Peat bogs are listed among the most threatened habitats in central Europe, a situation that is reflected by, for example, the conservational status of stenotopic butterflies. Even so, this group remains relatively little studied and most of the available data are limited to qualitative records. The present study enabled us to gain insight into the butterfly fauna of the two largest peat bogs in the Knyszyn Forest (NE Poland), i.e. Bagno Moskal and the one in the Jesionowe Góry nature reserve. The sites, only ca 10 km apart, are characterized by similar vegetation (mainly the Ledo-Sphagnetum association). The study was carried out in 2013-2015 using the transect method, i.e. regular counts along fixed routes. A total of 37 species, including three tyrphobionts (Colias palaeno, Plebejus optilete and Boloria eunomia) and two tyrphophiles (Callophrys rubi and Boloria euphrosyne), were recorded. The greatest and unexpected differences between the sites were related to the complete absence of P. optilete at Bagno Moskal, the significantly higher abundance of B. eunomia at Jesionowe Góry and the greater abundance of B. euphrosyne at Bagno Moskal. In addition, C. palaeno was observed sporadically and only at Bagno Moskal. There was some heterogeneity in the distribution and density of particular species, however. Ledum palustre was found to be the most important nectar plant, its flowers also being frequently visited by tyrphoneutrals. The present study shows that isolated island-like habitats (e.g. peat bogs) may possess specific features and be subject to specific independent changes. The results provide a good basis for further research into the habitat preferences of tyrphophilous and tyrphobiontic butterflies, which is important in the context of their conservation.