Little is known about the terrestrial colubrid Psomophis Genimaculatus (BOETTGER, 1885), which inhabits the plains of East Bolivia, Southwest Brasil, West Paraguay and North Argentina; so, for this small snake, treated long time as synonym of the species joberti, only few records exist for the Paraguayan Gran Chaco. In this short note we provide additional data on its morphology, habitat and ecology in the Chaco of Paraguay. Further, we focus on an interesting defensive behaviour of that species, namely to sting with its tail tip, which is also discussed in the background of traditional records.