At one point in the story of The Water Cure, two of my characters discuss a phenomenon they have seen with their own eyes, and dismiss fireflies as an explanation for it. Fireflies, as everyone knows, glow yellow-green; not blue.

Well, in fact, there is a species of firefly that glows blue. But it is not indigenous to the Ozark Mountains where my characters encounter that light. It’s found, instead, in the Great Smoky Mountain range — close to where one of those two characters was born!

Read about rare “Blue Ghost Fireflies” in this article from Discovery Magazine:

https://www.discovery.com/nature/rare-blue-ghost-fireflies-only-glow-in-one-part-of-north-america