Forgive the short dip into Philosophy 101 here, but we promise – it'll pay off in the end.
A major German Enlightenment philosopher by the name of Immanuel Kant came up with the ethical principle that you should act toward others as if your actions served as a universal law applicable to everybody, including yourself (read more). This is called the categorical imperative. It's another way of saying that you should do unto others as you would have them do unto you. But Kant also elaborated on this idea by saying that you should always act toward others with respect for their humanity.
Why are we bringing up Kant here? Well, given that Kafka was an educated, German-speaking Czech Jew, it's not hard to see echoes of Enlightenment philosophy in his works. But more importantly, Kafka puts a twist on this whole ethical tradition by making the subject of ethical debate in The Metamorphosis a bug. And not just any bug – a vermin, a pest. Gregor isn't a cute little ladybug or even a motherly spider named Charlotte, but the kind of disgusting bug that makes your skin crawl and stinks when you squish it.
So what happens to ethics when the subject is a bug? Should we do unto vermin as we would have vermin do unto us? What if we can't determine what Gregor is exactly, human-vermin hybrid that he is? Which laws apply to Gregor? These are the questions that the story pursues under the key term "consideration": both Gregor and the family struggle to determine what it means to be considerate to one another and what considerations they are ethically bound to give one another.
Gregor's literal transformation into a bug is actually a metaphor for the immoral person that he is: a dishonest, lazy employee, an irresponsible son, and a lewd man.
Kafka's Metamorphosis satirizes the characters' constant appeal to consideration by showing how inconsiderate they are.