How lazy is too lazy?
It’s easy to feel guilty for not always going the extra mile in our productivity-obsessed society. But scientists have found that a penchant for laziness may be wired into our biology: Researchers from the University of British Columbia observed that our brains must deliberately work harder to choose exercise over sedentary activities, according to a study published in Neuropsychologia in 2018.
Fortunately, even the most committed couch potato pales in comparison to some of the feats of inaction taken by the animal kingdom. Enjoy our brief foray into the world of truly work-averse critters — and perhaps feel just a bit prouder of your own achievements.
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We’ll start with the more familiar — and charismatic — animals: lions. You wouldn’t know from looking at the muscular physique of the big cats, but they’re notorious for sleeping on the job. Females, who often do more of the hunting and babysitting, get around 18 hours of shuteye a day, while males usually doze off for more than 20. A full day’s rest is usually in order after a big kill.
Sure, lions may have to duke it out with some of Africa’s fastest and toughest game, like gazelles and water buffalo, but they also know how to kick their feet (err, paws) up when they need to recharge.
Of course, lions don’t hold a candle to what is arguably the best-known lazy mammal: the sloth. Sloths have earned their reputation for good reason. They move the slowest out of any mammal; on average, sloths barely travel over a hundred feet a day, less than half a football field.
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Thanks to their low metabolic rate, which allows them to expend less energy, sloths can remain hanging from branches, motionless, for hours on end, allowing a camouflaging coat of algae to grow on their bodies. Sloths have even been hypothesized to “garden” themselves, scraping the slimy surface from their bodies and consuming it for a quick snack.
For most of a sloth’s nutritional needs, a paltry diet of leaves will have to make do. Still, if you thought all that extra fiber would keep bowel movements regular, you’d be sorely mistaken. For instance, the three toed sloth’s digestive system is so lethargic that the animals only need to descend from their trees once a week for their excretory endeavors.
Of course, lions and sloths are mammals, like us, which are known for being the least lazy among animals. All mammals are warm-blooded and expend great amounts of energy to keep their insides toasty, and consistently so. In fact, around half of the calories we consume just go toward maintaining our body temperature.
3. Greenland Sharks
(Credit: Hemming1952/CC-By-4.0/Wikimedia Commons)
Let’s leave the world of the mammals and look toward the cold-blooded champions of inaction. To this end, few outclass the Greenland shark (Somniosus microcephalus), typically found in the Arctic.
Living at depths of more than 7,000 feet (or about twice the height of the Burj Khalifa, the world’s tallest building), where the water pressure can crush a human lung into a Coke can, the sharks drift along at the blisteringly slow pace of 0.6 miles per hour. These animals don’t need to move very fast, since they aren’t picky eaters and will try any bit of flesh, rotting or not, that arrives their way.
The cold polar waters seem to slow down time for their inhabitants, as well. Cooler temperatures reduce the rate of metabolism, allowing some animals to reach larger sizes due to their exceptionally long lifespans. The examples are numerous, from giant isopods that resemble overgrown pill bugs to the elusive colossal squid. The Greenland shark is no exception, living over 400 years — longer than any other vertebrate.
Of course, these lives aren’t always the most pleasant, as the sharks are consistently afflicted by a parasite called Ommatokoita elongata. This copepod, a type of crustacean, grows on the host’s eyes and consumes corneal tissue, rendering Greenland sharks virtually blind. Surprisingly, the sharks don’t seem to mind their gruesome fate too much, perfectly adapted to smell and bump their way through their submarine world.
4. Deep-Sea Anglerfish
A female deep-sea anglerfish (Edridolychnus schmidti) with two parasitic males along for the ride, who fertilize the female’s eggs. (Credit: Neil Bromhall/Shutterstock)
But while Greenland sharks swim around, albeit slowly, some aquatic animals have given up on such pursuits entirely. Enter the male anglerfish. While there are over 300 species of anglerfish, the deep-sea varieties dwell thousands of feet below the surface, where light scarcely penetrates, making it rather challenging to locate food…or mates.
To solve both problems, the female anglerfish must use a glowing lure to draw in meals and lovers. The former is dispatched with a set of fearsome teeth and oversized jaws. The latter bites the female on its belly and never lets go. How clingy!
Some species of male anglerfish are significantly smaller than their egg-laying counterparts, and simply stay attached for the ride. After all, it’s easy to lose your muse in the darkness.
To ensure that nothing, even skin, gets between the couple, the bodies fuse bloodstreams, and the male’s fishy form slowly withers away. It loses eyes, muscles, a digestive system, everything — that is, except for its sperm-producing testes. Ever indiscriminate, the female may carry several such appendages on her body, mixing and matching genetics as it continually spawns their progeny.
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Of course, there’s one question raised by the anglerfish: why move, ever? Many of its fellow aquatic denizens have taken note, settling themselves firmly on the seabed — permanently. From colorful giant clams to barnacles, there’s no shortage of creatures that have taken inspiration from plants and simply stopped moving.
Instead of actively hunting for food, these (mostly) immobile animals simply let it come to them. Deploying elaborate appendages, they filter the water for tiny plankton and bits of detritus. Not requiring any of the meddlesome body parts needed for locomotion, many have lost sensory organs and other such bodily systems, much like the male anglerfish.
Some have gone a step further, and never even evolved a heart. These are the anthozoans, a group of aquatic animals that includes sea anemones and corals. Closely related to jellyfish, oxygen simply diffuses into their bloodless tissues, which are mostly water. Food and waste, meanwhile, enter and exit the same opening. It appears developing a through-gut like ours is just too bothersome.
6. Sea Sponges
But it is the humble sponge who has outclassed all by losing all forms of muscles, a hallmark of motility in animals. Instead, they beat microscopic hairs called flagella to suck water into their hole-ridden bodies, the same mechanism that sperm use to move around. Without definite shape or symmetry, a sponge can be ground up in a blender and slowly reassemble itself thereafter, so long as enough cells are left intact.
In addition to being the simplest animals, sponges have also outsourced much of their labor to a motley crew of microbes that live symbiotically inside of their bodies. In exchange for shelter, the diverse cadre of bacteria, fungi, and others perform a range of functions, from boosting their host’s immune system to filtering out harmful chemicals like an outsourced kidney. Some sponges use in-house algae to generate sugars from photosynthesis.
Some may call this strategy lazy, but others might deem it efficient, like relying on your neighbors for a helping hand. Perhaps there’s a lesson here for the rest of us.