Why does John Steinbeck introduce first seeds and their dissemination, then smaller insects, before reaching the main subject?

This quote is a natural microcosm of the harsh reality going on around it. People, like the Joads and other sharecroppers, are routinely stepped on and abused by people higher on the social hierarchy. Like nature, It is a survive or parish environment:

The sun lay on the grass and warmed it, and in the shade under the grass the insects moved, ants and ant lions to set traps for them, grasshoppers to jump into the air and flick their yellow wings for a second, sow bugs like little armadillos, plodding restlessly on many tender feet.