I seem to recall there's a midrash somewhere that it was originally a plague of frogs, then when they all died they died in a pile and merged into one mighty huge megafrog
An amorphous, toad-like god-creature mentioned in the Pnakotic Manuscripts and the Necronomicon and the Commoriom myth-cycle preserved by the Atlantean high-priest Klarkash-Ton, breeding like crazy in lower Egypt?