Slowness in the animal kingdom is the virtue by which energy can be conserved. It’s the way to survive in cold environments or places where there isn’t much oxygen. It’s sometimes an animal can go unnoticed, or, in the case of animals in cars, a great way to draw attention to oneself.
The slowest animals on Earth don’t go anywhere at all. They’re entirely fixed in place, like barnacles or tube worms.
We don’t want to populate a whole list of barnacles, so we’ll ignore these.
The next-slowest burrow into the ground and stay there, like many molluscs and worms. We don’t want to populate a list of worms, either, so we’ll ignore these, too.
Across the vast branches of the animal kingdom, slowness has benefitted animals of all kinds, so while it’s possible to arbitrarily rank these animals by speed, it’s more interesting to look at why, among their kind, they’re so slow.
So, here’s a list of ten of the slowest animals, by type.
10. Slowest Reef Creature: Starfish
Starfish have so many limbs there’s really no excuse for them moving so slowly. Of all the animals on this list, they’re the only ones with radial symmetry, representing a phylum of very strange animals called the Echinoderms.
Starfish symmetry surrounds a central point, rather than a bilateral line, like most animals we’re familiar with. That means they can have anywhere from five to 50 arms, radiating from their mouth.
And still, they’re remarkably slow animals. Despite this, they are constantly on the move, using thousands of little sticky protrusions to carry themselves around and, amazingly, hunt other animals.
Starfish feed on the only animals slower than they are: the sponges and bivalves that don’t really move at all. To see what they’re truly capable of, you need to speed up the footage quite a lot. And when you do, their ecology immediately comes to life.
9. Slowest Primate: Slow Loris
I’m sure we all personally know a contender for this one, but the chances are, the Slow Loris has even them beat.
These nocturnal primates are known not only for their deliberate movements but also for their low breeding rates. Everything the slow loris does is frustratingly nonurgent, but they don’t need to move all that fast because they’re one of the only venomous mammals.
They have a secretion from glands under their arms that contains a powerful irritant. When licked, it coats the mouth of the loris and can be injected into potential predators or unsuspecting vloggers with disastrous consequences.
This chemical has been shown to put off animals like the clouded leopard and binturong and has even been attributed to one human death.
8. Slowest Bony Fish: Dwarf Seahorse
Seahorses are funny little things, but while they don’t look it, they are in fact, regular bony fish like the trout and salmon of the world.
Still, they don’t swim about using the same mechanisms as most of their class, instead relying on gentle movements and a prehensile tail to move relatively little and stay hidden instead.
So it stands to reason that the smallest of them would be some of the slowest. These little fish move around 1.5 meters every hour, the slowest rate of any such fish recorded.
Being a tiny predator as well as a common prey item, they have a key role in their ecosystem as both population control and food supply, respectively. Like chameleons, they use their slow movement as a way of staying camouflaged among leafy hiding places. 1
7. Slowest Mollusks: Slugs & Snails
Terrestrial gastropods are well known for being slow, and like the loris, they’ve developed some gross deterrents in place of being swift underfoot.
Both slugs and snails move around by contracting and relaxing their entire muscular body from the tail to the head. These waves interact with their 0.04 mm-thick layer of sticky mucous and create a propulsion that is still not fully understood.
Interestingly, this is a hugely inefficient way of getting around. In sea snails especially, it’s thought that mucous pushing is twelve times as energy-intensive as a mouse running, one hundred times more so than a fish swimming, and might be the most costly form of locomotion in the animal kingdom.
The mucous that allows gastropods to move is astounding in itself. It’s created by special granules which, on contact with water, burst and swell up to 800 times their original size.
This mucous protects from physical and chemical threats, but overcoming its stickiness to move the gastropod around takes a huge percentage of the energy the animal gains as food, and that is why they can only get about at a snail’s pace.
For example, a banana slug’s most impressive pace rarely exceeds 300 meters in an hour.
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6. Slowest Reptile: Tortoise
Another fabled slowcoach is the tortoise. There are two main reasons for this: the first is their poor diet. Slow-motion allows them to not overspend their resources, but their heavy armour plating creates certain physical restraints, too.
Interestingly, unlike snails and slugs, tortoises are highly economical in their walking, and the cost of transport in terms of energy expenditure is much lower, relative to their mass than most animals.
