What is it good for? Absolutely one thing. Luna moths use their tails solely for bat evasion – Research News https://www.floridamuseum.ufl.edu/science/what-is-it-good-for-absolutely-one-thing-luna-moths-use-their-tails-solely-for-bat-evasion/
Scientists have known for about a decade that Luna moths — and other related silkmoths
“They have projections off the back of the hindwing that end in twisted, cupped
