שמות ח ,ג : וַיַעֲלוּ אֶת־הַצְפַרְ דְ עִים
Unlike most commentators, the Sforno maintains that the צְפַרְ דְ עִים were not frogs but were crocodiles.
In later verses this is a subtle change in Paroh’s request and Moshe’s initial response. In verse 4, Paroh asks that the crocodiles be removed. Whereas, Moshe speaks of their destruction in verse 5. However, in verse 6 Moshe states “according to your word” as you originally requested, there would be a removal and not a destruction. Therefore, the Sforno is of the opinion that the crocodiles only now took up their habitation in the Nile at the command of HaShem.