Eleven blackfly species were collected in the southern part of the Lapland State Biosphere Nature Reserve. Among these, six species, Prosimulium macropyga (Lundstrom, 1911), Boreosimulium annulus (Lundstrom, 1911), Schoenbaneria pusilla (Fries, 1824), Odagmia rotundata Rubzov, 1956, Archesimulium tuberosum (Lundstrom, 1911), and Argentisimulium noelleri (Friederichs, 1920) are common in this region; Archesimulium polare (Rubzov, 1940) is recorded from the Kola Peninsula for the first time; Gnus decimatum (Dorogostajsky et al., 1935) is recorded from the northern part of European Russia for the first time. A new species, Argentisimulium tshuni sp. n., is described from the male, larva, and pupa. The diagnostic characters of the new species are as follows. The male differs from those of the all other species in the presence of a conical projection in the distal part of the gonostylus, absence of an apical spine, presence of one very large spine in the parameres, and shorter gonostylus. In addition, the male differs from most of the congeners in the obsolete basal wrinkled part of the gonofurca. The larva differs from those of the majority of the related species in the presence of only one row of the inner mandibular spines. Records of two species, Helodon ferrugineus (Wahlberg, 1844) and Stegopterna trigonia (Lundstrom, 1911), identified from a few early-instar larvae, need confirmation. The type material of the new species is deposited at the Zoological Institute, Russian Academy of Sciences, St. Petersburg.