Hermit crabs make for popular pets, in part because of their small size. But these crustaceans won’t stay tiny forever. As a hermit crab owner, it’s important to understand how large your crab can grow. This will help you provide adequate housing and care as your pet matures.
So exactly how big do hermit crabs get? The size depends on the species, but some can reach surprisingly large proportions. With proper care, certain types of hermit crabs can grow to the size of a softball or even larger. Let’s take a detailed look at hermit crab growth.
Average Sizes of Common Pet Hermit Crab Species
There are over 800 species of hermit crabs in the world. But only a handful are commonly kept as pets. Here are the average sizes of some of the most popular hermit crab pets:
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Purple Pincher (Caribbean) Hermit Crab: These have distinctive purple claws. They average 2-3 inches long as adults but can reach up to 5 inches. Their weight ranges from 100-500 grams.
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Ecuadorian Hermit Crab One of the smallest species, these crabs reach just 0.4-1 inch long and weigh 28-50 grams.
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Strawberry Hermit Crab Named for their reddish color, these crabs average 3-4 inches long and 50+ grams They can reach up to 6 inches long
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Indonesian Hermit Crab: The giants of the hermit crab world, these average 5-6 inches long and weigh around 160 grams. They can grow up to 8 inches long.
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Ruggie (Australian) Hermit Crab: These average 2-2.5 inches long and 60 grams, growing up to 4 inches long.
So while most pet hermit crabs stay relatively small, certain species can get surprisingly big. The Indonesian hermit crab is the largest, regularly exceeding 6 inches long as an adult.
What Impacts Maximum Hermit Crab Growth?
Several factors influence just how large an individual hermit crab will get:
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Species: Some species are genetically predisposed to be larger. Indonesian and Caribbean hermit crabs reach much bigger sizes than Ecuadorian crabs.
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Age: Given enough time, hermit crabs continue growing throughout their lifetimes. The oldest individuals tend to be the largest.
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Molting: To grow, hermit crabs must periodically shed their exoskeletons. Regular, successful molting enables more growth.
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Diet: Proper nutrition provides the fuel and materials for growth. Well-fed hermit crabs can reach larger sizes.
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Habitat Size: Hermit crabs raised in spacious enclosures with room to exercise and forage tend to grow bigger than crabs kept in tiny tanks.
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Origin: Interestingly, wild-caught hermit crabs often grow significantly larger than crabs bred in captivity. Even individuals of the same species reach bigger sizes when collected from the wild.
So with the right genes, age, nutrition, habitat, and origin, some hermit crabs can attain impressive proportions. Next let’s look at exactly how they achieve such growth.
The Hermit Crab Growth Process
Hermit crabs grow by molting, or shedding their exoskeletons. Here is what happens:
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As a hermit crab eats and matures, its body grows too large for its rigid exoskeleton.
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When the exoskeleton becomes restrictive, the hermit crab stops eating and burrows underground.
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Under the sand, the crab forms a new soft exoskeleton under the old one.
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Then the old outer shell splits open and is discarded.
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At this point, the hermit crab is completely vulnerable until its new exoskeleton hardens. This process can take weeks.
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Once the new exoskeleton hardens and the crab digs up to the surface, it will be noticeably larger.
Hermit crabs must repeat this molting process regularly throughout their lives to continue growing. Younger crabs may molt every few weeks, while older crabs molt just a few times a year.
Interestingly, hermit crabs can shrink slightly with a molt too. But overall, successive molts allow them to achieve impressive sizes. Large hermit crabs may be 30+ years old and have molted hundreds of times.
Caring for Growing Hermit Crabs
If you own a hermit crab, it’s essential to accommodate its growing needs. Here are some tips:
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Get a large habitat. Choose an enclosure with lots of floor space and vertical climbing room. Aim for at least 10 gallons per crab.
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Use big shells. Offer a variety of larger shells so your crab can fully withdraw into a properly fitting shell as it grows.
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Provide protein. Incorporate protein sources like shrimp, nuts, and insects into your crab’s diet to fuel growth.
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Maintain proper heat/humidity. Optimal temperature (70-80°F) and humidity (70-80%) supports molting and growth.
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Allow deep substrate. Sand or coconut fiber 6+ inches deep gives burrowing room for molting.
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Limit handling. Resist touching your crab for at least a week before and after molting to avoid disturbing the process.
With the right habitat and care, many pet hermit crabs can achieve their maximum genetic size potential and live long, healthy lives. It’s amazing to watch these small creatures grow into GIANT crabs over decades!
Coenobita clypeatus Land hermit crabs live close to the shoreline and must have access to both land and water. They are popular pets but do not breed in human care. Consequently, the pet trade harvests them from the wild, which is unsustainable.
A hermit crabs front half is covered with a hard exoskeleton, like that of most other crabs. Its long abdomen has a softer exoskeleton, which can adapt to fit into a spiraled snail shell. A hermit crab presses its abdomen, its fourth and fifth pairs of legs, and the appendages at the end of its abdomen (called uropods) against the shells inner wall by contracting its longitudinal muscles.
