Hermit crabs, with their distinctive habit of occupying discarded shells, are fascinating and unique creatures, and these invertebrates are a vital part of the ocean’s ecosystem. Despite their name, hermit crabs are not true crabs, and their behaviour, biology, and habitats demonstrate just how diverse marine life is.
What is a hermit crab?
Hermit crabs (Paguroidea), are classified as invertebrates, meaning they lack a backbone. Like true crabs, hermit crabs have an exoskeleton that protects them instead of a backbone. However, one of the major differences between these two types of crab is that hermit crabs have evolved to use discarded snail shells for additional protection. Interestingly, they are more closely related to lobsters than crabs.
How many species of hermit crabs are there?
There are over 800 known species of hermit crabs, divided broadly into land and aquatic categories. Land hermit crabs live predominantly on land but must return to the sea to breed. Aquatic hermit crabs, such as those in the genus Pagurus, spend their lives underwater. Both subsets of hermit crabs have slightly different variations to allow them to adapt to their environments.
One particularly notable species is St Piran’s hermit crab (Clibanarius erythropus), which has recently been observed returning to UK waters after a long absence. This rare find highlights the ever-changing nature of marine environments.
What do hermit crabs look like?
Hermit crabs vary significantly in size, shape, and colour depending on their species. Generally, they possess a hard exoskeleton on the front part of their bodies, while their abdomens remain soft and vulnerable. For this reason, they seek out shells to protect themselves. These shells, borrowed from other molluscs, can vary widely in appearance and size, reflecting the diversity of environments that hermit crabs inhabit.
Why do hermit crabs change shells?
Hermit crabs change shells as they grow. As a hermit crab matures, it outgrows its current shell and must find a larger one to accommodate its increased size. This process is vital for survival, offering both protection from predators and a safeguard against environmental factors. Hermit crabs are known to engage in ‘shell fights’, where they compete for better-fitting shells.
Once a hermit crab has abandoned its chosen shell, another crab will usually make use of it, creating an aquatic recycling scheme.
What do hermit crabs eat?
Hermit crabs are omnivores, meaning their diet includes both plant and animal matter. They typically scavenge for food, eating algae, decaying wood, leaf litter, and dead fish. This scavenging behaviour helps keep their ecosystem clean, as they recycle nutrients back into the environment.
Where do hermit crabs live?
Hermit crabs can be found in a variety of habitats, from tropical coral reefs to temperate coastlines. They often inhabit rock pools, sandy beaches, and seagrass beds. When rockpooling, it’s important to be respectful of their habitats. Disturbing these environments can harm the delicate balance that hermit crabs and other creatures rely on. Always observe and enjoy marine life without taking anything from these natural settings.
How long do hermit crabs live?
The lifespan of hermit crabs varies widely among species. In the wild, some hermit crabs can live for an average of 5 years, although some pets can live longer. In captivity, with proper care, land hermit crabs often live for 10-20 years. Their longevity depends on a range of factors, including diet, environment, and the availability of suitable shells. If a hermit crab cannot find an appropriate shell, it can be left extremely vulnerable to predators.
Do hermit crabs have relationships with other creatures?
Hermit crabs have symbiotic relationships with several other marine organisms. One well-known example is their association with parasitic sea anemones. These anemones attach to the shell of a hermit crab, benefiting from increased mobility and access to food scraps.
In return, the parasitic anemones provide protection with their stinging tentacles, deterring potential predators from attacking the hermit crab.
Hermit crabs are captivating creatures that play a vital role in their ecosystems. Their unique behaviours and relationships with other marine life highlight the complexity and interconnectedness of ocean habitats.
If you’re interested in seeing hermit crabs up close, visit our Warm Seas exhibit, where you can learn more about these intriguing invertebrates and their tropical homes.
Book your tickets now to see these nomadic sea creatures up close!