The poem is built around a puzzle: what exactly is the "it" that sits down in the speaker's pool? Clues like "larva," "cocoon," "naked forelimbs," and "one short root" suggest a small insect-like creature, though the speaker also treats it almost like a child or a spirit. It sways, dreams, and calls out "Luna," as if mistaking the speaker for a pale, moon-like parent.
The speaker seems to be both the creature's mother figure and something much larger. The "cousins" who shake the mountain suggest a world of giants, while the creature's own kind are "tiny, earth-bound storms." That shift in scale makes the scene feel dreamlike, tender and a little eerie.
The mood moves from wonder to wistfulness. The closing questions, "Where did it go, that larva? / Did it ever manage to spin / a real cocoon?", sound like someone worrying about a small, vulnerable being they could not protect or follow.