The adder's diet is mainly small mammals such as mice, voles, shrews and even weasels and moles. Sometimes, they eat slow worms and lizards. They feed on amphibia, such as frogs, newts, and salamanders. There have been reports of adders eating birds, especially nestlings and eggs. Adders are ovoviviparous. Once they reach about 30 cm (1 ft) in length, their diet becomes adult.