In this study we identified adults of Tenebrionidae associated mainly with pig carcasses and human cadavers lying in different arid and semiarid areas of Argentina. This article provides an illustrated key to 29 Tenebrionidae species of the potential forensic importance, accompanied by diagnoses, and habitus photographs of these taxa. The recorded species of darkling beetles belong to four subfamilies: Alleculinae (one species of Alleculini), Diaperinae (two species of Crypticini), Tenebrioninae (15 species, ten belonging to the tribe Scotobiini, three to Opatrini, two to Alphitobiini and one species of Tenebrionini), and Pimeliinae (10 species, three belonging to the tribe Epitragini, two to Evaniosomini, two to Praociini, one species from each of the tribes Trilobocarini, Edrotini and Elenophorini). A new species of Eutelocera Solier (Pimeliinae: Praociini) collected from decomposing pig carcasses is described: E. cadaverina Flores and Zanetti sp. nov. Two species are new records for Argentina: Conibius (Gondwanodilamus) franzi Kaszab and Alphitobius laevigatus (Fabricius); three species for Bolivia: Blapstinus punctulatus Solier, Salax lacordairei Guérin-Ménveille, and Vaniosus profana (Kulzer); and one species for Uruguay: Blapstinus punctulatus Solier. A discussion is presented on the potential forensic importance of some species collected from human cadavers and pig carcasses.