We analysed a snake species community of a Mediterranean 0.2 ha ecotonal area during a 21 year time span, monitoring two colubrid and one viperid snake species. We carried out analyses in seven years (1997, 1999, 2002, 2004–2005, 2016–2017) that had similar sampling efforts and, in the last two years of short-term monitoring, we applied a recently proposed monitoring protocol of the Italian Environment Ministry. In total, we captured 172 distinct individuals, 61 whip snakes (Hierophis viridiflavus), 26 barred grass snakes (Natrix helvetica) and 85 asp vipers (Vipera aspis). Regarding the long-term monitoring period, whip snakes were captured on average about nine times per year, grass snakes were captured four times per year and asp vipers were found 12 times per year. Captures decreased in whip snakes, while increased in grass snakes and remained constant in asp vipers. In 2016 and 2017, we captured 10 whip snakes, 19 grass snakes and 31 asp vipers. Density estimates of snake species (0.5 H. viridiflavus/ha, 0.3 N. helvetica/ha and 0.7 V. aspis/ha) differ, to a certain extent, from published results for some other areas of central, northern and western Europe, perhaps depending on the approach applied for habitat suitability estimation. The average body size between two years differed neither for whip snakes nor for grass snakes, but it decreased significantly in asp vipers.