双头蛇（Amphisbaena，「两个方向进行」之意，亦称为amphisbaenae、amphisbaina、amphisbene、amphisboena、amphisbona、amphista、amphivena或anphivena）是一种起源于博物志，身体两边都有头的怪物。这种怪物可以同时向两个方向行动，还可以向两方掠食动物。双头蛇的两个头在合作无间时是很可怕的猎人，但意见相左就会为自己带来厄运。在西方的徽章及纹章学，双头蛇是常见的一个图案，类似的生物还有飞龙、衔尾蛇等。神话中的双头蛇在外型上和基因突变造成的双头蛇完全不同。

The amphisbaena (/ˌæmfɪsˈbiːnə/, plural: amphisbaenae) is a mythological, ant-eating serpent with a head at each end. The creature is alternately called the amphisbaina, amphisbene, amphisboena, amphisbona, amphista, amfivena, amphivena, or anphivena (the last two being feminine), and is also known as the "Mother of Ants". Its name comes from the Greek words amphis, meaning "both ways", and bainein, meaning "to go". According to Greek mythology, the amphisbaena was spawned from the blood that dripped from the Gorgon Medusa's head as Perseus flew over the Libyan Desert with it in his hand, after which Cato's army then encountered it along with other serpents on the march. Amphisbaena fed off of the corpses left behind. The amphisbaena has been referred to by various poets such as Nicander, John Milton, Alexander Pope, Percy Bysshe Shelley, Alfred, Lord Tennyson, and A. E. Housman; as a mythological and legendary creature, it has been referenced by Lucan, Pliny the Elder, Isidore of Seville, and Thomas Browne, the last of whom debunked its existence.