The Numbers context seems to refer to a poisonous viper living in the desert regions around Biblical Moab. It has been identified tentatively with Heb. אֶפְעֶה, H704, which is, in turn, identified with Echis carinatus, “a viper living in sandy plains” (“Serpent,” IDB).
In other usages, the term saraf refers to legendary creatures (e.g. the flying serpents of
G. E. Post, “Serpent,” HDB (1905); F. S. Bodenheimer, “Serpent,” IDB (1962).
International Standard Bible Encyclopedia (1915)
See Serpent, 3, (2).