The frogs died. And they gathered them on heaps God could as easily have dissolved them into dust, but he would have them to lie dead before their eyes, as a token that they were real frogs and no illusion, and as a testimony of his wonderful power.
Related Commentaries of Exodus 8:13
Exodus 8:13-14
13 And the LORD did according to the word of Moses; and the frogs died out of the houses, out of the villages, and out of the fields.
14 And they gathered them together upon heaps: and the land stank.