The poem is only three lines long, but it packs in a strange, slightly unsettling picture. Something has gotten into the speaker's ear: a bug. The word works on two levels. It could be a literal insect, or it could be the idiom of having a bug in your ear, a nagging idea or a voice that won't leave you alone. The poem never settles it, and that ambiguity is part of its charm.
What the bug brings are "abstract instructions," which sounds like commands that make no clear sense. They aren't practical or specific, just a vague pressure to do something. Then comes the odd, lovely phrase "melancholy feet," as if the tiny creature's footsteps carry sadness as it moves around inside the speaker's head.
The speaker seems more puzzled and quietly weary than panicked. The mood is intimate and eerie, a little humorous, but with a low hum of loneliness running underneath.