How Big Can Hermit Crabs Get

 How Big Can Hermit Crabs Get


How Big Can Hermit Crabs Get: Hermit crabs are a captivating and diverse group of crustaceans known for their unique lifestyle. They are remarkable for their habit of occupying discarded shells of other marine creatures, which they use as protective shelters. Yet, what often piques curiosity is the question of just how large these hermit crabs grow.

As the size of a hermit crab depends on various factors, including its species, environment, and available resources. Hermit crab species range in size from minuscule specimens that measure mere millimetres to colossal giants that can span several inches in length. 

One of the most impressive species in terms of size is the coconut crab, often considered the largest terrestrial arthropod. It is not uncommon for these crabs to reach sizes of up to three feet in leg span and weigh several pounds. However, when we think of hermit crabs, we often envision the more commonly encountered marine hermit crabs, which come in a wide range of sizes and exhibit fascinating behaviors in response to their ever-growing need for larger shells.

We will delve into the world of hermit crabs to understand the factors that influence their size, the strategies they employ to find suitable shells, and the incredible adaptations that allow them to thrive in various habitats. Whether you’re a marine enthusiast or simply curious about the wonders of the natural world, this journey into the realm of hermit crabs will reveal the astonishing diversity in their sizes and lifestyles.

How Big Can Hermit Crabs Get

How big is the biggest hermit crab?

Diogenes (commonly referred to as the giant hermit crab) happens to be the largest of the hermit crabs discovered (Wood and Wood, 2000), with a body up to 30 cm long. According to the Smithsonian Marine Station at Fort Pierce (2010), this species has blue or greenish eyes with red and white-banded antennae (Fig. 1).

The title of the largest hermit crab is often bestowed upon the remarkable coconut crab (Birgus latro), a true giant of the crustacean world. These remarkable creatures, native to islands in the Indian and Pacific Oceans, can reach astonishing sizes, with leg spans of up to three feet and weights exceeding several pounds. Their colossal size is matched only by their incredible strength, allowing them to crack open coconuts with their powerful pincers.

The coconut crab’s enormous proportions are a testament to the adaptability of hermit crabs. Unlike their marine cousins, coconut crabs are primarily terrestrial, inhabiting the tropical forests of their native islands. Their size is a result of evolution’s response to the need for protection on land, where larger shells and more substantial bodies offer better defense against predators.

Observing the coconut crab’s sheer size and strength, one cannot help but marvel at the diversity and ingenuity of nature’s creations. These extraordinary hermit crabs serve as a testament to the remarkable evolutionary paths that different species can take, demonstrating how size can be a key factor in their survival and adaptation to their specific environments.

How big is a 10 year old hermit crab?

Hermit Crabs under a golf ball size would most probably be under ten (10) years of age, and medium size (mandarin size) at least in their twenties (20+). The photo to the left shows the change in size over 25+ years of growth in captivity.

The size of a 10-year-old hermit crab can vary significantly depending on its species, environmental conditions, and access to resources. Hermit crabs, like many creatures, grow at different rates, and their final size is influenced by various factors.

In general, a 10-year-old hermit crab is likely to be larger than a juvenile or newly hatched crab. By this age, it may have gone through several molting cycles, during which it sheds its exoskeleton to accommodate its growing body. The frequency and success of molting can impact a hermit crab’s size. If it has experienced favorable conditions with an abundance of food and appropriate-sized shells for shelter, it may have grown larger than individuals facing less favorable circumstances.

The size of a 10-year-old hermit crab can range from a few centimeters in smaller species to several inches in larger species. Some hermit crabs reach their maximum size relatively quickly, while others continue to grow throughout their lives, albeit at a slower pace.

Ultimately, the specific size of a 10-year-old hermit crab is a product of its unique life history and experiences, making each individual a testament to the complexity and adaptability of these fascinating crustaceans.

How big do normal hermit crabs get?

Hermit Crabs can grow up to 4 inches and do well as pets when a few basic needs are met. A 10 gallon terrarium is sufficient for up to 6 small (<2″) Hermit Crabs, while larger crabs (3 ½”+) will need a 20 gallon terrarium and can be housed with 3 or 4 crabs.

