What is the symbolism of "the flea" in Donne's poem, The Flea?

The flea symbolizes sexual and spiritual union. The speaker argues that, by biting both himself and the beloved, the flea has "married" them already as it holds both their blood inside its body. At the same time the flea is an insignificant and innocent creature, the speaker argues that it is also a sacred object that has brought them together. The flea becomes an example of Donne's reliance on paradox as he straddles the line between portraying the flea as small and negligible as well as sacred and momentous.