Baby Eels Migrate by Following Magnetic Fields

Alessandro Cresci
Alessandro Cresci

Baby eels have joined the ever-growing club of animals that live their lives along magnetic lines. Researchers described these findings in the journal Scientific Advances.

Our planet and its inhabitants are shaped and impelled by invisible forces. Studies have found that foxes hunt and deer flee along north-south lines. Pigs and wild boars orient their nests to face the same way. Lobsters, butterflies, and whales all follow their internal compasses along magnetic lines. Adult European eels, too. But we weren’t really sure about their babies.

Grown-up European eels lay their many eggs in the Sargasso Sea. The eggs hatch into helpless larvae, which bob along in Atlantic currents. As the currents approach the continent, the babies transform again, this time into translucent miniature versions of their parents. These glass eels make their way into the coasts. From there, they swim inland to freshwater and bum around Europe and North Africa for five to 20 years. Finally, as adults, they head back to the sea to start the whole cycle all over again. It's one of the longest migrations in the animal kingdom, the researchers say.

Adult European eel traveling over icy ground on its migration route
Adult European eels are tough and can migrate short distances over land.
Caroline Durif

It’s an impressive feat for the little noodles, and scientists wondered how they pull it off. To find out, researchers scooped up a group of newly arrived baby eels on the coast of Norway. They put the eels in a large chamber inside a fjord and let them swim there for a full tidal phase, watching how the eels positioned their bodies and how they swam.

Next, they brought the eels into the lab and repeated the tide-long observation process.

Unsurprisingly, the little tykes knew exactly what they were doing. They consistently turned their bodies to run parallel with magnetic lines, but the direction of those lines varied depending on the phase of the tides. When the tide went out to sea, the majority of eels swam southward, whether in the fjord or in the lab.

These findings are as fascinating as they are vital, as, for all its ingenuity, the European eel is critically endangered. Understanding this animal’s extraordinary life cycle could help conservationists find ways to protect it better in the future.

Why Do Dogs Lick?

iStock/MichaelSvoboda
iStock/MichaelSvoboda

​One of the more slightly annoying things our dogs do (or most adorable, depending on who you ask) involves their tongue obsessively licking every crevice of every spot possible in pretty much the whole world. From our faces to our furniture to themselves, some dogs are absolutely in love with licking anything and everything. Although it can be cute at first, it quickly gets pretty gross. So why do they do it?

According to ​Vetstreet, your pup's incessant licking is mostly their way of trying to show affection. When we pick up our dogs or give them attention, chances are we kiss or pat their heads, along with petting their fur. Their way to show love back to us is by licking.

However, there are other reasons your dog might be obsessively licking—including as a way to get attention. Licking can be a learned behavior for dogs, as they see that when they lick their owner, they get more attention. The behavior can seem like something humans want which, to an extent, it is.

Licking is also a sensory tool, so if your dog is licking random objects or areas of your home, they're probably just exploring. It's easier to get a feel for their surroundings if they can taste everything. But licking objects like your rug or furniture can also be indicative of anxiety or boredom (which can often lead to destructive behavior), and a recent study linked excessive licking of surfaces to certain gastrointestinal disorders.

Another reason for licking is your dog wanting to clean themselves and/or spots around them. They've seen it since they were born; animals lick things ritualistically for cleaning and care. If your dog seems to be obsessed with licking themselves or one particular thing, they probably are. (Yes, dogs can have OCD, too.)

As Vetstreet points out, "excessive" dog licking often only seems excessive to the dog's owner, not the pooch itself. But if it's bothersome enough to you, a trainer can often help curb your dog's enthusiasm for giving wet, sloppy kisses. And while strange behavior is not rare for pets, if your dog's licking seems odd or in any way concerning, there's no harm in taking your pet to the vet to check it out—even if it's just for peace of mind.

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

5 Holiday Foods That Are Dangerous to Pets

iStock/svetikd
iStock/svetikd

One of the best parts of the holiday season is the menu of indulgent food and drinks that comes along with it. But while you enjoy that cup of spiked hot cocoa, you’ve got to be careful your dog or cat doesn’t nab a lick. Here are five holiday treats that are dangerous for your pets, according to Vetstreet.

1. COFFEE

Any coffee lover will agree that there’s nothing quite like an after-dinner cup of joe on a cold night. But pups, kitties, and other pets will have to sit this tradition out. Caffeine can prompt seizures and abnormal heart rhythms in pets, and can sometimes be fatal. Other caffeinated drinks, such as soda or tea, should also be kept away from your four-legged family members.

2. BREAD DOUGH

We know the threat that bread dough poses to the appearance of our thighs, but it’s much more dangerous to our furry little friends. Holiday bakers have to be careful of unbaked bread dough as it can expand in animal stomachs if ingested. In some dogs, the stomach can twist and cut off the blood supply, in which case the pup would need emergency surgery.

3. CHOCOLATE

Cat and dog in Santa hats chowing down on plates of food
iStock/TatyanaGl

A little chocolate never hurt anybody, right? Wrong. The sweet treat can cause seizures and even be fatal to our pets. Darker chocolate, such as the baker’s chocolate we love to put in our holiday cookies, is more toxic to our pets than milk or white chocolate. The toxic ingredients include caffeine and theobromine, a chemical found in the cacao plant.

4. MACADAMIA NUTS

Macadamia nuts, which are a common ingredient in holiday cookies and often put out to munch on as an appetizer, can be toxic to dogs. While poisoning might not always be easy to detect in a pet, clinical warning signs include depression, weakness, vomiting, tremors, joint stiffness, and lack of coordination.

5. ALCOHOL

Think back to when you first started drinking and how much less alcohol it took to get you tipsy, because you likely weighed less than you do now. Well, your pet probably weighs a lot less than you did, even back then, meaning it takes much less alcohol to make them dangerously sick. Keep those wine glasses far out of reach of your pets in order to avoid any issues. Well, maybe not any issue: We can’t promise that this will stop you from getting embarrassingly drunk at a holiday party this year.

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