Why does Walter say, "Bitter? Man, I'm a volcano. Bitter? Here I am a giant- surrounded by ants!"? What does he mean by this exclamation?

George tells Walter that he is full of bitterness. Walter gets angry saying that only he has the foresight to make money: to each out and grab what is his. He thinks he is the only person that has big plans while the other members of the family run around, like ants, planning to waste the insurance money.