The title does a lot of the work here. A starving artist is thinking about eating insects, and the poem's four short lines show what that thought does to his sense of himself. He has spent the whole day watching light, insects, and other small creatures. Then comes the odd, quietly funny final phrase: they are creatures "to which / I was not little."
That line is the heart of the poem. Normally a person is far bigger than a beetle or an ant. Here the speaker seems to see himself on their level, or at least no longer far above them. Hunger may be making him feel small, weak, and close to the things he might have to eat. The poem suggests he is both an observer, like an artist, and a possible predator, and that these roles blur.
The mood is quiet, dry, and a little wry. There's no panic, only a calm, strange humility. The spare lines leave the speaker looking small and a bit absurd, but also very attentive.