Abstract: Field data on ant associates of 98 species of Palaearctic Lycaenidae butterfly immatures were collated. Members of 21 ant genera from the three subfamilies Myrmicinae, Formicinae, and Dolichoderinae have been reported as ant attendants with certainty. All ants that visit lycaenid immatures also forage for other liquid carbohydrate food sources like extrafloral plant nectar or homopteran honeydew. Species of Lasius (recorded with 41 lycaenid species), Formica (24 spp.), Camponotus (24 spp; all Formicinae), Myrmica (25 spp.), and Crematogaster (26 spp.; both Myrmicinae) are the most important ant associates of Palaearctic lycaenids. Available data have almost doubled relative to the last synopsis 15 years ago, but general patterns remained robust. The recorded diversity of butterfly-ant associations has slightly increased due to the improved data-base, including the addition of six ant genera previously not reported as tending Palaearctic lycaenids. Ant associations in the Oriental, Australian, and Nearctic faunal regions are more diverse than in the Palaearctic, whereas those in Africa are less diverse. The number of lycaenid species associated with a particular ant genus correlates moderately, but significantly with species richness of that ant genus in the Palaearctic region. Exceptions to that rule can be explained by specific ecological and behavioural traits of the respective ants. Ecological dominance is the most important factor with regard to the involvement of ants in interactions with butterflies. Obligate myrmecophiles are rare among Palaearctic lycaenids and are highly host specific (but usually on the ant genus rather than species level), in contrast to opportunistic visitors in facultative associations. Obligate associations in the Palaearctic region are biased towards the genera Myrmica (hosts of the unique, socially parasitic Phengaris-Maculinea clade) and Crematogaster (hosts of Aphnaeini species).

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