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Help! My Hermit Crab Is Foaming!

Most types of crabs can produce bubbles when they are on land. Many land crabs foam at the mouth when they are scuttling about on the beach. Don’t worry about them, they aren’t going to go “mad” and chase you across the beach because of rabies (only mammals can contract that virus). 

The reason most of these wild crabs have bubbles or foam around their mouths is that they are keeping their gills damp. All species of crabs have gills, but some also have small lungs they use when on land. Crabs, including hermit crabs, need to keep their gills damp in order to breathe.

When the air around them is too dry, crabs will bubble, or create a foam around their gills to keep them damp and able to carry out proper respiration. Hermit crabs can do the same, and usually, bubbles aren’t a cause for alarm, but there are some bubbles that require immediate action. 

Here we will go over all the reasons your happy hermit may be foaming when you should worry, and when you don’t have to be alarmed. We’ll also cover what you can do to treat and prevent hermit crab foaming. 

Why Does A Hermit Crab Foam?

Crab on yellow rockweed blowing bubbles or foaming
Regular crab on yellow rockweed blowing bubbles or foaming. This will appear similar on a hermit crab though on a smaller scale.

A hermit crab can start creating foam for a number of reasons. None of them are very good, and some can actually be fatal. So if you see any kind of foam, you should do an inspection to see what is causing the foam. First, though we need to know about the different types of foam and bubbles. 

Clear Foam Or Bubbles Means Their Gills Are Dry

Clear bubbles on your hermit crab are usually from discomfort or low humidity. These things can be fixed easily, but they still need to be addressed quickly. 

The first reason hermit crabs will create clear foam or bubbles is because they are dehydrated and need some moisture on their gills. They are having a hard time breathing, so you should check the enclosure’s humidity levels.

To properly breathe, a hermit crab requires humidity levels of around 70 to 80%. If you see the levels are much lower than this, add some moisture quickly. You can mist your hermit crab with distilled water—never use tap water as the chlorine and other chemicals can be fatal. 

You should also check on their water levels and refill them as necessary. Hermit crabs will bathe in freshwater and saltwater to help keep their gills damp. Make sure they have enough, clean water and there are no obstructions keeping them from doing so. 

Your Hermit Crab Could Be Irritated

Another reason for clear or white bubbling is irritation in the shell. Their abdomen is almost always protected in their shell. Sometimes sand, dirt, or other irritants can get inside and become uncomfortable. 

Typically they will correct this irritation by bathing in the water. They may even crawl out of the shell to remove any caught dirt or sand. But if they are unable to fully submerge or have no access to water they could be foaming to get rid of the irritation.

If your humidity is in the correct range and your hermit crabs are showing signs of clear bubbles, check the bowls of water. You can even pick them up and set them carefully in the water to help relieve the situation.

Stress Or Severe Illness May Produce Brown Bubbles

If you see brown bubbles on your hermit crab, or you notice a fishy, foul smell, unfortunately, your hermit crab may be nearing death. Brown bubbles signify a severe injury, illness, or extreme stress. 

Can Brown Foam On A Hermit Crab Be Treated?

Brown foam on a hermit crab requires immediate action. Be warned though, even with the proper treatment, the hermit crab may not survive. 

What Are The Causes Of Brown Bubbles On A Hermit Crab?

There are several reasons your hermit crab could be spewing brown foam. It could be overheating, suffering from a severe injury, there could be a major stressor in the tank, or it could be post-purchase syndrome.

Let’s dig a little deeper into all of these reasons, and what you can do to help the hermit crab.


Hermit crabs like a warm, humid environment, but there are times it can get too hot, and become very dangerous, especially if the tank is dry. An overheating hermit crab could be foaming up to keep its gills wet so it can breathe, or it may start digging into the substrate. 

Hermit crabs will dig to escape excessive heat because the soil is usually cooler farther down. If you notice combined bubbling and digging, you should check the temp of the tank. 

An ideal air temperature for a happy, healthy, hermit crab is between 72 and 80 degrees Fahrenheit. Check your crabitat temp to make sure it’s somewhere in this range. 

