Albert Barnes 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)

The locusts - The locust is less common in Egypt than in many eastern countries, yet it is well known, and dreaded as the most terrible of scourges. They come generally from the western deserts, but sometimes from the east and the southeast. No less than nine names are given to the locust in the Bible, of which the word used here is the most common (ארבה 'arbeh); it signifies “multitudinous,” and whenever it occurs reference is made to its terrible devastations.