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Surface Moulting - A Hermit Crab Emergency

Updated: Aug 19, 2023

Hermit Crab Moulting is a delicate process that should take place entirely beneath the substrate. Unfortunately, this is not always the case and sometimes, your Hermit Crab may surface moult.

This is an instant emergency and could be a matter of life or death if not handled straight away.

Being an Arthropod, Hermit Crabs need to moult in order to grow. You can read all about Hermit Crab moulting in our post here

In the meantime, let's talk about surface moulting.

What does a surface moult mean?

Surface moulting is when a Hermit Crab goes through the process of moulting, above the substrate and out in the open. This is extremely dangerous, if not handled appropriately, it is often a death sentence.

So, why do Hermit Crabs choose to surface moult instead of safely moulting beneath the substrate? There is a large variety of factors that come into play when a surface moult happens. This is not your Hermit Crabs preferred method and is usually a last resort.

Below are some reasons as to why a surface moult may occur.

  • Inadequate Substate Depth - Australian Hermit Crabs need a minimum of 6 inches (15cm) of substrate. This is so they have enough depth to dig down and moult safely without being found and attacked by an intruder. Often a Hermit Crab will use the entire depth and moult at the very bottom of the tank. If you have room to go deeper than 15cm, you should. A tank with very low substrate will not give your crab the space it needs to moult, and more often than not, they will have no other choice but to surface moult.

  • Incorrect Substrate Mixture - Australian crabs require 8 parts play sand to 1 part of damp coir peat to create a stable and moist substrate to safely moult in. The use of plain sand, plain coir peat, reptile bedding, dirt, pebbles or rocks and tanbark are all extremely unsuitable substrates. If these substrates are used in the tank, the crab will have no other option than to surface moult.

  • Stress - When Hermit Crabs are plucked from the wild and sent to pet stores, they are under a huge amount of stress. This is made worse by the fact that most pet store tanks are highly inappropriate. It is common for Hermit Crabs to surface moult while in pet store tanks, sometimes they can still be in quite a stressed state from their time at the pet store and can surface moult soon after you take them home. If you house your Hermit Crabs in a stressful environment (too much handling, no privacy, overcrowding, unsuitable conditions etc.) this can cause enough stress to cause your crab to surface moult.

How can you tell the difference between a surface moult or a dead crab?

It can be very difficult to tell the difference between a dead Hermit Crab and a surface moult, due to the similarities in appearance.

When a crab moults, it appears life-less with minimal movement, and hanging partially out of their shell. When a crab has passed away, they will be dangling out of their shell in a similar way to when they moult, however, they may have a fishy smell to them and will often fall out of their shell when picked up, which is a clear indication of death. If you are still unsure, watch the crab closely for an extended period of time, if you see any slight twitches or jerks, your crab is surface moulting.

Follow the below steps if you find a surface moulting Hermit Crab.

  • Create an isolation tub immediately for the moulting crab, this should include either a small amount of prime water in the bottom or some damp moss or substrate.

  • Gently scoop up the moulting crab with a spoon, being careful not to touch them (dig up the sand underneath them with the spoon as you lift them up) Place them gently into the isolation tub. This tub should not contain anything else.

  • Place the isolation tub back into the main tank and cover with something to keep it dark, your crab needs privacy (a cloth or towel will be fine)

  • If you have found the crab mid-way through their moult and they have released their exoskeleton, do not throw this away! This must be placed into the isolation tub with the moulting crab so that they can consume it. It is very important that they consume their old exoskeleton to help them gain back their strength and receive the necessary calcium to help their new exoskeleton harden.

  • Your surface moulting Hermit Crab should be isolated for the duration of the moulting process. Once they have consumed their exoskeleton, their new exoskeleton has hardened and they are happily moving around and eating/drinking, they can then be re-released into the tank with the rest of the crew.

FAQ on surface moulting -

Why is surface moulting so dangerous? When a Hermit Crab moults, they shed their hard outer exoskeleton, leaving them with a soft and vulnerable exoskeleton. This makes them a very easy target for other Hermit Crabs to consume them.

Should I add food and water to the isolation tub? No, this should only be added after the crab has completed their moult and is up and moving about.

When should I move my crab back into the main tank with the rest of my crabs? Your crab is ready to be moved out of isolation once it has consumed most of its old exoskeleton, the new exoskeleton has hardened, and the crab is up and moving around confidently.

What do I use for an isolation tub?

One of the best things you can use is an actual isolation tub, these are small clear plastic containers with a secure lid and holes for air flow. If you have not pre-purchased one of these, you can use a Tupperware container and prick some holes in it for airflow.

What if I am still not sure if my crab is surface moulting or dead? Many surface moulting crabs have sadly been disposed of by their owners because they assumed them to be dead. If in doubt, treat it as a surface moult. You will know in due time if the moult is not progressing, and the crab begins to smell.

*A Hermit Crab surface moulting in an isolation tub.

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