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Bats Listen for the Sounds of Fly Sex

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“There are certain rules that one must abide by in order to successfully survive a horror movie,” Randy told us in Scream. “For instance, Number One: You can never have sex. Sex equals death, OK?”

He’s right. For some reason, sex often draws out slasher movie villains, and when supporting characters hook up, they often also get chopped up. The connection between sex and death isn’t just a horror movie trope, though. Biologists have often suggested that animals are at a higher risk for getting killed and eaten during mating, either because they’re more conspicuous, less vigilant, or can’t escape as fast.

For flies, it’s that first factor that’s the problem. Mating can mean certain doom because the sounds they make catch the attention of a killer lurking in the shadows.

In Europe, Natterer’s bats (Myotis nattereri) often roost in barns and cow sheds, drawn by flies that are attracted to animal manure. There’s plenty to eat, but catching the flies isn’t easy. Natterer’s bats hunt by echolocation, generating ultrasonic calls and using the echoes that bounce back to find prey and map their surroundings. Inside the farm buildings, finding flies this way is “almost impossible,” says biologist Stefan Greif, because the faint echoes made by the flies are masked by the more massive ones bouncing back from the walls and ceilings. What’s more, the flies also stop flying around at night, when the bats hunt, and either move around by walking or sit still on the ceiling, making them even harder find. 

Over four years, Greif and his team of researchers filmed thousands of flies walking along the ceiling of a cow shed in Weitershausen, Germany that was home to a colony of 45 bats. In all that time, not one of them was attacked by a bat. Yet, the bats stayed, and Greif knew that flies made up the majority of the species’ diet. So how were they catching bugs that were all but invisible to them?

It turns out that the bats are a little bit like B-movie killers, and make their attacks when the flies are having sex. While flies just walking around were inconspicuous, Greif found that ones that were getting it on were a clear sonic target. This is because when flies mate, the males flutter their wings, producing a burst of click-like noises. Humans can hear the lower frequency noises as a soft buzz, while the higher ones ring as loud and clear to the bats as a dinner bell. More than a quarter of the mating flies that Greif caught on camera during the study were attacked by the bats, and more than half of those attacks were successful, with the bat devouring both flies in all but two cases. 

To make sure that it was the sounds of sex that got the bats’ attention, the researchers tried two experiments. First, they stuck dead flies together in mating positions and mounted them on the ceiling. These were ignored by the bats, so it isn’t the bigger target and larger echo that mating flies create that gives them away. When the scientists recorded the flies’ mating sounds in the second experiment and played them back over a sound system, though, the bats went on the hunt. The researchers watched as “the bats approached, hovered and inspected the speaker, and in several cases tried to glean the acoustically simulated flies from the speaker with their tail membrane—just as they did with real pairs of copulating flies on the ceiling.” 

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Watch a School of Humpback Whales 'Fish' Using Nets Made of Bubbles 

Just like humans, humpback whales catch many fish at once by using nets—but instead of being woven from fibers, their nets are made of bubbles.

Unique to humpbacks, the behavior known as bubble-net feeding was recently captured in a dramatic drone video that was created by GoPro and spotted by Smithsonian. The footage features a school of whales swimming off Maskelyne Island in British Columbia, Canada, in pursuit of food. The whales dive down, and a large circle of bubbles forms on the water's surface. Then, the marine mammals burst into the air, like circus animals jumping through a ring, and appear to swallow their meal.

The video offers a phenomenal aerial view of the feeding whales, but it only captures part of the underwater ritual. It begins with the group's leader, who locates schools of fish and krill and homes in on them. Then, it spirals to the water's surface while expelling air from its blowhole. This action creates the bubble ring, which works like a net to contain the prey.

Another whale emits a loud "trumpeting feeding call," which may stun and frighten the fish into forming tighter schools. Then, the rest of the whales herd the fish upwards and burst forth from the water, their mouths open wide to receive the fruits of their labor.

Watch the intricate—and beautiful—feeding process below:

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