News Release

Sex is the ultimate risky business (for flies in bat territory, that is)

Peer-Reviewed Publication

Cell Press

Sex Is the Ultimate Risky Business (for Flies in Bat Territory, that Is) (1 of 2)

image: This shows Natterer's bat. view more 

Credit: Siemers et al., <i>Current Biology</i> Volume 22 Issue 14

If you are a fly living with bats in a cowshed, sex really could be the death of you. That's according to a study in the July 24th issue of Current Biology, a Cell Press publication, showing that bats eavesdrop on the sounds of fly sex to earn themselves a super-sized dinner deal: two flies for the price of one.

The study is the first to show that increased conspicuousness to hungry predators is a significant cost of sex, the researchers say.

"When mating, the flies utter a burst of broadband, click-like signals, likely from the male's wing-fluttering," said Stefan Greif of the Max Planck Institute for Ornithology. That buzzing sound apparently gives the flies away to bats, which are otherwise completely unable to detect the insects where they sit on cluttered ceilings.

The researchers knew from the start that the Natterer's bats they were studying do eat lots of flies. The question was how those diurnal flies landed in bat bellies when they should be essentially invisible to the bats, given the bug hunters' reliance on echolocation.

To find out what was happening, the researchers started filming in the perfect setting—a cowshed that was home to a bat colony and more flies than anyone could count. Those videos show that flies are extremely reluctant to fly at night, and that bats almost never attack flies that are still or walking on the ceiling.

As soon as flies start having sex, however, their risk of being attacked shoots up dramatically. On average across four years and 1,100 observed acts of fly sex, about 5 percent of the flies caught in the act by the researchers were also detected and attacked by the bats. In about 60 percent of those cases, the bat attacker successfully gobbled up both flies for a double meal.

Greif says he suspects other predators might use the same strategy to get themselves a two-for-one dinner deal. "Many animals are not only conspicuous in being vocal during sex, but they are also distracted in their attention," he says. Overall, the take-home message is pretty simple: "Sex kills."

###

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.