Albert Barnes Commentary Exodus 8:2

"And if thou refuse to let them go, behold, I will smite all thy borders with frogs:" — Exodus 8:2 (ASV)

With frogs — Some months appear to have elapsed between this and the former plague, if the frogs made their appearance at the usual time, that is, in September. The special species mentioned here is of Egyptian origin.

This plague was, like the preceding, in general accordance with natural phenomena, but marvelous both for its extent and intensity, and for its direct connection with the words and acts of God’s messengers. It had also apparently, like the other plagues, a direct bearing upon Egyptian superstitions. There was a female deity with a frog’s head, and the frog was connected with the most ancient forms of nature-worship in Egypt.