Charles Ellicott Commentary Exodus 10:4

"Else, if thou refuse to let my people go, behold, to-morrow will I bring locusts into thy border:" — Exodus 10:4 (ASV)

To morrow will I bring the locusts into thy coast. —Locusts, as already observed, are not indigenous to Egypt, but only occasional visitors. Consequently, they always enter the country from another, such as Nubia, Abyssinia, Syria, or Arabia. Regarding the direction from which the present plague came, see the comment on Exodus 10:13.