Else, if thou refuse to let my people go
He threatens him with the following plague, the plague of the locusts, which Pliny F24 calls "denrum irae pestis":
behold, tomorrow will I bring the locusts into thy coast;
according to Bishop Usher F25 this was about the seventh day of the month Abib, that this plague was threatened, and on the morrow, which was the eighth day, it was brought; but Aben Ezra relates it as an opinion of Japhet an Hebrew writer, that there were many days between the plague of the hail, and the plague of the locusts, that there might be time for the grass and plants to spring out of the field; but this seems not necessary, for these locusts only ate of what were left of the hail, as in the following verse.