It is the loss of the beloved's innocence symbolized by the flea because <span>later in that stanza, the beloved is obviously represented by the flea. Also the theme of the poem is sex and virtue, the loss of innocence is key.
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The phrase "purpled thy nail" refers to the shared blood of the speaker and his beloved in the flea.
Explanation:
"The Flea" by John Donne is a poem where a lover wants to have premarital sex and in his attempts to convince her beloved one they get bitten by a flea, which he uses as reference of their blood together as one inside of the insect and then when he receives a negative answer and he tries to kill the insect and his lover says that would be sui*cide and a murder because it has their blood in it, he told her that it doesn't have a major importance to kill the insect as it doesn't have it to love each other before marriage.
