a moth: the small insect whose grub eats holes through stored cloth
This word never simply reports that there are insects around. In all seven places it is part of a comparison, and the comparison always turns on the moth: either what it quietly destroys, or how little force it takes to destroy it.
The insect is the clothes moth, and the damage the Bible pictures is done by the grub inside a folded garment, not by the adult fluttering around a lamp. Nobody watches it happen. The cloth is put away whole and taken out full of holes. That hiddenness is what every writer who uses the word is reaching for.
Most often the moth is the one doing the damage. A person wears away like a coat a moth has eaten, and Isaiah twice promises that those who accuse God's servant will be eaten through like clothing. The most startling use is in Hosea, where God says he himself is like a moth to Ephraim: not a lion tearing its prey, but something small and slow that has already been at work for a long time before anyone notices. Two neighboring words keep the same company. A second name for a cloth-eating grub (סָס) stands beside it in Isaiah 51:8, where one eats the garment and the other the wool, and the word for rot (רָקָב) is its partner in both Job 13:28 and Hosea 5:12.
Twice in Job the picture turns around and the moth is the fragile one. People who live in houses of clay are crushed as easily as a moth is, and a wicked man builds his house no more solidly than a moth builds its own flimsy case. It is the same insect and the same slightness; only the direction of the comparison changes.