What exactly, was the plague of Arov?
Rashi and Targum Yonasan: It comprised a mixture 1 of wild animals, including snakes and scorpions, which killed the Egyptians.
Rashbam: It was a mixture of species of wolves, which generally attack in packs at nighttime. 2
What is the significance of the phrase "and also the ground upon which they are"?
Seforno: This means that the ground upon which the houses stand will be filled with snakes and wild creatures that dwell underground. 1
Divrei Eliyahu, Kol Eliyahu: This hints at the Yid'oni, a ferocious beast attached to the ground by means of a sort of umbilical cord. It too, appeared in Egypt, together with the earth to which it was attached. 2