The Ultimate Guide to Hermit Crabs: How Big Can They Really Get?

Hermit crabs are fascinating creatures that are often kept as pets. They are unique in that they have a soft, spiraled abdomen which they protect by occupying the shells of other sea creatures. This makes them incredibly adaptable to different environments, as they can switch shells as needed to fit their changing needs.

One aspect of hermit crabs that many people find intriguing is their size. While some species can be quite small and delicate-looking, others can grow to surprising proportions.

As a result, it’s not uncommon for people to wonder just how big a hermit crab can get. In this article, we’ll explore the topic of hermit crab size in detail.

We’ll discuss the different species of hermit crabs and their varying sizes, examine the factors that influence how large they can grow, and highlight some examples of particularly large hermit crabs found in nature. So if you’re curious about these fascinating creatures and want to learn more about just how big they can get, read on!

What is a Hermit Crab?

Hermit crabs are unique creatures that belong to the crustacean family. Unlike other types of crabs, they don’t have a hard shell covering their whole body.

Instead, they have a soft abdomen that remains unprotected and vulnerable to predators. To stay safe, hermit crabs use empty snail shells as homes, which they can carry around on their backs.

Hermit crabs are found in various parts of the world and live in both saltwater and freshwater habitats. They’re known for their distinctive appearance and behavior, making them popular pets for many people.

How do Hermit Crabs Differ from Other Types of Crabs?

Hermit crabs differ from other types of crabs in several ways. Firstly, their soft abdomen is not protected by a hard shell like many other crustaceans.

Instead, they use snail shells or other objects to protect themselves from predators and environmental factors. Secondly, hermit crabs have two pairs of antennae that are used for sensing their surroundings and finding food.

They also have ten legs; two relatively large claws used for defense or obtaining food, two small walking legs at the front end of their body called chelipeds which help them hold onto things like food while eating or climbing over rocks; four walking legs with sharp ends called dactyls used for moving around; and two back legs which work like paddles when swimming underwater. Hermit crabs don’t have teeth like most creatures but instead, have a specialized organ called the gastric mill located inside the stomach that grinds up food particles before digestion.

The Basic Anatomy of a Hermit Crab

Hermit crab anatomy is fascinating because it’s so different from other types of crabs. Their body has three distinct parts: the head (cephalon), thorax, and abdomen.

The head is the smallest part of their body and consists of two pairs of antennae, a pair of eyes, and a mouth. The thorax is the largest part of their body and contains four pairs of walking legs, two claws or chelipeds for defense or grabbing food, and a pair of small organs called maxillipeds that help them process food.

The abdomen is the softest part of their body and contains their reproductive organs and digestive system. One unique feature of hermit crabs is their ability to molt or shed their exoskeleton as they grow.

During this process, they become softer than normal until they can form a new shell. Molting can take anywhere from several hours to several days to complete depending on the size of the crab.

The Size of Hermit Crabs

Hermit crabs are fascinating creatures that come in a variety of shapes and sizes. While some species are relatively small, others can grow to be quite large.

The maximum size that a hermit crab can reach depends on several factors, including genetics, environmental conditions, and food availability. One of the smallest species of hermit crab is the Caribbean hermit crab.

These tiny crabs only grow to be about 1 inch in length and are commonly kept as pets. They have bright red or orange bodies with white spots and black eyes.

Despite their small size, Caribbean hermit crabs are very active and can often be seen scurrying around their tanks. On the other end of the spectrum are the coconut crabs, which are some of the largest hermit crabs in the world.

These massive crustaceans can grow up to 3 feet in length from leg tip to leg tip and weigh up to 9 pounds! Coconut crabs live primarily on land rather than in water like most other crustaceans, and they have adapted well to this lifestyle by developing thicker shells and stronger legs for climbing.

Another large species of hermit crab is the red-legged hermit crab, which grows up to about 2 inches long. These crabs are found throughout the Caribbean Sea and have bright red legs that contrast with their greenish-brown bodies.

Red-legged hermit crabs often inhabit areas with lots of rocks or coral where they can scavenge for food. The strawberry land crab is another impressive species of hermit crab that can grow quite large.

Found primarily in South America, these land-dwelling crustaceans have bright red shells with white spots and black-tipped claws. Strawberry land crabs can grow up to 6 inches long from head to tail, making them one of the largest terrestrial arthropods around.

Hermit crabs come in all shapes and sizes. While some species are very small, others can grow to be quite large.

The maximum size that a hermit crab can reach depends on several factors, including genetics and environmental conditions. Whether you’re interested in keeping these fascinating creatures as pets or you simply enjoy learning about different types of marine life, there’s no denying that hermit crabs are truly amazing animals.

