Definition of "muckworm"

Here you a muckworm of the town might see, / At his dull desk, amid his legers stall'd, / Eat up with carking care and penurie; / Most like to carcase parch'd on gallows-tree.

1748, James Thomson, “Canto I”, in The Castle of Indolence‎

We have painted one Money-Lender — not the mere sordid muckworm of a century ago, but the man-eater of the present day.

1840, Douglas William Jerrold, “The Money-Lender”, in The Writings of Douglas Jerrold‎, published 1853, page 279

Perhaps it is far too expensive for a notorious muckworm like you! I, however, am more generous.

1993, Marlene Suson, The Lily and the Hawk‎, page 158