5. Slowest Insect: Stick Insect
If we were being pedantic here, the entry would likely be the 17-year cicada, whose lengthy development stage has them stuck in the ground for almost two decades before emerging and spending their last month just a few meters away.
But for the slowest, regularly-moving insect we have to look to the stick insects, for whom slowness is a feature, not a bug.
Stick insects are so named because they mimic sticks and leaves in the way that they look. But stick mimicry hits a limitation when it comes to locomotion. Sticks aren’t known to be highly migratory, but the insects do need to get about, so they compromise.
Moving exceptionally slowly, and with an impressive sway that disguises their locomotion as a fluttering leaf, they can find one another on branches without giving the game away to would-be predators. 3
4. Slowest Flying Bird: American Woodcock
Sometimes, it’s even possible to be slow on the wing. Woodcocks are American birds who quite clearly prefer to be on the ground. While they can fly, and fly fairly well, they are also the owner of the record slowest flight, at 8 km/h (5mph).
They fly at low altitudes and at night, suggesting that they’re a bit embarrassed by it. They’re much more comfortable pottering about in the undergrowth, eating insects and worms. However, when it’s time to mate, they will engage in courtship rituals called Skylarking, which is basically trying to show how not rubbish they are at flight.
They’ve also got some serious groove. While clearly not built to fly, they can dance if they want to, and they’ll leave your friends behind. The reason for this awesome wiggle is still not entirely clear.
3. Slowest Shark: Greenland Shark
Greenland is known for being cold. And spending your life submerged in arctic waters is no doubt going to slow you down, especially if you’re a big fish with a low body temperature.
Despite being able to catch seals, somehow, Greenland sharks spend their time cruising at less than 1 km/h. Their Latin name translates to “sleepy smallheads”.
They’re so slow that they almost all have a species of parasitic crustacean living on their eyeballs, which would presumably be too slow to catch a shark at normal speeds.
This low speed to life is a product of the cold, year-round icy temperatures, but it also reduces energy expenditure significantly, and this shark grows to ripe old ages. 4
2. Slowest Mammal: Three-toed Sloth
The three-toed sloth puts even the slow loris to shame. This is a mammal that moves so slowly, that moss can catch up with it.
Its characteristic green coat is an algae layer that builds up on the sloth’s fur and creates a unique ecosystem inside which several species can be found, endemic to the sloth itself.
Unlike the loris, the sloth has no chemical defences (though they are quite smelly), and instead relies on a powerful bite and some long, stabby claws to deter its enemies.
Sloths sleep up to 20 hours a day, so don’t even move fast on average, and even by sloth standards, three-toed sloths have a low body temperature. Their lows are roughly 7 degrees colder than most homeothermic mammals, saving energy on thermoregulation so they can sleep more and eat less. 5
1. Slowest Ocean Giant: Ocean Sunfish
The most massive bony fish in the world is also one of the slowest. This animal weighs up to 1.4 tons, but until recently researchers thought it was entirely at the mercy of the ocean currents.
As it happens, it can swim, but barely.
The heaviest bony fish in the ocean tops out at around 3 km/h at full sprint, and relies primarily on drifting to get from one place to the other.
This slow pace of life attracts over 40 different parasites, and the fish have been seen basking at the surface of the ocean looking mostly dead, allowing birds to pick at them. 6
Final thoughts
That completes our list of the slowest animals on the planet. Speed in the animal kingdom is often an advantage, but it’s costly.
Sometimes, slowing things down is the best path to success. Whether it’s to better hide, better sneak, or simply to conserve energy, slow movement is common in nature, where it’s needed the most.
Other times, it’s a product of another adaptation, such as using thick and sticky mucous for protection. In these cases, the gain is always greater than the loss, otherwise it wouldn’t have become the norm.
Fact Sources & References
- “DWARF SEAHORSE“, Center for Biological Diversity.
- Heller, J. (2015), “What Is a Snail?“, Sea Snails.
- “Walking Sticks“, The National Wildlife Federation.
- Allison Guy (2016, “Maligned as Lazy and Toxic, Greenland Sharks Are Smarter than You Think“, Oceana.
- “Three-Toed Sloths“, National Geographic.
- “Cause of the Month: Ocean Sunfish“, 4 Ocean.