Here, the speaker, in characteristic hyperbole, seems to claim that, if the mistress doesn’t have sex with him, she will remain a virgin forever – an idea he clearly holds in contempt. Think back to his initial accusation that her "coyness" is a "crime." Here, he describes her punishment – worms! That’s not very nice – although, if you have a dark sense of humor, it can be funny, too. The lines also draw attention to themselves by rhyming "try" with "virginity," which causes us to think about what we are reading.