Jamieson, Fausset and Brown on Job 18:13

13. Umbreit has "he" for "it," that is, "in the rage of hunger he shall devour his own body"; or, "his own children" (La 4:10). Rather, "destruction" from Job 18:12 is nominative to "devour."

strength--rather, "members" (literally, the "branches" of a tree).

the first-born of death--a personification full of poetical horror. The first-born son held the chief place (Ge 49:3); so here the chiefest (most deadly) disease that death has ever engendered (Is 14:30; "first-born of the poor"--the poorest). The Arabs call fever, "daughter of death."