Describe symbolism in The Liars' Club by Mary Karr

A symbol of the endurance of love occurs on the last page of the memoir. As mother and daughter drive home from the Mexican café where all the secrets have been divulged, Mary notices small gatherings of fireflies in the flowers at the roadside: "How odd, I thought, that those bugs lived through the refinery poisons." She is referring to the toxic fumes that emanate from the oil refineries of Leechfield, but she also means for the reader to make the connection: the light of love, like a firefly in the night, continues to live in spite of the toxic atmosphere generated by a quarreling family.