Vipera aspis is widespread in Italy, with three different subspecies. The species is highly polymorphic and melanistic individuals are often observed in every clade. The darker skin pigmentation provides clear thermal benefits for populations living in cold environments; in addition, it protects from UV damage. Melanism, on the other hand, reduces predatory efficiency and makes the vipers more conspicuous to potential predators.

The Italian territory is key for the asp viper, but scarce information is available about the distribution and ecology of melanistic individuals. On the latest issue of Acta Herpetologica, a detailed study fills this gap. By combining field observations, scientific literature and rigorously selected data from citizen science projects, the authors describe the geographical distribution of melanistic individuals in three subspecies of V. aspis (V. a. aspis, V. a. Francisciredi and  V.a. hugyi). In addition, they analyze the correlation between darker pigmentation and bioclimatic conditions, to explore niche preferences and to model the possible presence of other melanistic populations in Italy. 

The study reveals that melanistic individuals of V. aspis inhabit higher elevations and have a narrow altitudinal range than individuals with a lighter coloration. Indeed, they are restricted to temperate regions in the Alps and in the Apennines. The presence of asp vipers with dark skin pigmentation is strongly influenced by elevation and mean annual temperature. Forested areas are preferred by melanistic individuals, which may obtain antipredatory advantages by hiding in shadowed microhabitats. 

Mean solar radiation, precipitation patterns and mean diurnal temperature range seem to affect the distribution of melanistic vipers as well, with every analyzed subspecies showing distinctive bioclimatic preferences. However, the observed pattern could be an artifact of different bioclimatic conditions available at different latitudes along the Italian peninsula. Altitude can act as a confounding factor as well, by homogenizing bioclimatic conditions. Therefore, finer scale bioclimatic studies are still needed to obtain a reliable characterization of microhabitat partition for melanistic individuals of each subspecies.

Finally, niche modeling reveals that other suitable areas for melanistic vipers exist in Italy. However, despite intense sampling effort in such areas, no individuals have been observed in such areas so far. In conclusion, further field surveys are essential to better understand the ecological dynamics and confirm the presence of melanistic vipers in other suitable areas identified by the niche modeling.

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