Of the invertebrate species between 55 and 60% belong to the Mediterranean biome. So far, over 1200 insect species have been described from the reserve. The diurnal butterflies are of particular interest. In 1992 biologist Zdravko Kolev identified five new butterfly species for Bulgaria — eastern greenish black-tip (Euchloe penia), Phalakron blue (Polyommatus andronicus), Grecian anomalous blue (Polyommatus aroaniensis), Higgin's anomalous blue (Agrodiaetus nephohiptamenos) and Dils' grayling (Pseudochazara orestes); of them all except for the eastern greenish black-tip are Balkan endemic species and all other than the Grecian anomalous blue can be observed in Bulgaria only in Slavyanka and Pirin mountains.