Cf. based on Seifert, B. 1997c. Lasius nitidigaster n. sp. - a new ant of the subgenus Chthonolasius Ruzksy (Hymenoptera: Formicidae). Ann. Zool. (Warsaw) 46: 201-205 (page 202, Also described as new;worker, queen, male described)
Big queens (10 mm) of Chtonolasius. Jet-black colouration. Wide head with thick short scapes. For size comparison next to a queen of Lasius emarginatus see the last slide. In the wild I observed these parasitic queens hunting down workers of Lasius emarginatus, presumably the main host species (abundant) in the area.
Location is obscured until I track down the neighbourhood area where I found these queens in Hvar.