The adder's main prey consists of small mammals such as rats, mice, voles and shrews. They will sometimes also eat larger mammals such as moles. Occasionally they will hunt for lizards or amphibians and they have been known to catch slow worms.
Adder's have been known to climb into shrubs and bushes to raid nests for their eggs or for young birds.
When hunting, adders strike swiftly, delivering a venom-injecting bite to their prey. Then they wait for the prey to die before swallowing it whole. They are able to extend their jaws to swallow prey much bigger than their heads, whilst their ribs are not joined and can also open outwards to accommodate much larger prey. Their digestive juices are very powerful, so only the teeth and hair of a rodent pass through the snake.