In just three short lines, this haiku-like poem gives a tiny creature a very human feeling: boredom with who it is. The title, "Swallowtail," tells us what the caterpillar will become, a butterfly. That context makes the final line funny and a little touching, because the caterpillar seems to be longing for change.
The first line, "big fake stare," most likely points to the eyespots that some swallowtail caterpillars have, which look like large staring eyes meant to scare off predators. The word "fake" matters here. The caterpillar is putting on a front, pretending to be something fiercer than it is. Then the poem drops the act: it is tired of being a caterpillar.
The mood is light and wry, with a hint of weariness underneath. The speaker doesn't seem to mock the caterpillar so much as sympathize with it. Anyone who has felt stuck in a stage of life and ready to move on can recognize that feeling.