Larvae of Maculinea (Lepidoptera: Lycaenidae) butterflies are obligate parasites of Myrmica (Hymenoptera: Formicidae) ant colonies. Knowledge of the host ant species has been shown to be crucial for the protection of these butterflies. Furthermore, the identification of the local host ant species can unravel the evolution of this type of parasitic interaction. Host-ant specificity may vary between regions; therefore data should be collected over the geographical range of these butterflies. To understand the host ant usage, 1589 Myrmica nests were searched in 33 sites in the Carpathian Basin (30 in Hungary and 3 in Transylvania) between 2000 and 2007; and for some experiments, caterpillars of Maculinea alcon and M. ‘rebeli’ were adopted and cultured by artificial Myrmica colonies. Maculinea teleius was recorded with six Myrmica species. M. rubra and M. scabrinodis were the most frequently used host ants. M. rubra appeared to be more suitable in the western while M. scabrinodis proved to be more important in the eastern sites. M. salina (first record) and M. gallienii were only locally important hosts on a few sites. M. specioides (first record) and M. vandeli were parasitized in only one case. Maculinea nausithous was recorded exclusively with Myrmica rubra in western Hungary but exclusively with M. scabrinodis in Transylvania. Although no parasitized nests by Maculinea arion were found, there were eight Myrmica species (M. lobicornis, M. lonae, M. rubra, M. sabuleti, M. scabrinodis, M. schencki, M. specioides and M. vandeli) known as potential host ants from M. arion sites. Maculinea alcon was recorded with three Myrmica species. M. scabrinodis was the general host. M. salina (first record) and M. vandeli were found only on a few sites where these species were used rather than M. scabrinodis. Maculinea ‘rebeli’ was recorded with five Myrmica species. M. schencki, M. sabuleti and M. scabrinodis were the most important hosts. M. lonae (first record) and M. specioides were also used occasionally.-----A mirmekofília jelensége sok ízeltlábú taxonnál ismert. Ebből a szempontból a boglárkalepkék különösen érdekesek, mert a legtöbb vizsgált faj hernyója hangyákhoz kapcsolódva él; továbbá a fakultatív és az obligát mirmekofília, valamint a mutualizmus és a parazitizmus legkülönfélébb átmeneti formái is előfordulnak náluk. A Maculinea boglárkalepkék talán a legismertebb obligát paraziták. E lepkék hernyói a negyedik lárvális stádiumban elhagyják a tápnövényt, és utána csak egy megfelelő hangyafaj fészkében tudják befejezni a fejlődésüket.