Be sure you don’t have your tank sitting directly in the sun or near a window. The sun coming through the window, then filtering through the tank glass can quickly become overheated and raise the temps significantly. Think of a closed window car in the middle of summer. 

Another thing to check is the tank heater. If you’re using an under the tank heater (UTH), for hermit crabs, this heater should be placed on the side of the enclosure, not the bottom. It can heat up the substrate too high and harm your hermit crabs. 

When they go to molt, or if they try to escape the heat by digging, they will only get hotter and possibly expire.

If you suspect your hermit crab is overheating, take steps to cool the tank to the proper temperature. 


When a hermit crab is injured it could create a foam because it’s breathing harder. Just like we sometimes hyperventilate when we are in pain, a hermit crab can do the same. Except when crabs breathe very quickly, they can create foam on their gills.

Hermit crab injuries are often attributed to fights between crabs. It may be difficult to tell if your hermit crab is hurt, but if you suspect it’s in pain, don’t move it. 

You should separate it from others if it’s not alone so it may be able to heal. Do this by placing a barrier between the injured crab and the others, or moving them into a temporary enclosure. 

If you notice brown bubbles and smell something bad, it usually means the hermit crab is passing away. It may end up getting better, but most times they don’t recover from this type of injury. Just keep it as comfortable as possible during this time. 


Has something changed in the tank? Are there suddenly very loud noises? Is your hermit crab alone? These all could be reasons for stress. 

Try to locate what may be causing the stress to your hermit crab and remove it, or stop what could be causing it to get overly stressed. 

Although they are named “hermit” crabs, they actually thrive with other crabs. In the wild, hermit crabs frequently live in very large colonies. If your little hermit is alone and foaming, it may be a sign of loneliness.

Post-Purchase Syndrome

A newly purchased hermit crab may start bubbling because it is experiencing post-purchase syndrome or PPS for short. Hermit crabs that are bought from beachside tourist shops can especially experience PPS.

They are stored in torture chambers with metal cages (fatal to hermit crabs) with no substrate, dry commercial food (most don’t like to eat this and some can be harmful to their health), and painted shells which are also hazardous to their health.

Anyone would be stressed in that type of environment. If you recently purchased your hermit crab and it’s foaming, most likely this is because of PPS. Make sure you have the correct conditions in your habitat to keep them healthy, and the foaming should stop soon. 

Hermit crabs you get from pet stores or online can also experience PPS. They get shipped, often hundreds, or thousands of miles away. They get stuck in a small box, and travel over land, sea, and air to get to a foreign environment, so be patient when you first get your new pet. 

Other symptoms of the post-purchase syndrome can include lethargy, weakness, loss of appetite, loss of limbs, and even sudden death. When you first get your new hermit crab, try not to handle it or bother it much until it gets used to the new environment. 

You’ll know for sure your hermit crab is feeling better when it starts the molting process. While you probably won’t have to wait for it to start molting to know it’s no longer stressed, this is a sure indicator that it is no longer stressing out. 

Even though it may be detrimental or harmful to its health, hermit crabs will hold off on molting until they are comfortable, and feel safe.

What Is That Single Bubble Attached To Its Abdomen?

Clear, white, or brown bubbles may appear as tiny, foamy, soapy looking suds on the hermit crab or the shell, but sometimes you may notice a black, brown, or grey bubble stuck to the abdomen. 

It will most likely look like it’s growing underneath the shell and could look like a tumor, blood blister, or some other sinister growth. Don’t worry about it though because it’s just an indicator that your hermit crab is about to start molting. 

Molting is a time consuming, often difficult process that can take weeks or even months. During this time they don’t eat, don’t drink, and don’t leave the safety of their burrow. In preparation for this extended “vacation” hermit crabs will often save food. 

That dark bubble on the abdomen is just a food or water pouch. It will disappear after they emerge from their hole and have molted. 

