A more usual sitting posture for a Holly Blue, with closed wings
The butterfly with its short tongue stretchedTongue length in butterflies is correlated with body length, so it is not surprising Lycaenids, the family to which the Holly Blue belongs, being small butterflies, have short tongues, around 8 mm. Whites and Brimstone and the Nymphalids have longer tongues, around 15 mm. For their length, some moths (such as the Hummingbird Hawkmoth) have very long tongues, 28 mm. The following table from Pollination and Floral Ecology by Pat Willmer illustrates the length differences between some butterflies and moths.