It's been awhile since I wrote it and I don't think I have a copy on this PC, but it basically said that Gregor was vermin both before and after his metamorphosis. Gregor chose to work and chose to cut himself off from his family.
Essentially, he stole the meaning of life from each member of his family. Remembering that Kafka was an existentialist author, you realise that this is the actual theme of the book. His father, for example, would typically have had the role of breadwinner, but didn't because Gregor forced his way into that role. As a result, his father was essentially withering away into nothingness due to a complete lack of meaning behind his life. He wanted to send her to music college without her ever asking to if I remember rightly, forcing his own meaning onto someone else. I can't remember what I wrote for the mother.
Even when he turned into a bug, all he did was try and find ways back into his stolen meaning. He wanted his sister to play for him and him only, hoping to steal her current, happy existence of playing to lodgers. He eventually scared the lodgers away, too, in an attempt to steal back his position.
And when he finally dies, no different than he ever was (Metamorphosis is an ironic title as he has only ever changed in physical form), his family is finally free and they are able to act as they have always been able to act, but they are now no longer constrained by Gregor and his passive-aggressive control.