Plagues 2-4 are outlined in Exodus 8 because, apparently, Pharaoh was none too worried about a “God” who turned the entire Nile River into blood on command. So God threw some other phenomena at him.
God knew Pharoah wouldn’t be impressed by frogs or gnats or flies either, but other Egyptians would begin to realize the God of the Hebrews was real and a force to be reckoned with.
Learn more in my Exodus 8 video.