Exodus 8:21-22

Else, if thou wilt not let my people go, behold, I will send swarms {of flies} upon thee, and upon thy servants, and upon thy people, and into thy houses: and the houses of the Egyptians shall be full of swarms {of flies}, and also the ground whereon they {are}. {swarms...: or, a mixture of noisome beasts, etc} And I will sever in that day the land of Goshen, in which my people dwell, that no swarms {of flies} shall be there; to the end thou mayest know that I {am} the LORD in the midst of the earth.