Adder Snake - Adder Poisonous snake of the viper family. In Great Britain the only venomous snake is the adder. Adult can usually recover from the effects of its bite. In Africa are found the related puff and night adder. The names puff adder and spreading adder are sometimes applied to the harmless hog-nosed snake of North America . The death adder of Australia and the Krait of India, which is often called the Blue adder, are related to the Cobra .