Sometimes all it takes is a bat taking a crap in a bag to yield an interesting discovery. Here's why we underestimated the contribution of the mouse-eared bat to the world, and how science corrected our misconception.
As a species, bats eat everything from fruit to insects to mammal blood. As individuals, though, they tend be very specific, and are loaded up with an arsenal of adaptations to help them catch their food of choice. Although there are omnivorous bats, generally scientists believed that bats that have adapted well enough to eat insects, especially insects in flight, don't or can't turn to fruit in times of need.
At least that was the consensus until researchers were studying the mouse-eared bat in Brazil. It's tough to confirm bat diets, because bats are small, flying, and nocturnal, which form the holy trinity of hard-to-study traits. Researchers were catching the bats in nets and then tagging and releasing them as part of an ongoing project; in between getting the bats out of the nets and putting tags on them, they kept the bats in light silk bags, which kept them grounded but didn't harm them.
After the tagging, they found their lovely new silk bags were covered in bat crap. While it probably depreciated the retail value of the bag, it was a boon to researchers. They'd identified the bat, and the bag was new and uncontaminated, so they could examine the faeces and figure out the bats' dietary habits.
To their surprise, they found fruit seeds. When they painstakingly separated the seeds and planted them (science is oh-so-glamorous), 40% of them sprouted. The mouse-eared bat has always been considered strictly an insect-eater. Now it seems that it's also a fruit-eater that has probably been spreading seeds all over Brazil.