The fourth plague is introduced with a vividness the Hebrew keeps restrained. Targum Pseudo-Jonathan on Exodus 8:17 translates the arov — the mixed swarm — as a mixed multitude of wild beasts, and warns that Egyptian houses will be filled with a swarm of wild beasts, and they shall be upon the land also.
Rashi later picks up this reading: not flies, not locusts, but a terrifying convoy of animals from every climate — lions, leopards, wolves, snakes, bears — all pouring into Egyptian cities together. The meturgeman sketches it for us. The wild that Egypt had fenced out for centuries now fills its corridors.
Why this plague? Egypt had turned the natural world into a theology. Animal-headed gods lined its temples. The Targum is now sending that pantheon, unruled, into Egypt's homes. The crocodile, the lion, the jackal — whose images Egypt had carved on its walls — now arrive on their own terms and walk past the carvings.
And there is a careful phrase: the swarm shall be upon the land also. Not only inside the houses. Not only in the palace. On the land — the cultivated fields, the sacred precincts, the trade routes. The boundary between civilization and wilderness has been erased at God's command.
The takeaway: empires domesticate the world and call it gods. God can send that same world in, un-domesticated, any morning He chooses.