The Black Death (or Bubonic Plague), a disease that wiped out about a third of Europeans around 1350, was carried by the "oriental rat flea," a parasite of black rats. Its scientific name is Xenopsylla cheopis (source).
What is it about the image of a flea biting a woman's pale flesh that turned certain male artists on? Images of fleas appear in several artistic works besides Donne's poem, including this eighteenth-century painting by Giuseppe Maria Crespi (source).
John Donne coined more new words in the English language than even Shakespeare. Click here to find out which two authors coined even more.