When Titus Andronicus appeared in the first folio of Shakespeare’s plays in 1623 it included a ‘new’ scene, not present in the 1597 quarto and possibly not performed in Shakespeare’s lifetime. This scene comprises eighty-six lines and runs to approximately five minutes’ performance time; its inclusion bears little impact on the textual or performative length of the play, and yet it remains one of the most powerful scenes of the drama. This extraordinary scene, known as the fly-scene, or mad scene, not only poses a significant problem to directors, actors and audiences of the theatre – how do you make a fly audible let alone visible? – but most importantly, ‘What purpose serveth the Fly’? Some six years later at the Globe, Jonson turns this iniquitous insect into a consummate actor: the brilliant and vital force of Mosca. Despite the difference between Titus’s organic matter and the more complex symbolic construction of Mosca, the fly, it seems, can be a theatrical prop, a pre-Cartesian anthropomorphic device, a metaphor and a symbol; whether it is riddled with ‘pretty buzzings’, ‘coal-black’ like the Moor or ‘but a poor observer’ like Mosca, the stage imports the fly to prey on the mind, incite petty violence, defy the madness of mutilation or turn the sinner upon himself.