A butterfly is dressed like an African queen, then ends up on a clover leaf looking as though it has run a race. That sudden drop from splendor to weariness is the whole story of Emily Dickinson's six lines, and it holds the poem's central idea: the most dazzling surface can sit on top of fragility, or at least look as if it does. The final line, "As if it were undone," keeps us unsure which.
The first three lines build an image of near-invincibility. "Numidian" points to Numidia, the ancient North African region, so the butterfly's wings arrive with an air of distant empires and exotic cloth. The word "Gown" turns a insect into royalty. Then comes the surprising verb phrase "roasted on." Dickinson does not say the spots are painted or stitched. The "spots of Burnish" are fired onto the wing like glaze on pottery or polish on metal, so the pattern seems made by heat. This sets up the claim that the gown "Is proof against the Sun," where "proof" carries the sense of armor, as in "bulletproof." Fire made the dress, so fire cannot harm it.
Then the poem turns on one small word, "Yet." The grammar is interesting here. The subject is still the gown, yet it is "prone to shut its spotted Fan." Clothing and creature blur together, as if the dress itself were tired. The wings become a lady's fan, and "spotted" echoes the earlier "spots," tying the two images together. "Prone" also suggests lying flat, so the word hints at the collapse before it happens. By "panting on a Clover lean," the grand imagery has shrunk to a humble plant and a body short of breath. Judging by the imagery, the "Sun" that could not defeat the gown has still worn out the wearer.
The last line gives "undone" at least two meanings. A gown can be undone like a loosened fastening, so the butterfly looks like someone stepping out of a formal dress after a long hot evening. A person can also be undone like someone ruined or overcome. Dickinson's "As if" matters most, because it admits that this is how things look to the observer. The butterfly may be resting rather than defeated, and its "panting" may be our projection. The poem holds the contradiction without settling it.
The form does quiet work. Every line ends on an n sound: Gown, on, Sun, Fan, lean, undone. This gives the poem a low hum, like a held breath. Only "Sun" and "undone" are full rhymes, and they fall on the two shortest lines. As I scan it, the lines run roughly four stresses, four, three, four, four, three: "With SPOTS of BURnish ROASTed ON" is steady and ceremonial, while "Is PROOF aGAINST the SUN" and "As IF it WERE unDONE" end the two halves more briefly. The first short line states the claim of invulnerability, and the second quietly undoes it. The poem has almost no punctuation, apart from a dash at the end, and its single sentence pours down the page with little pause. Capitals on Gown, Burnish, Sun, Fan and Clover make each object feel like a small named character.
What makes the poem worth reading is how much it does with so little. Dickinson often turns a close look at a small creature into something larger, and here a butterfly lets her explore vanity, protection and exposure in under forty words. The vocabulary of empire, fire and fashion is enormous for an insect, and the mismatch is part of the humor. It is also part of the tenderness, because the grand words make the butterfly's panting look more touching. Anyone who has worn their best clothes in the heat, or put on a confident face and then slumped when nobody was watching, will recognize the scene.