The film begins with Seth's attempt to pick up Veronica by using his teleportation device as a means to entice her to find him interesting. However he doesn't expect her to be a journalist. This scenario reveals that no one is on the surface who he or she appears to be. Thus, Seth's journey from man to fly becomes this physical representation of being turned inside out, and most specifically becoming his creation.
Seth is a genius, someone capable of changing the world with his technology, but Cronenberg shows us how thinly veiled the line between genius and monster is. Seth is a man who appears to have a great deal of heart and sensitivity, but as the plot carries on and he begins to transform into the fly he loses his compassion with his primal instincts taking over rather than his reasoning mind. The fly in this film represents the birth of the deformity that potentially lies dormant and waiting to get out in us all. Everyone has a desire or a dream they are reaching for; it is the price and extent to which they are willing to sacrifice the good in them for "progress" that changes them. Seth's obsessive desire to change the world becomes a desperate desire to save his own humanity, even by attempting to fuse himself with Veronica and their unborn child.
This is a cautionary tale of the need for limits and boundaries. That the genius mind cannot be left to stir itself, it must be accompanied by others who are capable of recognizing the monster within coming forth in order to keep it at bay while the progress can occur, just at a less rapid pace. The horror of the film is that it is only when Seth is completely transformed, part fly, part metal object that he sees the monster he has become and it is too late to change.
