Few poems can hold a bad mood as neatly as these three lines do. The speaker wakes, and something familiar arrives: "my old temper." Everything before that final phrase is disguise. The poem works by making us watch the temper approach before we learn what it is, so that we feel the same small dread the speaker does.
The first image is "morning warhead," and it is startling because a warhead is the part of a weapon that does the damage. Placing "morning" beside it suggests that the day itself is loaded and about to go off. The second line then undercuts the menace: the thing is "coming in like a moth." A warhead is heavy, fast and deliberate, while a moth is light, erratic and almost silent. The poem asks us to hold both at once, and that is its central idea. Anger can arrive softly, even unnoticed, and still carry destructive force. A moth drifting in through a window does not look dangerous, but the poem warns us not to be fooled by the gentleness of its entrance.
The word "coming" also does quiet work. "Coming in" is the language of incoming fire and of aircraft approaching, but it is equally what we say of a visitor or an insect entering a room. The phrase sits between the two images and links them. The title then adds a third frame, "Unwelcome guest." Now the temper is a visitor who turns up without being invited and who cannot easily be turned away. The metaphors do not match, and they are not meant to. A weapon, an insect and a houseguest crowd into three short lines, which suits a mood that is itself muddled and hard to pin down.
The poem has no rhyme and no fixed meter. By my count the lines run to roughly four, six and four syllables, so the middle line is the longest, as if the moth's slow drift needs more room. This is close to haiku in spirit, though it does not follow the 5-7-5 pattern. It has no punctuation, so the three lines slide into one another and the grammar stays open. We cannot tell at first whether "morning warhead" and "my old temper" are the same thing. Read as a sentence, the last line renames the warhead: the temper is the weapon. Read more loosely, it could be the moth, or even the morning. That ambiguity is useful because it lets the temper blur into the day around it.
Sound ties the lines together. The letter m runs through them, in "morning," "moth" and "my," and gives the poem a low hum, like wings against a lampshade. "Morning" and "warhead" also share a similar vowel, so the two words pull toward each other and make the odd compound feel natural. The last line is the shortest, and the soft sounds of "old temper" bring the poem down from its military image to something domestic and personal. We do not know what the speaker is angry about. The poem's attention is on the anger itself.
The word "old" matters more than it first seems. It tells us this is a temper the speaker has known for years, and the tone suggests recognition more than shock. There is a dry, self-mocking humor in treating one's own worst habit as an insect that keeps finding its way indoors. The possessive "my" is honest too. The temper is called unwelcome, but the speaker admits it belongs to them, so the "guest" turns out to be a resident who has been away and come back.
The poem is significant for how much it does with so little. It turns a private, unglamorous experience, a bad mood at the start of the day, into a small drama of scale and surprise. It also avoids both easy options. It does not make the anger heroic, and it does not dismiss it as trivial. The moth keeps it from becoming melodrama, and the warhead keeps it from becoming a joke. What remains is honest, wry self-knowledge, with the reader left in the moment just before the moth reaches the light.