Factors that Affect the Size of a Hermit Crab

Environmental Factors

The size of a hermit crab is not solely determined by genetics. Environmental factors also play a significant role in determining how big a hermit crab can get. One important factor is food availability.

A hermit crab that has access to an abundance of food will grow faster and larger than one that struggles to find enough food. Habitat size is another environmental factor that can impact the size of a hermit crab.

Crabs that are housed in small habitats may not have enough space to move around and grow properly. On the other hand, crabs in larger habitats tend to be healthier and grow bigger due to increased access to resources and exercise opportunities.

Water quality is also an important environmental factor affecting the growth rate and overall health of a hermit crab. Poor water quality can lead to health problems, which can ultimately limit growth potential.


While environmental factors have an impact on the size of a hermit crab, genetics also play an important role. Different species of hermit crabs have different maximum sizes they can reach due to their genetics. For example, some species naturally grow larger than others because they evolved in environments with different selective pressures or because they inherited genes from their parents for large size.

Within each species, there may also be variation in maximum size based on individual genetic variability. It’s worth noting that genetic mutations or abnormalities may lead some individuals within a given species to exceed typical maximum sizes as well as slow-growing ones failing ever reach normal sizes for their age or even developing deformities.

The Role Environment and Genes Play

Environmental factors such as food availability, habitat size, and water quality; as well as genetic factors like natural variability among individuals or between species affect how big a hermit crab can get. The right environmental conditions, combined with favorable genetics, can lead to larger and healthier hermit crabs. Therefore, it’s important for hermit crab owners to provide the best possible habitat for their pets to ensure optimal growth and health.

Examples of Large Hermit Crabs

Hermit crabs come in a variety of shapes, sizes, and colors. While most species are relatively small, there are a few that stand out for their impressive size. Two of the largest known species of hermit crabs are the coconut crab and the Japanese spider crab.

The Coconut Crab

The coconut crab (Birgus latro) is the largest land-living arthropod in the world. These crabs can grow up to 3 feet in length from leg tip to leg tip and can weigh as much as 9 pounds.

Found on islands throughout the Indian Ocean and parts of the Pacific Ocean, coconut crabs are named for their ability to climb palm trees and crack open coconuts with their powerful pincers. One unique feature of the coconut crab is its ability to breathe both on land and underwater.

While most hermit crabs rely on a moist environment to breathe through their gills, the coconut crab has evolved modified gills that allow it to extract oxygen from air instead. Another fascinating adaptation of the coconut crab is its highly sensitive sense of smell.

The crab’s antennae contain thousands of tiny receptors that help it detect food from great distances. This is especially important since they need a lot of food to sustain their large size.

The Japanese Spider Crab

The Japanese spider crab (Macrocheira kaempferi) is another giant among hermit crabs – it has been known to reach lengths up to 12 feet across including its legs! Found along the coastlines around Japan, these crabs can weigh up to 40 pounds. One unique physical characteristic of this species is its long, spindly legs which allow it to move quickly across sandy or rocky ocean floors.

Despite their impressive size and strength, Japanese spider crabs are relatively docile and prefer to scavenge for food instead of actively hunting. Another interesting fact about the Japanese spider crab is their lifespan.

These crabs can live up to 100 years in the wild, making them one of the longest-living arthropods in the world. They also have some unique adaptations to help them survive for such a long time, including a specialized immune system and regenerative abilities.


Hermit crabs are fascinating creatures that have captured the hearts of many. Their unique appearance and behaviors make them a popular pet choice for animal enthusiasts around the world. While many people may wonder how big these little crustaceans can get, the truth is that it varies greatly depending on the species and individual crab.

As we’ve discussed, environmental factors play a significant role in determining the size of a hermit crab. Factors such as food availability, habitat size, and water quality can all impact the growth rate and ultimate size of a crab.

Genetics also play a role in determining the maximum size that a particular species or individual can reach. Despite the variability in size, there are some impressively large hermit crabs out there!

The coconut crab, for example, is one of the largest arthropods in existence with some individuals reaching sizes of up to three feet long! The Japanese spider crab is another impressive species known for its massive leg span that can reach up to 12 feet wide!

While there is no definitive answer to how big a hermit crab can get, one thing is certain: these little creatures are truly amazing! Whether you’re an animal enthusiast looking to keep one as a pet or simply someone who appreciates nature’s wonders from afar, hopefully this article has given you some insight into just how incredible these tiny crustaceans really are.


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