Ehidna
Archimandrite Nikifor’s Biblical Encyclopedia
(adder, viper) (Job 20:16) — a poisonous serpent, some twelve feet or more in length. Its bite is very dangerous, and in most cases ends in swift and inevitable death, so that in ancient times a viper’s bite was regarded as a special punishment from God (Acts 28:1, 6). It is no wonder that the inhabitants of Malta took the Apostle Paul for a god when they saw that the viper hanging from his hand did him no harm. Hence the viper always represents whatever by its nature causes harm and destruction, and is used as a name for cunning, wicked, and godless people.
Hence the Savior’s words addressed to the Pharisees and Sadducees: “generation of vipers” (Matt. 3:7, and elsewhere) — the strongest expression of denunciation of wicked and impious men.