Bats eavesdrop on the sound of copulating flies
The idea that copulation might increase predation risk is a classic suggestion , but empirical evidence to support it is surprisingly scarce. While some early work found decreased vulnerability to predation during mating , two lab and one very recent field study documented increased predation during mating in freshwater amphipods , water striders  and locusts . Decreased vigilance, less efficient escape responses, and increased conspicuousness of mating pairs have been suggested as mechanisms that might underpin elevated predation risk during copulation . However, these putative mechanisms have never been investigated empirically. Here we describe a bat-insect system within which copulation greatly increases predation risk. We experimentally demonstrate that wild Natterer's bats (Myotis nattereri) eavesdrop on acoustic cues emanating from copulating flies (Musca domestica) in a cowshed (Figure 1). With this evidence, we pinpoint increased conspicuousness as a relevant mechanism for elevated predation risk during mating.