Exodus 10:19-21

19So the Lord shifted the wind to a violent west wind which lifted up the locusts and drove them into the Red Sea; not one locust remained within the border of Egypt.

20But the Lord hardened Pharaoh’s heart [so that it was even more resolved and obstinate], and he did not let the Israelites go.

21Then the Lord said to Moses, “Stretch out your hand toward the sky, so that darkness may come over the land of Egypt, a darkness which [is so awful that it] may be felt.”