Albert Barnes Commentary Psalms 104:20

"Thou makest darkness, and it is night, Wherein all the beasts of the forest creep forth." — Psalms 104:20 (ASV)

Thou makest darkness, and it is night - You have made arrangements for the return of night—for the alternations of day and night. The Hebrew word rendered “makest” means “to place;” and the idea is that God constitutes the darkness, or so disposes things that it occurs.

Wherein all the beasts of the forest - The margin is, “the beasts thereof do trample on the forest.” The reference is to the beasts that seek their prey at night.

do creep forth - The Hebrew word used here properly means “to creep,” as the smaller animals do that have feet (e.g., mice, lizards, crabs), or as those do that glide or drag themselves upon the ground, having no feet (e.g., worms and serpents). (Genesis 1:21, Genesis 1:26, Genesis 1:28, Genesis 1:30; Genesis 9:2). The allusion here is to the quiet and noiseless manner in which the animals come forth at night in search of their prey, or seem to crawl out of their hiding places—the places where they conceal themselves in the daytime. The idea is that the arrangements that God has made in regard to day and night are wisely adapted to the animals that he has placed on the earth. The earth is full of animated beings, accomplishing by day and night the purposes of their existence.