Normal hermit crabs, often found in marine environments, come in a variety of species, each with its own typical size range. While there is no one-size-fits-all answer to how big “normal” hermit crabs get, we can discuss a general size range for these common crustaceans.

On the smaller end of the spectrum, some hermit crab species, such as the tiny “pygmy” hermit crabs, may measure just a few millimeters in length. These diminutive hermit crabs inhabit the discarded shells of small gastropods.

In contrast, larger marine hermit crab species can reach sizes of several inches, with some growing up to around 6 inches (15 centimeters) in length, including their shell. These larger hermit crabs are often encountered in intertidal zones and deeper ocean waters, and they inhabit a variety of shell types, including those of snails and mollusks.

It’s important to note that the size of a hermit crab can also change as it grows and molts. During molting, hermit crabs shed their exoskeletons and then select a larger shell to accommodate their growing bodies.

The size of “normal” hermit crabs varies depending on their species, with some being quite small and others reaching several inches in length. Their size can also change as they go through molting cycles and find new shells to inhabit.

Do hermit crabs bite?

Hermits are not aggressive and they do not bite, but they will reach out and try and hold on with their pincher claw. They usually are passive, if they are held incorrectly they will grab your skin to hold on. You can actually release a hermit claw by running it under warm water to opening his pinchers with a tweezers.

Hermit crabs are capable of biting, but it’s important to clarify that their bites are typically not harmful to humans. Hermit crabs have small pincers or claws that they use for various purposes, including feeding, grooming, and defense. When they feel threatened or are handled roughly, they may use their pincers to pinch in self-defense.

These pinches are usually more startling than painful to humans, as hermit crabs are not equipped with powerful jaws or venomous bites. The level of discomfort experienced during a hermit crab bite can vary depending on the size of the crab and the sensitivity of the person being bitten. In most cases, the pinch feels like a brief, sharp nip.

It’s essential to handle hermit crabs gently and with care to avoid causing them stress or prompting them to use their pincers defensively. If you’re concerned about being bitten, it’s advisable to avoid handling them excessively or unnecessarily.

In their natural habitat, hermit crabs are not aggressive toward humans and primarily use their pincers for interactions with other crabs or for finding and handling food. So while hermit crabs can bite, it’s generally not a cause for major concern for those who handle them responsibly and with respect for these intriguing creatures.

Do hermit crabs lay eggs?

Depending on the size of the female crab, thousands of eggs are laid and deposited with the aid of the gill grooming appendages on her pleopods along the left side of her abdomen.

This may come as a surprise to many, as these fascinating creatures are often associated with their unique habit of occupying abandoned shells rather than their reproductive behaviors. When it comes to reproduction, female hermit crabs typically carry a clutch of fertilized eggs in a special brood pouch located near their tails. The male transfers sperm to the female during a ritualized courtship, allowing her to fertilize her eggs as she carries them.

Once the eggs are fertilized, the female carries them for several weeks, providing protection and a suitable environment for development. It’s important to note that the process of reproduction can be quite vulnerable for hermit crabs. Predators often target females carrying eggs, making it a critical phase of their life cycle.

After a period of incubation, the female will eventually release the tiny, fully-formed hermit crab larvae into the ocean. These juveniles are equipped with specialized adaptations that allow them to survive and grow, eventually finding their own shells to inhabit as they mature. This unique life cycle showcases the remarkable adaptability and resilience of these intriguing creatures in the intricate web of marine life.

Can I influence the size of my hermit crab?

While you can’t directly control the size of a hermit crab, you can certainly influence its overall health and well-being, which in turn can affect its growth. Providing the right environment and care is essential for a hermit crab’s development.

Offering a spacious and stimulating enclosure with a variety of shells for them to choose from is crucial. The availability of appropriately-sized shells allows a hermit crab to find a comfortable fit and encourages healthy growth. A stressed or cramped crab may struggle to molt properly, which can lead to growth issues.

Diet plays a significant role as well. Offering a balanced and nutritious diet, including a variety of foods like fresh fruits, vegetables, and high-quality commercial crab food, can support their growth and overall health. Calcium-rich foods, such as crushed eggshells or specialized supplements, are especially important for proper shell development.

