Why Do Crabs Bubble at the Mouth? 7 Causes of Bubbling

Crabs are some of the most fascinating aquatic pets you can find, with lots of unusual behaviors that baffle their owners. For example, many people wonder why do crabs bubble at the mouth and if this behavior is normal.

Unfortunately, as people have only recently started keeping these crustaceans as pets, there are many things that can confuse even experienced crab owners. Bubbling and foaming are some of these occurrences.

So, why do crabs bubble at the mouth, and is this behavior a sign that there’s something wrong with your pet?

Let’s find out!

Why Do Crabs Bubble at the Mouth?

There are many types of crabs, such as:

• Fully aquatic crabs, such as panther crabs and blue crabs.
• Semi-terrestrial or intertidal crabs, including fiddler crabs, hermit crabs, vampire crabs, rainbow crabs, and red claw crabs.
• Terrestrial crabs, such as marble crabs, coconut crabs, or Thai devil crabs. 

All types of crabs might experience bubbling, especially when on land. This is a behavior most crab owners will notice at least once. But, what’s causing it?

There are 7 possible reasons why do crabs bubble at the mouth. I’ll go over all of them.

1. Breathing

In most cases, crabs produce bubbles due to the way they breathe (also known as a buccal pump ), especially when they are on land.

All types of crabs have gills. Yes, even the terrestrial ones, although a lot of them will also have a pair of modified lungs.

Just like in humans and other terrestrial creatures, crabs breathe in oxygen and breathe out carbon dioxide. As the air they’ve filtrated goes through their lungs, it will cause bubbles. This is the same thing that happens when you’re blowing bubbles inside the swimming pool!

2. Dehydration

If you notice your crab bubbling at the mouth while on land, chances are it is to save itself from dehydration.

Even intertidal and terrestrial crabs need to keep their gills moist to survive. The easiest way to do so is by bubbling. 

On such occasions, this strange behavior is to draw water to the body. This will ensure the gills of crabs are moist enough to keep on circulating air. Without moist gills, your crab might suffocate.

If you notice your crab bubbling while on land, make sure to check the humidity levels. They should be at least 70%, but 75 – 85% is ideal. 

Also, give your crab a water source that’s easy to reach. Maybe your pet is thirsty. This is especially the case if you notice brown bubbles. 

3. Stress

Stress is another common reason why a crab might be bubbling. For example, if you notice your hermit crab bubbling for days even though all other things seem to be in order, chances are it is stressed out as it’s lonely.

Hermit crabs are social creatures that live in large colonies. If you move them to a new home without giving them proper company, they might bubble as a result of stress.

Another stressful situation is overheating. If your crab has frequent land excursions but the land temperature is too high, a crab might bubble to cool itself down.

Too much handling can also cause stress. Don’t handle your crab for too long. If you’re worried about tank maintenance, don’t be. There are ways to keep your aquarium clean without touching the animals that live in it with a human hand.

4. Irritation

While you might think you have a crazy crab that has decided to bubble, maybe your pet feels irritated.

For example, another reason behind brown bubbles is if there is too much dirt and debris in the surrounding water. This dirt will enter the exoskeleton, so the crab will produce a flow of water and bubbles to get all the particles out of its gills. 

While your crab keeps itself clean in regular condition by using its legs (or rather, small appendages), if the space is too tight or too dirty, it might exhibit hygiene problems. This will usually be noticeable to the naked eye. 

Remember, it isn’t enough to know how to keep the tank glass crystal clear. You need to clean the water regularly, as well.

Another reason behind irritation might be brackish water. While some crabs require brackish water to breed, most are rather sensitive to salt. This can not only lead to irritation but also death.

5. Acclimation Issues

If you’ve just added your crab to its new home with good conditions, maybe it’s just having some acclimation issues.  

You can never be too certain about the conditions crabs were kept in, especially if you’ve bought them from pet stores. 

Keep a close eye on your new crab. If the bubbling stops after a few days, it simply needs some time to get used to its new environment. However, if the bubbling persists, check your parameters. Maybe there’s something you’ve missed.

6. Molting Process 

If you notice your crab bubbling, take a closer look. Maybe it’s just entering the molting phase.

For example, when you see a fiddler crab molting, you might notice a tiny, gray bubble on its shell. This isn’t an air bubble. Rather, your crab is producing a fat and water reserve that it can access while it’s molting.

If this is the first time you’re experiencing molting, these are a few signs to look for:

• Lethargy,
• Change in appetite,
• The body becomes gray,
• Excessive digging,
• Restlessness.

If you keep other crustaceans, such as bumble bee shrimp, you might be familiar with this behavior.

7. Injury

Finally, your crab might be bubbling because it is injured.

Injuries are rather common in community tanks. Either by accident or due to rivalry, crabs might hurt each other. Just like humans breathe harder when they are hurt, so do crabs. This heavy breathing will cause bubbles. 

Bubbles from injured crabs are usually brown in color. Unfortunately, if this discoloration is followed by a foul smell, chances are your crab is taking its final breath.

Is It Normal for Crabs to Bubble?

Now that you know why crabs bubble, you’re probably wondering whether you should be concerned.

In general, crab foaming and bubbling is pretty normal behavior. Lots of crab species will bubble rather frequently. As mentioned, this is a way to keep their gills moist and is an entirely natural process.

However, if you notice your crab is bubbling for an extended period of time or that the bubbles have changed in color, this is a negative sign. Usually, this means your little crustacean is dehydrated or stressed out.

The foul smell is the worst symptom you might run into. It is always a sign that something is terribly wrong with your crab. 

The Final Word

Now you know why do crabs bubble at the mouth. This is pretty normal behavior for most crabs and is simply a way crabs adjust to environmental changes and dry land. 

However, it’s a red flag if you notice your crab is bubbling for a long time.

If this happens, you should check the tank conditions and make sure all the parameters, such as water temperature and humidity levels, are okay. Also, you should stop handling your crab too often, as this can further stress it out. 

Finally, make sure your crabs have plenty of reservoirs of water. As bubbling might be a sign of dehydration, you want to make sure your little pet has a readily available water source. 

Keep in mind that a crab might keep on bubbling until it recovers. Don’t get discouraged if this behavior continues for a while, but keep a close eye on your little pet. 

With proper care, you can enjoy the company of your crab for many years to come.