John Gill Commentary Hosea 5:12

"Therefore am I unto Ephraim as a moth, and to the house of Judah as rottenness." — Hosea 5:12 (ASV)

Therefore [will] I [be] unto Ephraim as a moth
Which eats garments, penetrates into them, feeds on them privately, secretly, without any noise, and gradually and slowly consumes them; but at last utterly, that they are of no use and profit: this may signify the various things which befell the ten tribes in the reigns of Zachariah, Shallum, Menahem, Pekahiah, and Pekah, which secretly and gradually weakened them; and the utter consumption of them in the times of Hoshea by Shalmaneser:

and to the house of Judah as rottenness ;
as rottenness in the bones, (Proverbs 12:4) ; which can never be got out or cured; or as a worm that eats into wood, as Jarchi interprets it; and gets into the very heart of a tree, and eats it out: thus the Lord threatens the house of Judah, or the two tribes, with a gradual, yet thorough, ruin and destruction.