You are what you eat, and so is your feces. Well, sort of. Your feces ends up collecting what your body can’t digest, and in the case of insectivorous bats, this can create a dazzling effect.
Insect exoskeletons are made of chitin, which is difficult to digest, similar to cellulose in plants. So as bats eat up to two-thirds of their own body weight in insects each day, their scat becomes a dense collection of insect husks which can sparkle under good lighting conditions.
Why do we know so much about bat poo? It’s not because the sparkles are so entrancing, but because analyzing their guano is the easiest way to track what bats eat, allowing us to better understand how they fit into the ecosystem.
Source: Bats Have Sparkly Poop by Gwen Pearson, Wired