Here's one way bats might get their next meal: by eavesdropping on flies having sex. Bats eat a lot of seemingly undetectable flies. To find out how the winged mammals find the insects, researchers set up a video camera inside a cowshed that was home to a bat colony and lots of bugs. The video showed that bats rely on their echolocation skills to detect flies at a specific time: when they're engaged in rather noisy sex. Flies are usually quiet in bat territory and sit on cluttered ceilings in caves where backround noise masks the echoes from their movement. But when flies are feeling frisky, males can't help but flutter their wings, emitting a burst of click sounds that the bats pick up on. During more than one thousand sexual encounters caught in the act on video, five percent of the insects were caught in the act by bats. The research is published in the journal Current Biology. The study shows that ignorance can be safer than carnal knowledge when predators are on the prowl.