If you haven’t experienced a hermit crab molting process yet, here are a few other signs it’s getting ready:

  • Digging
  • Excessive eating and drinking
  • Lethargy
  • Restlessness
  • The setae, or tiny hairs on the limbs could be worn or nearly gone
  • Cloudy eye stalks
  • Grey, muted coloration on the body

The molting process is fascinating and may seem like it takes forever, but you will have to resist the urge to check on it because handling a molting hermit crab could cause severe injury. Be patient, and as long as you don’t smell a rotting odor, your pet will emerge looking brand new.

How To Treat A Foaming Hermit Crab

While hermit crab foaming doesn’t happen often, there are a few things you may be able to do to help it. First, you should refrain from picking it up in case the hermit crab is severely injured. 

Check to see what color the bubbles are before doing anything. If the bubbles are clear or white, chances are your hermit crab is dehydrated, overheated, or experiencing shell irritation. 

Offer it clean, fresh, and saltwater to see if your hermit crab only needs a nice, relaxing soak. Also, check the humidity and heat levels and adjust accordingly. 

If you know your hermit crab is suffering from dehydration or overheating, you can carefully pick it up and set it in one of the baths, or you can mist it with distilled water. 

A hermit crab that is foaming brown, or produces a bad odor is injured, or stressed, and should not be moved at all. Try to keep the other hermit crabs away from it, remove anything that could be causing stress, and make sure the crabitat is comfortable. Other than that, all you can do is wait or contact your vet, although they may not be able to do anything. 

How To Prevent Hermit Crab Foaming

When a hermit crab is foaming because of PPS, there isn’t much you can do except to make sure you have a comfortable environment, and wait it out. If you only have one hermit crab, try to get one or two more because it may just be incredibly lonely.

By providing a great environment for your hermit crabs, you will do all you can to prevent foaming. Keeping the tank sufficiently warm and humid will keep them from drying out and staying healthy. Making sure you have both saline and freshwater will allow them to soak when they feel thirsty or dry, and they can wash away any irritation. 

How Long Will Hermit Crabs Continue To Make Bubbles?

When you remove the stressors or fix what was causing the bubbles, your hermit crab should stop foaming pretty quickly. If it’s injured or has fallen very ill, it may take longer. Unfortunately, we don’t have a clear amount of time it should take. 

If the bubbling is severe or starts to smell bad, all you can really do is try and make it as comfortable as possible. Most likely, it is not going to survive much longer.  


What is that little bubble on my hermit crab’s leg?

Stress, fighting, or other injuries can cause a hermit crab to lose a claw or leg. While this surely is painful, hermit crabs can regenerate limbs. When they start to prepare for a molt, they can create a small, translucent sac on the injured limb.

This is the start of the regeneration process. The newly growing limb will be small, and possibly soft when it first molts, but after a few successful moltings, the limb will be completely regrown.

Can I spray my hermit crab with tap water?

Never use tap water for your hermit crab. You shouldn’t even clean dishes or toys in tap water because chlorine, and other additives to the water can be harmful or even fatal. Use distilled water for cleaning, bathing, and drinking.

Hermit crabs also need saltwater but don’t use table salt to make saltwater. Use a quality marine salt and mix it according to the directions for your saltwater bath for hermit crabs.

How do you save a sick hermit crab?

When you have a sick hermit crab, the best thing you can do is isolate it from any other hermits, but don’t pick it up. Move the others or put a barrier between the sick and healthy crabs. Offer it clean water, fresh food, and a non stressful environment.

You can also contact your local vet to see what else you can do.

Wrapping It Up

Hermit crabs can foam up just because they are breathing, but it’s best to keep a very close eye on them if they do start foaming. A healthy hermit crab in a well maintained environment most likely won’t need to do any bubbling or foaming.

Foaming can be an indication of fast breathing due to injury or stress, an attempt to moisten its gills, or a way to remove a shell irritation. Sometimes simple adjustments to the enclosure can remedy the foaming.

Brown foaming, or foam accompanied by a strong odor are more worrisome and may lead to the hermit crab’s demise. When this happens you can try to heal the hermit crab, but it may not help. Hopefully, you never have to experience any of these conditions, and your hermit crab will live a long and happy life with you.

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