Bats avoid fireflies based on their bioluminescence and movements, according to a study published August 22 in Science Advances. Previously, researchers thought fireflies used light only for the purposes of attracting mates.
Researchers forced interactions between the glowing insects and bats that were unaccustomed to the fireflies. The bats initially consumed the bugs, but over time they learned to avoid them.
After the researchers obscured the glowing bits of the fireflies with paint, the bats ate the insects, indicating that bioluminescence was a warning sign. In another experiment, the researchers found that bats did not avoid eating tethered and glowing fireflies to the same extent as they when the insects were free-flying, suggesting that movement was another deterrant.
B.C. Leavell et al., “Fireflies thwart bat attack with multisensory warnings,” Sci Adv, doi:10.1126/sciadv.aat6601, 2018.