Because they had sent the Israelites forth into the fields, to plough and sow, hail was sent down upon them, and their trees and crops were destroyed.
They had been in the habit of saying to the Israelites, "Go forth, plant ye trees for us, and guard the fruit thereon." Therefore God brought the locusts into the Egyptian border, to eat the residue of that which was escaped, which remained unto them from the hail, for the teeth of the locust are the teeth of a lion, and he hath the jaw teeth of a great lion.