Maintaining a stable and appropriate temperature and humidity level within their habitat is also crucial. Hermit crabs are ectothermic, meaning they rely on their environment to regulate their body temperature. A stable and suitable environment encourages healthy metabolic processes, which contributes to proper growth.

While you can’t directly control the size of your hermit crab, providing a well-maintained, spacious habitat with a diverse diet and proper environmental conditions will create the best conditions for it to thrive and grow to its full potential.

What should I do if my hermit crab outgrows its shell?

If your hermit crab outgrows its shell, it’s crucial to take prompt action to ensure its well-being. When a hermit crab feels cramped in its current shell, it will actively seek out a larger one to accommodate its growing body. Here’s what you can do:

  • Provide a Variety of Shell Options: Offer a selection of shells with different shapes and sizes in your crab’s enclosure. This gives it the opportunity to choose a new home that fits comfortably.
  • Observe and Wait: Keep a close eye on your hermit crab. They are most vulnerable during the molting process, and this is when they’ll be actively searching for a new shell. Be patient and allow them the time and space they need.
  • Ensure Proper Humidity and Temperature: Maintain the appropriate environmental conditions, as a stable and comfortable habitat is crucial for a healthy molt and shell change.
  • Gently Encourage Exploration: You can gently nudge the shells or place them near your crab to entice them to investigate. Be careful not to startle or stress the crab during this process.
  • Avoid Handling: While your crab is in the process of changing shells, it’s best to minimize handling to reduce stress. Let it do its own exploring and settling.
  • Monitor for Signs of Distress: Watch for any signs of stress or illness, such as lethargy, loss of appetite, or unusual behavior. If you notice anything concerning, consult a veterinarian experienced with hermit crabs.

Remember, providing a variety of shells and a comfortable environment is crucial for the well-being of your hermit crab. With patience and the right conditions, your crab will find a new shell that fits, ensuring its continued health and happiness.

Do hermit crabs continue to grow throughout their lives?

Hermit crabs do indeed continue to grow throughout their lives, a phenomenon known as indeterminate growth. Unlike some other creatures, such as insects or reptiles, hermit crabs don’t undergo a final, fixed size. Instead, their growth is ongoing, directly tied to the process of molting.

During molting, a hermit crab sheds its exoskeleton to accommodate its increasing size. This vulnerable period is a critical juncture in their life cycle. Following a successful molt, the hermit crab will seek out a new, larger shell to inhabit, providing ample room for its growing body.

The frequency of molting varies depending on factors like age, environment, and diet. Younger hermit crabs tend to molt more frequently as they experience rapid growth, while older individuals molt less often.

To support this natural process, providing a suitable habitat with a variety of shell options and maintaining proper environmental conditions is essential. A balanced diet rich in calcium also aids in the formation of a sturdy exoskeleton, facilitating successful molts.

The indeterminate growth of hermit crabs is a fascinating aspect of their biology, emphasizing the dynamic nature of these unique creatures as they continuously adapt and evolve throughout their lives.

How Big Can Hermit Crabs Get


The world of hermit crabs is a captivating and diverse one, where size truly matters. From the minuscule to the colossal, these crustaceans display an astonishing range in size, with some, like the coconut crab, reaching remarkable proportions.

Our journey has revealed that a hermit crab’s size is influenced by a complex interplay of factors, including its species, environment, and available resources. The quest for suitable shells, driven by their need for protection and growth, leads these creatures to display remarkable behaviors and adaptations.

Whether it’s the tiny marine hermit crabs that diligently search for their next home or the enormous coconut crabs that inhabit the terrestrial realm, hermit crabs continue to intrigue scientists and marine enthusiasts alike. Their ability to adapt and thrive in various environments showcases the resilience of nature’s creations.

Exploring the question of hermit crab size reminds us of the vast diversity of life on Earth and the importance of preserving ecosystems to ensure the survival of these remarkable creatures. As we continue to study and appreciate these incredible crustaceans, we gain deeper insights into the mysteries of the natural world and the wonders it holds for those who seek to understand it.

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