Bumblebees have been caught by nightfall, and the poem simply watches them. They are clinging to a bull thistle, a prickly plant the speaker calls "that bed of nails," and they are held in a strange in-between state: "lifeless but not dead, / sleepless but very far from waking." The cold has switched them off without ending them.
What gives the poem its quiet ache is the last image. Above the bees, the sky is full of stars, which the speaker describes as "vast meadows that blaze." The bees spend their lives among flowers, yet now they hang beneath a field of light they can't see or reach. The comparison makes the sky feel like the place they belong, just out of range.
The speaker doesn't state a feeling outright. Still, the tender phrase "mother of bumblebees" and the careful, hushed tone suggest affection and a little wonder. The mood is still, cold, and gently sad, with a sense of fragile life waiting out the dark.