Jem stopped Scout from killing a roly-poly. Relate this to the major theme of the book.

The roly-poly incident is yet another example of Jem's increasing maturity. Having witnessed Tom's trial and his family's reaction of his death, Jem has an even greater sense of the need to protect the innocent. Therefore, the roly-poly bug is a symbol of the weak and oppressed who are often "stomped on" by society. Jem believes in the equality of all people, and his choice to protect the roly-poly demonstrates how deeply ingrained this value is. Jem is becoming a young man of honor and moral virtue, just like his father. The theme this incident relates to is that of the mockingbird.