What is the importance of caterpillars and butterflies in the novel, What the Fireflies Knew?

Caterpillars and butterflies are symbols of transition. Throughout the novel, KB collects caterpillars, and during the times when Nia is willing to partake in childish activities with her sister, she does too. Both the sisters are changing, however, and a symbol of this is when Nia gets out of the shower wrapped like a cocoon, and KB physically attacks her. KB is fighting against the person that Nia is trying to become.