The Flea is an erotic metaphysical poem (first published posthumously in 1633) by John Donne (1572-1631). The exact date of its composition is unknown.
The poem uses the conceit of a flea, which has sucked blood from the male speaker and his female lover, to serve as an extended metaphor for the relationship between them. The speaker tries to convince a lady to sleep with him, arguing that if their blood mingling in the flea is innocent, then sexual mingling would also be innocent. His argument hinges on the belief that blood mixed during sexual intercourse.
Donne is able to hint at the erotic without explicitly referring to sex, using images such as the fly that "pamper'd swells" with the blood of the lady (line 8). This evokes the idea of an erection. The speaker complains that "This is more than we would do!" (line 9).
Inside the flea is represented the trinity, or the three persons of the godhead; the Father, Son and Holy Spirit as conceived in orthodox Christian belief. The number three throughout the poem works as a symbol of "all in one" and also alludes to the three anatomical sections of an insect - head, thorax, and abdomen. For this reason, the speaker claims it would be "sacrilege" to kill the flea. He holds the flea up in the second stanza as "our marriage bed" and "our marriage temple," begging for the lady to spare its innocent life (line 13). He argues that by killing the flea, she would be killing herself, himself, and the flea itself, "Three crimes in killing three" (line18). The lady, in the third stanza, kills the flea, presumably rejecting the speaker's advances. He then claims she will lose no more honor when she decides to sleep with him than she did when she killed the flea.