10 Ginormous Facts About Coconut Crabs

Janos/iStock via Getty Images
Janos/iStock via Getty Images

They're huge and antisocial. They will steal your silverware and can rip apart whole coconuts with their claws. Grab a piña colada and enjoy these 10 ginormous facts about the amazing coconut crab.

1. Coconut crabs are colossal.

Native to islands in the Indian and southern Pacific oceans, are truly humongous. They can weigh 9 pounds and measure 3 feet from leg to leg. Coconut crabs are the largest land-living arthropods—the phylum of joint-legged creatures that includes crabs, insects, spiders, and scorpions. Even Charles Darwin was stunned by their “monstrous size.”

But be aware: Occasionally, a viral photo circulates that exaggerates the coconut crab’s size. As biologist Michael Bok explains, the coconut crab in that infamous photo is normal sized, but the trash can is unusually small.

2. Coconut crabs are actually hermit crabs.

Coconut crab
Sandwich, Flickr // CC BY-NC-ND 2.0

Where does such a bizarre animal fit in the animal kingdom? Are they lobsters? Tarantulas? Space aliens? In fact, Birgus latro is a kind of hermit crab.

You may have seen smaller hermit crabs on a trip to the beach—or for sale at a pet shop. They take shelter inside abandoned snail shells, carrying them around as portable homes. But if coconut crabs are hermit crabs, then why don’t they live in shells? Well, they do—when they’re young and still small.

3. Coconut crabs quickly outgrow their borrowed shells.

Like other crabs, hatchling coconut crabs begin their lives floating freely at sea. After about a month of eating and growing, they find a snail shell and move in. The little coconut crabs carry this mobile home as they begin to transition to a land-based life.

A seashell is a nice, protected place to live, but it has its drawbacks [PDF]. As a crab gets bigger, its shell gets tighter—like an old pair of shoes on a kid who’s growing fast. The crab needs to find a bigger shell and make a quick switch. And that larger home will be heavier to tote around.

So, after a year or so of inhabiting shells, the coconut crab makes a major lifestyle change. It crawls out and hardens the parts of its body that were once protected by the shell by regrowing layers of calcium-based tissues, a process called recalcification. Without its old home, it’s free of size constraints. Now, unlike other hermit crabs, it can become enormous.

4. Coconut crabs eat coconuts, of course ...

This might seem obvious from the coconut crab’s name. But if you’ve ever tried to crack open a coconut, you know that it’s a steep challenge. In fact, a lengthy scientific debate once raged about whether coconut crabs were really able to open the fruit. It turns out that they’re up to the challenge—but they don’t just pop open their prize and dig in.

Breaking into a coconut is a mighty ordeal even if you’re a heavily armored crustacean the size of a small dog. Coconut crabs first use their claws to scrape away the fibrous coating. This can take hours or days. Finally, they stab into the fruit at a weak point and rip it open.

This diet helps coconut crabs grow large: those with access to coconuts may be twice as massive as those without. But eating the fruit isn’t essential for their survival. So what other items do the largest land-living arthropods shove into their maw?

5. ... but they also eat dead animals, their own body parts, and each other.

As well as the occasional biscuit, as you can see in the video above. (Note: Do not feed biscuits to coconut crabs.) A coconut crab’s diet may include other tropical fruits, fallen plant material, dead and decaying animals, rats, and other crab species. They’ll even eat members of their own kind. In fact, biologist Mark Laidre says they only relatively recently evolved to eat coconuts—a skill unique to modern coconut crabs—which helps them to eat each other less.

They also eat their own discarded body parts. As coconut crabs grow, they periodically molt their tough outer layer (the exoskeleton) and grow a new one. Once they’re done molting, which takes about a month, they gobble up their own exoskeleton.

6. Coconut crabs have an amazing sense of smell ...

Coconut crabs often forage at night. How do they find food when they’re wandering around in the dark? They sniff it out. These animals have a strong, highly efficient [PDF] sense of smell. In fact, a large portion of their brain is devoted to detecting odors.

7. ... which might explain why they're thieves.

Coconut crabs are also known as robber crabs because they snatch silverware and other objects and carry them away. Some people have even advanced the gruesome theory that Amelia Earhart’s remains are missing because coconut crabs hauled them down into their burrows. The thievery might be tied to that incredible sense of smell. Coconut crabs ignore objects that have been washed clean of scents, suggesting that they may only abscond with things that carry a faint whiff of food.

8. Coconut crabs are pretty antisocial.

Adult coconut crabs live alone in crevices or burrows. They aggressively guard their privacy; a crab entering another’s burrow risks becoming a meal.

But that’s not the end of their antisocial behavior. When coconut crabs emerge to feed, they keep their distance from each other. To maintain their personal space, they’ll announce their presence with ritualized claw waving. Laidre sought to find out if coconut crabs ever gathered together to interact (beyond mating or eating each other). The scientist tethered coconut crabs to one spot and watched to see if any others came to visit. They did not.

9. Coconut crabs carry their developing young under their abdomens.

After coconut crabs mate, females attach their eggs to special appendages and carry them under their abdomens. While the young develop inside the eggs, the females hold onto them, sticking near the edge of the sea so that they can periodically moisten the eggs.

But this care ends when the young are ready to hatch. The females release their hatchlings into the ocean waves. Now the tiny, floating babies must fend for themselves—and only a few will survive to return to land.

10. We need to learn a lot more about coconut crabs.

Coconut crab
Anne Sheppard, Wikimedia Commons // CC BY 3.0

Coconut crabs are little-studied creatures, and we need to know more about them—not just because they’re incredible and have a lot to tell us about biology, but also because we want to keep them around.

They may be huge and heavily armored, but they can be vulnerable. Coconut crabs take an extremely long time to grow big—they can live more than 40 years—and introduced predators such as rats can harm smaller, younger individuals or those in the process of shedding their exoskeletons (when their bodies are soft). Habitat loss has also caused local declines in some areas. The International Union for Conservation of Nature lists the coconut crab as data deficient: That is, we don’t know enough about its locations and populations. That’s why we need to study and learn more about these amazing, otherworldly critters.

5 Ways You Can Help the Jaguar Rescue Center Save Costa Rica’s Wildlife

A curious sloth says hello after members of the Jaguar Rescue Center reunited her with her baby.
A curious sloth says hello after members of the Jaguar Rescue Center reunited her with her baby.
Jaguar Rescue Center

In 2005, Catalonian primatologist Encar Garcia and her husband, Italian herpetologist Sandro Alviani, were living in southwestern Costa Rica when locals began to bring them injured animals in hopes that the two experts could save them. As word spread and more animals arrived, their property slowly transformed into a full-fledged rescue center. So they purchased the surrounding land and named their new organization the Jaguar Rescue Center (JRC), after one of their early rescues: a young, orphaned jaguar whose mother had been killed by farmers.

Today, the center covers nearly 5.5 acres of land near Puerto Viejo de Talamanca in Costa Rica’s Limón province. It can accommodate around 160 animals at a time, and is home to everything from spider monkeys to sea turtles (though, by law, staff members aren’t allowed to accept domesticated animals like cats and dogs).

While locals still bring injured and orphaned animals to the JRC, others are brought by tourists, the Ministry of Environment and Energy, the National Animal Health Service, and even the police, who confiscate animals that have been poached or illegally kept as pets.

howler monkey at jaguar rescue center
Skye, a young howler monkey who recovered from electrocution.
Jaguar Rescue Center

The rescues are often victims of road accidents, animal attacks, environmental destruction, human interaction, or electrocution from exposed power lines. After the animals are rehabilitated, they’re released into La Ceiba Natural Reserve, a human-free (except for JRC workers) part of the forest where they can safely reacclimate to living in the wild. The JRC has cameras installed in the area to monitor the animals after their release and make sure they’re finding enough food.

Unfortunately, not all the creatures brought to the JRC recover from their injuries—in 2019, for example, 311 of the 749 rescues died [PDF]—so JRC staff members and volunteers understand just how remarkable it is to watch an animal regain its health and be successfully returned to its natural environment.

“There are so many amazing things about working for the JRC, but I think we all can agree that seeing a rescued animal make it through rehabilitation and be released is the best and most rewarding part of the job,” Torey, a JRC tour guide, tells Mental Floss.

Some thought-to-be-orphaned sloths are even released right back into the arms of their mothers. After recording the cries of a baby sloth, JRC staff will take the sloth back to wherever it was first found, play the recording, and wait for the mother to recognize the cries and (slowly) climb down from her leafy abode to reunite with her child.

Despite its partnerships with government agencies, the JRC doesn’t receive government funding. Instead, it relies on public donations and revenue from its visitor services. Find out more about how you can help below.

1. Donate money.

You can make a one-time or monthly donation that will go toward food, medical care, and supplies for the animals, or you can donate specifically to the JRC’s “Shock Free Zone” program, which insulates power lines and transformers that run through forests to prevent them from electrocuting wildlife.

2. Donate items.

Check out the JRC’s Amazon wish list to see which items are most needed—and what they’ll be used for, too. Examples include Pampers diapers for baby monkeys, snake hooks for safely rescuing snakes, and cans of worms to feed birds, opossums, and bats.

One of the most important products on the list is powdered goat’s milk, which staff members use to feed orphans of many mammalian species at the JRC.

“It has the most universally digestible enzyme compared to other milk,” Torey says. “Unfortunately, we do not have sloth milk, monkey milk, etc. readily available for the baby animals.”

3. “Adopt” an animal.

diavolino, a margay at the jaguar rescue center
Diavolino, the Jaguar Rescue Center's "feisty little margay."
Jaguar Rescue Center

For $105, you can virtually “adopt” an animal at the JRC. Choices range from Diavolino, a “feisty little margay” rescued from the illegal pet trade, to Floqui, a whitish two-fingered sloth who was born with only one digit on each hand and foot.

4. Visit the Jaguar Rescue Center.

You can stay overnight at the JRC in one of its three visitor residences—La Ceiba House, Ilán Ilán House, or one of the Jaguar Inn bungalows—which offer a variety of amenities, restaurant service, and access to nearby beaches.

Whether or not you’re staying there, you can book a tour of the JRC, where you’ll get to explore the premises and even meet some of the animals. There are private, public, nighttime, and VIP tours, and you can find out more here.

5. Volunteer at the Jaguar Rescue Center.

If you’re looking for a more hands-on, potentially life-changing way to help Costa Rica’s wildlife, you can apply for the JRC’s four-week volunteer program or a position at La Ceiba Natural Reserve that lasts three to six months.

According to the website, JRC volunteers are housed in the Jaguar Inn and help with “a broad range of tasks, from doing the dishes and cleaning up after the animals ... to building and remodeling enclosures, or babysitting a new arrival to ease the stress of their new environment.”

La Ceiba volunteers, on the other hand, stay right on the reserve and do everything from monitoring captive and recently released animals to keeping the trails clear.

Find out more about becoming a volunteer here.

YouTube Star Coyote Peterson Brings 'Misunderstood' Animals to His New Animal Planet Series

Animal Planet
Animal Planet

As host of the popular YouTube series Brave Wilderness, Coyote Peterson is no stranger to going face-to-face with creatures many deem terrifying—think great white sharks and pit vipers—but that he says are simply "misunderstood."

Animals have always been a big part of Peterson's life, even before he made a career out of being stung and bitten by ferocious critters. The Ohio native studied video production and directing at Ohio State University, and then decided to combine his two passions—film and all things wild—to teach viewers about wildlife and the importance of conservation. His YouTube channel currently has more than 15 million subscribers.

Now Peterson is embarking on a new adventure with Animal Planet in the show Brave the Wild. He'll travel all over the world with wildlife biologist Mario Aldecoa and his crew, sharing creatures that aren't often in the spotlight and that viewers may find a little frightening. He recently chatted with Mental Floss about the importance of conservation, his thing for snapping turtles, and his close encounter with a jaguar and her three cubs.

You’ve said your love of animals started with snapping turtles. Can you talk about the first time you saw one and what about them fascinated you so much?

The first snapping turtle I caught was when I was only 8 years old. I was always fascinated with turtles, because at first glance they look prehistoric, almost dinosaur-like. Growing up in Ohio, I never got to see any "exotic" animals. My favorite thing to watch on TV was Steve Irwin. Watching him wrestle crocs is what inspired me to catch my first snapping turtle, the most dangerous animal Ohio has to offer.

Coyote Peterson with a gigantic snapping turtle
Animal Planet

In Brave the Wild, you introduce animals that are often feared or misunderstood. What's the importance in exposing viewers to these creatures?

One of my goals through this series was to inspire people to overcome their fears of these seemingly dangerous animals and learn to admire them from a safe distance. The more you understand these creatures, the less you are afraid of them. One of the messages I try to convey in every episode is the importance of conservation.

What’s the most "misunderstood" creature you've encountered?

The most misunderstood creature that comes to mind is the carpet shark, which we filmed in season one. As I always say, people’s biggest fears are the three S’s (sharks, snakes and spiders). The carpet shark is found off the coast of Australia. They only bite humans in the case of mistaken identity. To some of these sharks a person’s foot might look like a fish. Any time you enter a new environment you need to be aware of what you need to look for, not only to keep yourself safe, but the animal as well.

What goes into preparing for each encounter to make sure you and the animals come out alive?

With any new expedition, you need to come into the environment knowing exactly what to expect. When encountering a new animal, I try to stay as calm as I can and have no hesitation. If I stay calm, the animal stays calm, [and] I'm creating a safer interaction for myself. I use different tactics when I encounter different animals. It also depends on whether the environment is land or in water.

How do you keep your composure on camera when you're in a potentially dangerous situation?

Any situation I find myself in, I look at it as my job. For example, I would be afraid operating a crane, because that is something I don't do. If it's part of your job, it's something that you get used to. When I do my job, I make sure I'm focused and never hesitate. Before I encounter any animal, I know what I'm going to say to the camera. I say that, for the best show, we always need to have the camera rolling so the audience can see what is happening.

Coyote Peterson with a kangaroo
Animal Planet

You were in Australia filming Brave the Wild during bushfire season. What was that like?

Visiting Australia was one of the best experiences I had filming the show. Australia is a fascinating country that has so many unique environments. We spent over 50 days in Australia and encountered more than 35 different species. We were there right before all these devastating fires started, and we got to witness the severity of the drought and all the different animals it impacted.

What was your favorite animal encounter in upcoming series?

Each encounter I have in the wild is special. I would have to say that the most exciting moment for me was when we were filming in Brazil and I saw a jaguar and three of her cubs up close. Not only did I get to see this in real life, but my amazing team was able to capture this special moment on tape. It is just so amazing seeing these animals survive and thrive in the wild while dealing with not only the dangers of the wild but human encroachment as well. Hands down, this was my favorite episode that we got to film.

Catch new episodes of Brave the Wild on Animal Planet, Sundays at 9 p.m. ET/PT.

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