Symbolism, Imagery, Allegory
In the opening scene of the novel, Bigger has to deal with a disgusting rat in his family’s one-room apartment:
"There he is!" the mother screamed again.
A huge black rat squealed and leaped at Bigger’s trouser-leg and snagged it in his teeth, hanging on.
"Goddamn!" Bigger whispered fiercely, whirling and kicking out his leg with all the strength of his body. The force of his movement shook the rat loose and it sailed through the air and struck a wall. Instantly, it rolled over and leaped again. Bigger dodged and the rat landed against a table leg. With clenched teeth, Bigger held the skillet; he was afraid to hurl it, fearing that he might miss. The rat squeaked and turned and ran in a narrow circle, looking for a place to hid; it leaped again past Bigger and scurried on dry rasping feet to one side of the box and then to the other, searching for the hole. Then it turned and reared upon its hind legs. (1.39-47)
His response is to throw a shoe at the rat and kill it: which, fair enough. We would probably just jump on top of the table and start shrieking, but that's us. We're weenies.
This rat is important on a few levels. Superficially, the rat shows us the kind of squalor that Bigger and his family are forced to live in: crowded apartments that are overrun with vermin. Not pretty.
But some critics argued that the rat is a symbol of Bigger himself—the rat comes into the domestic sphere of the Thomas house and is killed and Bigger comes into the domestic sphere of the Dalton household and (ultimately) is killed.
This scene also potentially foreshadows Bigger’s confrontation with the disgusting, penetrating racism in American society. The forces of racism permeate American society in the same way that pests overrun houses. And, though Bigger doesn’t kill those forces in American society itself, he does manage to obliterate them within himself and, we hope, in the novel’s reader.
Also, a discussion of vermin in a book about racism wouldn't be complete without an analysis of how racism works. Racist ideology has a tendency to cast the object of the racism—in Native Son's case, black Americans—as "lesser than" and "malicious." This often rears its ugly little head by casting the object of racism as animals, especially pests. Like, say... rats.