Collier's New Encyclopedia (1921)/Adder
ADDER, etymologically nadder, the n having been attracted to the article and lost, the common English name of the viper (Vipera berus) . Its color is yellowish brown or olive, with a double series of black spots along the back. The sides are a little paler and are also spotted with black. The adder has a broad, triangular head and a short tail. It rarely exceeds two feet in length. The adder is the only poisonous reptile in Great Britain, and is found in most of the countries of Europe. In the United States the name is popularly applied to several harmless snakes, but the true adder does not occur.