orange between the single distinct black marginal spot by the short tail and the remnant black chevron internally. However in the Short-tailed Blue there are always at least two distinct orange patches internally of two distinct black marginal black spots. In addition the orange fills the space between the spots and the chevrons of the Short-tailed Blue, but not in either of the other two species.
Both Eastern and Provençal Short-tailed Blues can also easily be mistaken for Small Blue (Cupido minimus) or even the usually slightly larger Osiris Blue (Cupido osiris). However the short-tailed blues always have some indication of a short tail even if it is little more than a kink for a tail, but this can easily be missed if there is no small yellow-orange mark on the underside hindwing near the tail.
Recorded in 11 (0.6%) of the 1900 10km squares of Bulgaria.
Last recorded in June 2019
Recorded date range (Adult): 04 May to 09 August