Obligate myrmecophilous butterfl y species, such as Maculinea teleius and M. nausithous that hibernate as caterpillar in nests of the ant species Myrmica scabrinodis and M. rubra respectively, have narrowly defi ned habitat requirements. One would expect that these butterfl ies are able to select for sites that meet all their requirements. Both butterfl y species occur in habitats where their initial larval resource, the host plant Sanguisorba offi cinalis , is abundant, while the ant nests are relatively less abundant. With ants in the proximity of a host plant, caterpillars have a chance of being found by their host ant species, while the host plant could become a sink as caterpillars will die when there are no ants close to the host plant. We tested whether females oviposit on host plants in the close proximity of host ants (ant-mediated oviposition) or whether there is random oviposition, using 587 1-m 2 plots in and around a nature reserve in Th e Netherlands where both species were reintroduced. We found that females of both species indeed more often deposit eggs on host plants nearby ants than on host plants without ants. Visits of adult butterfl ies to plots with the host plant but without the host ants only occurred in years with high butterfl y densities. We argue that understanding site selection for oviposition is important for these highly endangered butterfl y species with a specialised life cycle, especially after disturbances or reintroductions.

Context Road infrastructure construction is integral to economic development, but negatively affects biodiversity. To mitigate the negative impacts of Electronic supplementary material The online version of this article (