Abstract
T he Large Blue Phengaris arion (Linnaeus, 1758) is one of the most studied parasitic organism in Europe. This myrmecophilous butterfly is entirely dependent on the simultaneous presence of a specific host plant and a host ant of the Myrmica Latreille, 1804, genera. Our study aims to better understand the effects of biotic and abiotic factors on the occurrence and habitat selection of Myrmica ants. We studied the habitat selection by ants in 12 meadows previously known to host populations of large blue. Thirty plots of four square meters were sampled in each meadow. We also conducted phytosociological survey and we compiled the management history in each meadow. We found the presence of two Myrmica species potentially hosts of the large blue : M. spinosior Santschi, 1931 and M. specioides Bondroit, 1918. The habitat selection showed that the occurrence of Myrmica increased with herbaceous cover proportion and decreased with the bare ground cover proportion. Despite the thermophilous nature of these two species within the genus Myrmica, these results suggest that a high grass cover rate is needed for the maintenance of favorable conditions for these species’ anthills. Thus, the maintenance of Myrmica depends on these high-vegetated meadows, partially abandoned lands, a transitional vegetation stage that it is challenging to maintain. In a Mediterranean context, we recommend an as late as possible grazing in season with the maintaining of high herbaceous layer in meadows hosting host ants of P. arion. The total removal of the herbaceous layer is to be avoided