Reference
Luca M. Luiselli, Lorenzo Rugiero (1990): On habitat selection and phenology in six species of snakes in Canale Monterano (Tolfa Mountains, Latium, Italy) including data on reproduction and feeding in Vipera aspis francisciredi (Squamata: Viperidae) – Herpetozoa – 2_3_4: 107 - 115.