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Gauthier via Wikimedia Commons // CC BY-SA 3.0

Darwin’s Obsession With Barnacle Penises Makes a Lot of Sense Now

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Gauthier via Wikimedia Commons // CC BY-SA 3.0

Barnacle penises are amazing. That’s not a direct quote from Charles Darwin, but it might as well have been; the naturalist was obsessed with the little crustaceans’ very large members. Now scientists say he missed out on one of the best barnacle facts: Many species can change the shape and size of their penises to suit their environment. A report of the findings was published in the journal Integrative & Comparative Biology

Relative to its body size, the barnacle has the largest penis in the animal kingdom. This is, of course, not just some hilarious joke by Mother Nature—the length is necessary in order for these sessile (non-moving) animals to reach one another. Barnacles grow in colonies clamped to rocks, piers, boats, and sometimes large animals like whales. They feed by extending little feathery sensory appendages called cirri into the water to catch plankton. 

In their resting state, barnacles are simultaneous hermaphrodites, meaning that they have both male and female parts. In many species, mating season begins when one barnacle’s egg glands begin to swell, rendering it “functionally female.” That barnacle releases chemicals into the water that tell its neighbors that it’s time to get busy. In response, they become “functional males,” unfurling their long, flexible penises into the water like party horns, questing for the right opening.   

For obvious reasons, these bizarre sexual adaptations fascinated Darwin. The naturalist devoted seven years of his life to studying barnacles, in the process compiling descriptions of the “probosciform” (elephant trunk–like) penises of hundreds of species. (We are not making this up.) 

A small sample of Darwin's barnacle collection. Image credit: FunkMonk via Wikimedia Commons // CC BY 3.0

Darwin was determined to learn all he possibly could about the animals, their anatomy, and their behavior. When he got wind that a friend of a friend had been lucky enough to see barnacle sex in action, he wrote a pretty intense letter, peppering his contact with questions. An excerpt:

Was the probosciformed penis inserted into more than one individual? For about how long [and how many] times was it inserted? Was it inserted deeply & at which end of valves? Especially did the recipient individual continue during the times exerting its cirri? Did it keep its opercula valves widely open for the reception of the organ? I am anxious to know whether this recipient was a willing agent or adulterer. or whether it was a case of rape by act. If the recipient was in full vigour, I think it wd be impossible to insert anything without its consent. Were the specimens under water at times? 

Who was the observer that I might check his authority. 

We told you he was obsessed. But he was far from the only one. Darwin’s love of (and thorough notes on) the lumpy little animals left a scientific legacy that continues to this day. Marine biologists J. Matthew Hoch and Daniel T. Schenk of Nova Southeastern University and Quest University’s Christopher J. Neufeld have spent years studying barnacles. They collected their research—and the findings of others—in the recent review paper, and they came to some very interesting conclusions. 

Barnacle reproductive organs. Image credit: J. Matthew Hoch, Nova Southeastern University

“We know that barnacles are robust in their ability to overcome environmental challenges and to mate successfully,” they write. Sometimes they do that by stretching their penises, making them thicker, or changing their shape altogether. “In the most extreme circumstances,” they say, “it degenerates and is shed during the first post-mating molt and is re-grown for the next mating season." 

These animals are “so robust” in their sexual prowess, the authors say, that in one case a barnacle with two penises was still able to mate successfully.

“As barnacle biologists,” they write, “we understand and identify with Darwin’s excitement about barnacle reproduction and look forward to new knowledge generated through the modern-day comparative approach that has yielded so many new insights.”

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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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Big Questions
Why Do Dogs Love to Dig?
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Dog owners with green thumbs beware: It's likely just a matter of time before Fido turns your azalea bed into a graveyard of forgotten chew toys. When dogs aren't digging up your prized garden, they can be found digging elsewhere in your yard, at the beach, and even between your couch cushions at home. But what exactly is behind your dog's drive to turn every soft surface he or she sees into an excavation site?

According to Dr. Emma Grigg, an animal behaviorist and co-author of The Science Behind a Happy Dog, this behavior is completely normal. "When people say 'why do dogs dig,' the first thing that always comes to mind is 'well, because they're dogs,'" she tells Mental Floss. The instinct first appeared in dogs' wolf ancestors, then it was amplified in certain breeds through artificial selection. That's why dogs that were bred to hunt rodents, like beagles and terriers, are especially compelled to dig in places where such animals might make their homes.

But this tendency isn't limited to just a few specific breeds. No matter their original roles, dogs of all breeds have been known to kick up some dirt on occasion. Beyond predatory urges, Dr. Grigg says there are two main reasons a dog may want to dig. The first is to cool off on a hot day. When stuck on an open lawn with little to no shade, unearthing a fresh layer of dirt untouched by the sun is a quick way to beat the heat.

The second reason is to stash away goodies. Imagine your dog gets bored with chewing his favorite bone but knows he wants to come back for it later. Instead of leaving it out in the open where anyone can snatch it up, he decides to bury it in a secret place where only he'll be able to find it. Whether or not he'll actually go back for it is a different story. "There's a disconnect with modern dogs: They know the burying part but they don't always know to dig it up," Dr. Grigg says.

Because digging is part of a dog's DNA, punishing your pet for doing so isn't super effective. But that doesn't mean you should stand idly by as your yard gets turned inside-out. When faced with this behavior in your own dog, one option is to redirect it. This can mean allowing him to dig in a designated corner of the yard while keeping other parts off-limits, or setting up a raised flowerbed or sandbox especially to satisfy that urge. "You can get him interested in the area by burying a couple bones or some interesting things in there for him to dig," Dr. Grigg says. "I like the idea of buried treasure."

If your dog's motive for digging is more destructive than practical, he may have an energy problem. Dogs require a certain amount of stimulation each day, and when their humans don't provide it for them they find their own ways to occupy themselves. Sometimes it's by chewing up shoes, toppling trash cans, or digging ditches the perfect size for twisting ankles. Fortunately, this is nothing more walks and playtime can't improve.

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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