Charles H. Spurgeon on Psalms 91:13

Dragon. The expression is used (1) for "sea monsters, " (2) for serpents, (3) for wild beasts or birds characteristic of desolate places, and (4) it is used figuratively to represent the enemies of the Lord, and especially Pharaoh, as head and representative of the Egyptian power, and Nebuchadnezzar, the head and representative of the Chaldean monarchy. The term is thus a general one, signifying any monstrous creature, whether of the land or of the water, and is to be set down with the one or the other, according as the context indicates. John Duns, in "Biblical Natural Science."