Its large, left uropod hooks to the center post of the shell. It is used for defense, holding onto tree limbs and balance. The smaller, right claw and the next pair of appendages, which also have claws, are used for collecting and passing food and water to the crabs mouth. Rough surfaces help hold the crab in the shell.
Hermit crabs have reduced gills, and their moist gill chambers have highly vascularized areas for gas exchange. They have stalked eyes with acute vision, and two pairs of antennae. They use the longer pair for feeling and the shorter, feathery pair for smelling and tasting. They also have sensory hairs that are part of the exoskeleton. They use these hairs and their antennae as vibration sensors.
Hermit crabs molt as they grow, shedding their exoskeletons and creating new, larger ones to accommodate their larger bodies. A crab molts by building up enough water pressure in its body to split its old shell. Some crabs leave their shell and bury themselves in sand to molt. Some species store water in their shell before molting and remain in the shell throughout the molt, which may take from 45 to 120 days.
You can tell that a crab is freshly molted when it has a clean, bluish color. A crab may eat its molted shell, possibly for its calcium, vitamins and minerals.
When selecting a new shell, a hermit crab follows a series of steps:
- Explore the shell visually
- Test the shell for movability
- Explore the shells surface texture
- Explore the external shape of the shell
- Test the shells opening (Is it clear? Can the hermit crab get in?)
- Check the internal size to see if it can make a snap withdrawal
- Turn the shell upside down to make sure it can right itself again
Hermit crab species come in a range of sizes, from a fraction of an inch (a few millimeters) to nearly the size of a coconut.
Many different species of land hermit crabs live in tropical areas of the Indo-Pacific region, the western Atlantic and the western Caribbean.
Land hermit crabs live close to the shoreline and must have access to both land and water. They use pools and crevices of sea water to wet their gills and the interiors of their shells, and they reproduce and spend their early stages in water. Other hermit crab species are entirely aquatic.
Hermit crabs are omnivorous scavengers. They eat whatever they find, although not the former occupants of the shells they use.
At the Smithsonians National Zoo, land hermit crabs are fed crab food and assorted fruits and vegetables.
Hermit crabs mate in seawater. Before mating, the male holds the female with one claw, and then taps or strokes her with the other or pulls her back and forth. Both crabs emerge partially from their shells, placing their stomachs together to mate.
After the eggs hatch, the larvae go through several aquatic life stages and molts. When adulthood is reached, the crabs migrate to shore for a terrestrial life.
Hermit crabs are extremely popular pets and are readily available in pet stores, particularly those with nearby access to the ocean. However, the hermit crab pet business is unsustainable. Hermit crabs do not breed in human care; they return to the ocean to breed and live out the first part of their lives. As a result, all hermit crabs purchased through pet shops come from the wild.
Land hermit crabs are also at risk of habitat loss, as the mangroves and coastal areas where they live are taken over and developed by humans.
- Choose your pets wisely, and do your research before bringing an animal home. Exotic animals don’t always make great pets. Many require special care and live for a long time. Tropical reptiles and small mammals are often traded internationally and may be victims of the illegal pet trade. Never release animals that have been kept as pets into the wild.
- Avoid single-use plastics, such as plastic bottles, bags and utensils. Choosing reusable options instead can help reduce plastic pollution.
- Protect local waterways by using fewer pesticides when caring for your garden or lawn. Using fertilizers sparingly, keeping storm drains free of litter and picking up after your pet can also improve watershed health.
- Save water by switching to low-energy appliances, fixing leaks and turning off faucets when they arent in use.
- Hermit crab species come in a range of sizes, from a fraction of an inch to nearly the size of a coconut.
- A crab may eat its molted shell, possibly for its calcium, vitamins and minerals.
- lcLeast Concern
- ntNear Threatened
- vuVulnerable
- enEndangered
- crCritically Endangered
- ewExtinct in the Wild
- exExtinct
- ddData Deficient
- neNot Evaluated
Hermit Crab changing shells
FAQ
How long does it take for a hermit crab to grow full size?
As pets, they do best when kept in groups of two or more. Habitat size: Hermit crabs reach adult size in 2 years under ideal conditions, depending on species; upgrade the habitat size as your hermit crab grows. Provide at least a 10-gallon tank for up to two hermit crabs.
Do hermit crabs like being held?
Hermit crabs generally don’t like being held in the same way a dog or cat might enjoy human interaction. They are more likely to tolerate handling, especially if they have been socialized to it, but they are still prone to stress when removed from their tank.
How big do pet store hermit crabs get?
Hermit Crabs can grow up to 4 inches and do well as pets when a few basic needs are met.
What is the lifespan of a hermit crab?
Hermit crabs can live for a surprisingly long time, with some species in captivity reaching 10-20 years with proper care, and even longer in the wild, potentially exceeding 30 years. Many factors influence their lifespan, including species, diet, and environmental conditions.