Numbers 21:6

Fiery serpents. They are so called, because they that were bitten by them were burnt with a violent heat. (Challoner) --- Hence they are called seraphim, by which name an order of angels are known. The Egyptians adored a serpent which they called serapis, at Rome; and they represented their god serapis, with a serpent entwining a monstrous figure, composed of a lion, a dog, and a wolf. (Macrobius, Saturn i. 20.) The seraph was a winged serpent, Isaias xiv. 29. xxx. 6. Such often infested Egypt, in spring, coming from Arabia, unless they were intercepted by the ibis. Their wings resembled those of bats. (Herodotus, ii. 76.; Mela, &c.) God probably sent some of this description into the camp of the Israelites. (Calmet) --- Some call them pr\'9cster, (Pliny, [Natural History?] xxiv. 13,) from their burning; others the hydra, or, when out of water, the chershydra, the venom of which is most dangerous. The Septuagint style them simply, "the destroying, or deadly serpents." See Bochart, T. ii. B. iii. 13.; Deuteronomy viii. 15.; Wisdom xvi. 5, 10.) (Haydock)