He spoke, and there came swarms of flies, and gnats in all their country.
Read Chapter 105
Augustine of Hippo
AD 430
21. "He spake the word, and there came all manner of flies, and lice in all their quarters" (ver. 31). If it be asked when He spake, it was in His Word before it took place; and there it was, without time, at what time it should take place: although even then He commanded it to be done, when it was to be done, through Angels, and through his servants Moses and Aaron.
Flies. This was revealed to David, or known by tradition, as it is not recorded by Moses. (Worthington)
Some copies of the Septuagint have, "the dog-fly "cinifes (Exodus viii. 16.) gnats, (Haydock) which are very common and tormenting in Egypt. The Jews understand lice. (Joseph and the Chaldean) (Calmet)