Isaiah 66:23-24 And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith the LORD. And they shall go forth, and look upon the carcases of the men that have transgressed against me: for their worm shall not die, neither shall their fire be quenched; and they shall be an abhorring unto all flesh.

I believe it is referring to the Millenium. If so, this is not referring to the lake of fire yet - though from Mark 9 and this passage, we know that the worms will also be gnawing on them forever.

Isaiah 14 also refers to worms in Hell.

Isaiah 14:9-12 Hell from beneath is moved for thee to meet thee at thy coming: it stirreth up the dead for thee, even all the chief ones of the earth; it hath raised up from their thrones all the kings of the nations. All they shall speak and say unto thee, Art thou also become weak as we? art thou become like unto us? Thy pomp is brought down to the grave, and the noise of thy viols: the worm is spread under thee, and the worms cover thee. How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations!