Hermit Crabs

Alex Re (00:01): Hello, welcome to On Wildlife. I'm your host Alex Re. On this podcast, we bring the wild to you. We take you on a journey into the life of a different animal every week, and I guarantee you you're going to come out of here knowing more about your favorite animal than you did before. This week we're taking you back to the beach to look at another marine animal. These animals like to make their homes out of shells. You may have picked up while looking through the sand, but there's a lot more to them than meets the eye, so try not to get pinched because we're going to be talking about a family of crazy crustaceans, hermit crabs.

(00:55): The hermit crab is part of the super family Roia. This family is comprised of 10 legged crustaceans that have gained adaptations which allow them to occupy empty shells. There are 800 species of hermit crabs living in coastal waters all over the world, and almost all 800 species live in the ocean. But you may be more familiar with the few semi terrestrial species known as land hermit crabs. These species are the ones that people usually picture when they think of hermit crabs because they're known to be kept as pets, but they're really in the minority as most of them are fully aquatic. Apart from the terrestrial and saltwater hermit crabs, a single freshwater species exists too. Its scientific name and it's found on the South Pacific island of Vanuatu. There are a lot of really cool and unique hermit crab species around the world. The coconut crab, also called the robber crab, can weigh almost 10 pounds, is three feet long and has been known to eat birds.

(02:03): They can even break coconuts open with their claws, which is how they got their name. The green-eyed hermit crab doesn't use a shell at all. It has a symbiotic relationship with sea anem. To help with this, they anchor themselves onto the hermit crab and are glued together by sand, and the sea anemone shell actually grows as the hermit crab grows. This is beneficial for both organisms because the anemone gets a place to anchor itself to and the hermit crab gets protection. And because of this, we would call it a mutualistic relationship. As I mentioned before, hermit crabs are crustaceans, which means that they have a segmented body, a tough outer shell, jointed limbs, and two pairs of antenna. Some other crustaceans are lobsters, crabs and shrimp. They have a long pair of antenna and a short pair. The longer pair is used for feeling around their environment while the shorter pair helps them smell and taste a hermit.

(03:03): Crab's eyes are located on top of these long stalks that stick out of their head. This is beneficial for them because it helps them see more of their surroundings and hermit crabs aren't even true crabs, even though they're called hermit crabs, they're actually more closely related to lobsters. Their exoskeleton doesn't cover their whole body. It only covers the front of their body and they can't grow their own shells and they actually have soft tails, but the tails are protected by the shells that they find in their environment. In order to keep the shell on their body, they have a hook on their tail, which is used to curl up and it acts as an anchor point. Their tail has to twist in order to wrap around the curves of the shell, and I urge you to look at a picture of a hermit crab without its shell on.

(03:51): It's like looking at a completely different animal. Hermit crabs are named after this behavior of taking shells and making them into a home. But despite being called hermits, they actually like to live in large social groups and they very rarely steal shells that another crab is already using as a home. Instead, they like to search their environment for empty shells. These shells can come from animals that are able to make their own like snails and hermit crabs vary in size because there are so many different species. Some can be as small as a half an inch and some grow up to 11 inches. Both aquatic and terrestrial hermit crabs need to breathe using gills. Terrestrial hermit crabs need to live in moist environments so that their gills are getting the oxygen that they need from the water in the air, and we're going to start talking about what they eat right after the break. This week I want to give a shout out to Kate from North Carolina. Her favorite animal is an elephant. Elephants have more muscles in their trunks than we have in our entire body. If you want me to give you a shout out on the podcast, send an email to on wildlife dot podcast@gmail.com telling me your first name, where you're from, and your favorite animal.

(05:28): Now back to the episode. Hermit crabs are extremely opportunistic consumers and will eat just about anything they can find. So we could classify them as omnivores who scavenge for most of their food. They eat muscles, clams, dead organisms, and some types of algae. They could also eat smaller fish and shrimp. While those in captivity often eat vegetables and fish food, despite not being picky eaters, hermit crabs will usually stay away from live prey. Younger hermit crabs in their larval stage mainly rely on plankton for their food. Most hermit crabs are nocturnal, so they'll forge for food at night. There are a lot of animals that would eat a hermit crab, so going out in the dark is much safer and they use all five of their senses in order to find food. They have hundreds of tiny hairs on the smaller pair of antenna. These hairs are called este tasks and they enable them to pick up scents from their environment or taste the sand for any semblance of food.

(06:31): Coconut crabs can use these hairs to smell coconuts from really far away and other hermit crabs are great at smelling dead and decomposing organisms. A large part of a hermit crab's brain is dedicated to process smells that they find and their brains are so small that you would have a hard time seeing one without some sort of magnification. And we already talked about how they have their eyes on stalks and because of this they have complete 360 degree vision. They can also see colors and differentiate between them pretty well, but their vision is limited when it comes to seeing shapes. Hermit crabs can also hear a range of medium to low frequencies, but it's not used as much during their search for food. Their sense of hearing is really helpful in knowing if any predators are around. If a hermit crab finds another individual with food, it will go towards it to share the meal and when they eat, they use their claws to break apart larger pieces of food making it easier to consume.

(07:31): The outer parts of their mouths are called maxillipeds, which help to move the food into the mouth. In some species, hermit crabs will eat their own kind by ripping them out of their shells, or they'll dig up molting crabs and eat them when they're at their most vulnerable. The mating habits and rituals of hermit crabs are different depending on the species. One example is the Caribbean hermit crab. It usually lives in wetlands or marshes, but they all collectively move to the seashore. When it comes time to m mate, the mating season takes place in summer for some species, fall for others, and still some can mate all year round. Hermit crabs always mate in seawater though, even if they live on land. The salty seawater provides the best conditions for their larvae to survive, and this is because the temperature is usually optimal and there's a lot of food.

(08:24): Some studies have found that hermit crabs mate, based on their size, larger females will mate with larger males because the females are able to hold more eggs. After mating, the eggs are fertilized and the female holds the eggs for about a month. Once they mature, the females release them into the open ocean with the help of their GI appendages that push the eggs out. Hermit crabs can lay between a couple thousand and 50,000 eggs at a time. They lay so many eggs because very few of them will survive into adulthood. As soon as the eggs are released, they hatch and the larvae begin their journey into the sea. Once the eggs hatch, those larvae are now completely on their own and there are four stages of life for a hermit crab. They begin their lives as zoa, which are small and free swimming. This is the larval stage.

(09:17): After molting, a few times they become mega lopa. They're still small, but now they look more like crabs. Molting basically happens when hermit crabs outgrow their exoskeleton, so they have to shed it off and grow A new one, and I'll elaborate more on this process later on in the episode. Very few mega lopa live past the first few hours after they molt because those who are stronger will often eat the others to gain even more strength. Any mega lopa that survive will dig holes in the sand to molt and become juveniles. Juveniles look a little closer to hermit crabs you see in the wild, but they're much smaller and are just beginning to look for shells. If the juveniles survive, they'll molt and grow into adults. Adults then join other individuals in large groups of hermit crabs and will move into their more permanent shells.

(10:11): Hermit crabs stay in the ocean until they reach adulthood. Regardless of if they're terrestrial or aquatic, they need to stay in the water until they grow their exoskeleton, and the water also keeps their gills and stomach running efficiently. Because of this meticulous process, they're extremely hard to breed in captivity, but if they do breed, it's generally best for them to breed. During the summer months, hermit crabs are able to reproduce for their whole life, which can span decades or can be over in a few years. Most live between one and 10 years with some living over 30 years. The longest living hermit crabs are called coin beta breman, and they can live for up to 70 years. So you can already tell that hermit crabs are amazing creatures, but I've got plenty more stuff to talk about right after the break time for our trivia question, what is the largest terrestrial animal to ever roam the earth? The answer is a titanosaur species called dread natus. It could be 85 feet tall and weigh 65 tons. That's the weight of over 13 African elephants.

(11:50): Okay, welcome back. Hermit crabs are very social animals and they like to form groups also called clusters. This happens once they reach their adult stage and start to find their larger shells, and these clusters can have over 100 individuals in them. Scientists believe that hermit crab clusters are more likely to form near sites that have more shell availability because they'll have more options to choose from. These clusters can also benefit hermit crabs by staving off attacks from predators because there's safety in numbers. Basically, if a predator is choosing from a group of 10 hermit crabs to eat, or from a group of a hundred, you're less likely to be the one that gets eaten in the group of a hundred. This allows them to spend less time hiding in their shells and more time foraging for food. There's also a sort of hierarchy among hermit crabs, both in the wild and in captivity.

(12:48): The dominant individual gets to be the first one to eat, breed, and pick their next shell to move into. Each individual has a rank in this hierarchy, so the further down you are in the pecking order, the less choices you have. Newcomers may get tested once they join a group to see where they fall in this social hierarchy through antenna fights. Hermit crabs can also push or flick other individuals to establish dominance and get them to stay away from the group. If these don't deter other hermit crabs, they may seek them out and try to rip them out of their shell. These animals are also masters of reusing shells. When a new shell turns up, they form a line with the largest crab at the front and the smallest crabs near the back. If the largest hermit crab wants to change its shell, then the next smallest crab will take the old shell starting a hand-me-down line, and they'll change their shells for different reasons.

(13:46): Sometimes they'll choose a new shell because they get sick of their old one or they outgrow it, but their shells can also become degraded or broken from attacks by predators or worn down by the elements. And remember that in order to grow, hermit crabs have to molt their old exoskeleton off to form a new one. The new skeleton grows under the old one and splits it open, allowing for the exoskeleton to fall off on its own. The new skeleton starts off soft and takes some time before it's able to harden. Some hermit crabs will also eat their exoskeletons because they can carry some nutrients to help them grow while their exoskeleton is hardening. Hermit crabs can dig a hole in the sand so they have protection. Molting takes anywhere between 45 and 120 days and newly molted hermit crabs have a blue color to communicate amongst themselves.

(14:40): Hermit crabs make a noise by ululation is basically making noise By rubbing two body parts together, it's believed that they rub their legs together or knock their legs against the inside of their shell. To make this sound, it sounds like a cross between a frog's croak and the chirping noise Crickets make. They can also make this sound to ward off predators and if they're stressed out, not only are hermit crabs, lovable animals, they're also crucial to the ecosystems that they live in. They're an important food source for many animals like fish, sea stars, birds, and crabs. As mentioned earlier, they're also super helpful at cleaning up the environment by scavenging and acting as decomposers. They clean the oceans of dead and decaying organisms, and through their waste, they deposit those nutrients back into the ecosystem for other organisms to take in. This helps to keep a healthy food web.

(15:39): Unfortunately, they're facing a lot of problems caused by humans. One of their greatest dangers right now is pollution in the ocean. Plastic pollution is incredibly harmful to hermit crabs because they often see plastic bottle caps and containers and mistake them for potential shells, and because of this, they'll end up dying. Studies have shown that up to half a million hermit crabs die every year because they're caught in plastic debris. That study was conducted on two southern Pacific islands, so there are bound to be more deaths that were not accounted for elsewhere in the world. After trapped hermit crabs die, they released pheromone signals to other hermit crabs. When they received that signal, they flocked those same bits of plastic detritus leading to a constant cycle of hermit crabs dying, and then luring others to their deaths. Some species of hermit crabs are on the decline and have been placed in the near threatened category.

(16:38): The coconut crab, which is the largest terrestrial art pot in the world, has been placed on the vulnerable list by the I U C N. Their populations in the wild are also declining because people will catch them and sell them as pets. If you're looking to buy a hermit crab, don't support places that catch them in the wild. There are places that will breed them in captivity, and it's a much better option. And while they're nice to have as pets, many people mistreat them without even knowing it. Remember that all hermit crabs have gills and terrestrial hermit crabs need very humid air to live a comfortable life. If their enclosure isn't moist enough for them, they can end up slowly suffocating. And as I mentioned earlier in the episode, they're also very social animals. So if there's only one hermit crab in a tank, it could cause them a lot of stress.

(17:29): So if you get a hermit crab, make sure that you're aware of how to take care of one properly. If you want to help hermit crabs and the ecosystems that they live in, check out the Monterey Bay Aquarium, the Ocean Conservancy and Oceana. Thank you so much for coming on this adventure with me as we explored the world of hermit crabs. You can find the sources that we use for this podcast and links to organizations that we reference at onwildlife.org. You can also email us with any questions at On Wildlife dot podcast@gmail.com, and you can follow us on Instagram at On Wildlife, or on TikTok at wildlife. Don't forget to tune in next Wednesday for another awesome episode, and that's On Wildlife.

Jess Avellino (18:23): You've Been listening to On Wildlife with Alex Re. On Wildlife provides general educational information on various topics as a public service, which should not be construed as professional financial, real estate, tax, or legal advice. These are our personal opinions only. Please refer to our full disclaimer policy on our website for full details.