How Can You Tell How Old a Hermit Crab Is?

Determining the age of a hermit crab can be tricky. Unlike some other pets, you can’t just look up how long their species usually lives and make an estimate that way. Hermit crabs don’t have a set lifespan – their age depends on a variety of environmental and genetic factors. However, there are a few techniques you can use to make an educated guess about your crab’s age.

Look at Their Size

In general larger crabs tend to be older than smaller crabs. Hermit crabs grow by molting – shedding their exoskeleton and growing a larger one. Crabs that are able to molt frequently and have access to larger shells as they grow can reach a very large size. Jumbo crabs (over golf ball sized) are estimated to be at least 10-20 years old. Medium sized crabs (mandarin orange sized) are likely at least in their 20s.

However size isn’t a perfect indicator of age. Some species like the Ecuadorian crab, max out at a smaller size than others, like the Purple Pincher. And a crab that has lost a claw won’t regain its full size until after several molts, making their claw size unreliable for estimating age. Still, all else being equal, a big crab is an old crab.

Examine Their Exoskeleton

As hermit crabs age, their exoskeleton changes texture and develops distinguishing features:

• Older crabs develop more distinct bumps or “nodules” on their claws. These bumps look like teeth lining the inside of the claw.

• Their antennae become thicker and sturdier looking compared to the wispy antennae of younger crabs

• Parts of the exoskeleton develop a rough, almost lobster-like texture instead of the supple softness of younger crabs’ shells.

So if your crab has bumpy claws, chunky antennae, and a shell that’s hardened in spots, it’s likely a more mature crab.

Consider Their History

If you’ve had your crab since it was young, you have the advantage of knowing exactly how long you’ve cared for it. But even if your crab is adopted, you may be able to get clues about its age from its previous home. Was it living with other juvenile crabs, suggesting it might be younger? Or did it come from an owner who had kept crabs for many years, implying a potentially older crab? Every little bit of history helps build a picture.

Learn Their Species

While you can’t judge age by size alone, size plus species can give you more context. For example, a baseball sized Purple Pincher is undoubtedly older than a baseball sized Ecuadorian, since Ecuadorians max out at a smaller size. Learn what’s typical for your crab’s species to better understand what their size suggests about their age.

Check Their Energy Level

Like humans, hermit crabs tend to slow down as they enter their senior years. While this isn’t a perfect measure, a very active, social crab is more likely to be on the younger side compared to a crab that sits still most of the time. Older crabs may still move around and behave normally, just with a little less vigor than they had in their youth.

Consider How Long They’ve Molted For You

Molting offers helpful clues into a crab’s age, since they stop molting once they reach full maturity. If your crab has already molted three times in your care, it’s likely still at least a juvenile with plenty of growing left to do. If it’s gone years without molting, it may be nearing the end of its molting life cycle, suggesting an older crab.

Get Their Otoliths Examined

The only way to know a hermit crab’s age for certain is to have its otoliths examined after it passes away. Otoliths are mineral deposits in the crab’s brain that accumulate annual growth rings, much like a tree. If you truly want an exact age for your crab, this is the definitive (though sad) way to find out.

While we don’t have an easy formula to pinpoint a hermit crab’s age, paying attention to their size, appearance, history, species, activity level, and molting patterns can provide helpful clues. With some sleuthing, you can make an informed estimate to satisfy your curiosity about how old your crab may be. The most important thing, though, is to provide them with the proper care and habitat they need to live a long, healthy life with you, regardless of their age.