Heb. sas (Isaiah 51:8), denotes the caterpillar of the clothes-moth.
The manna bred worms (tola'im), but on the Sabbath there was not any worm (rimmah) therein (Exodus 16:20,24). Here these words refer to caterpillars or larvae, which feed on corrupting matter.
These two Hebrew words appear to be interchangeable (Job 25:6; Isaiah 14:11). Tola'im in some places denotes the caterpillar (Deuteronomy 28:39; Jonah 4:7), and rimmah, the larvae, as bred from putridity (Job 17:14; 21:26; 24:20). In Micah 7:17, where it is said, "They shall move out of their holes like worms," perhaps serpents or "creeping things," or as in the Revised Version, "crawling things," are meant.
The word is used figuratively in Job 25:6; Psalms 22:6; Isaiah 41:14; Mark 9:44,46,48; Isaiah 66:24.
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Worm'". "Easton's Bible Dictionary".