International Standard Bible Encyclopedia
moth (`ash; compare Arabic `uththat, "moth"; colloquial, `itt; cac, "worm" (Isaiah 51:8); compare Arabic sus, "worm," especially an insect larva in flesh, wood or grain; ses, "moth" (Matthew 6:19, 20 Luke 12:33); setobrotos, "moth-eaten" (James 5:2)):
The moths constitute the larger division of the order Lepidoptera. Two of the points by which they are distinguished from butterflies are that they are generally nocturnal and that their antennae are not club-shaped. Further, the larva in many cases spins a cocoon for the protection of the pupa or chrysalis, which is never the case with butterflies. The Biblical references are to the clothes-moth, i.e. various species of the genus Tinea, tiny insects which lay their eggs in woolen clothes, upon which the larvae later feed. As the larva feeds it makes a cocoon of its silk together with fibers of the cloth on which it is feeding, so that the color of the cocoon depends upon the color of the fabric. The adult is only indirectly harmful, as it is only in the larval stage that the insect injures clothing. Therefore in Isaiah 51:8, "For the moth (`ash) shall eat them up like a garment, and the worm (cac) shall eat them like wool," both words must refer to the larva, the distich demanding such a word as cac to balance `ash in the first half. The word "moth" occurs 7 times in the Old Testament, in Job, Psalms, Isaiah and Hosea, always in figurative expressions, typifying either that which is destructive (Job 13:28 Psalm 39:11 Isaiah 50:9; Isaiah 51:8 Hosea 5:12) or that which is frail (Job 4:19; Job 27:18).
Alfred Ely Day