Home » How Do Hermit Crabs Breathe? [Lungs vs. Gills]
can hermit crabs breathe underwater?

How Do Hermit Crabs Breathe? [Lungs vs. Gills]

Hermit crabs primarily breathe through gills, whether they live on land or underwater. Terrestrial hermit crabs have also evolved to develop a single branchiostegal lung. A hermit crab’s gills must be kept moist to enable easy breathing.

Land-dwelling hermit crabs must live in humid conditions to breathe easily. Avoid allowing the humidity in a hermit crab enclosure to drop below 80%, which increases the risk of suffocation. Be aware that terrestrial hermit crabs can’t breathe underwater.

Marine hermit crabs can breathe indefinitely underwater, but their gills dry out quickly on dry land. If you keep aquatic hermit crabs, never remove them from the water for more than a few minutes.

Hermit crabs are prone to suffocation if kept in inappropriate conditions, and this is a common cause of mortality in captive hermit crabs.

Does a Hermit Crab Have Lungs or Gills?

All hermit crabs, whether they live on land or in the water, have gills.

A terrestrial hermit crab must keep its gills damp. If a hermit crab lives in arid conditions, its gills will start to scar and close, making breathing increasingly difficult.

Despite their reliance on gills, terrestrial hermit crabs have also evolved and developed lungs. As explained by Arthropod Structure and Development, most hermit crabs have developed a branchiostegal lung over the more familiar abdominal lung.

This is because a branchiostegal lung is small and thin, making it easier to absorb air taken in by the gills and pass it to the bloodstream, especially when an external shell covers most of a hermit crab’s body.

Gills and lungs work in tandem to enable hermit crabs to breathe. Both are equally important for access to air, so you must provide your pets with an appropriate habitat to ensure maximum performance.  

Do Hermit Crabs Need Oxygen to Breathe?

According to Comparative Biochemistry and Physiology, oxygen is vital for marine hermit crabs to breathe, while terrestrial hermit crabs rely more on carbon dioxide for air.

Land-dwelling hermit crabs can spend a little time in the ocean. In the wild, hermit crabs wait for a high tide and submerge themselves in salt water for a short while. Equally, marine hermit crabs will spend a little time on a beachfront seeking food.

One thing is consistent in both types of hermit crab – an appropriate environment is critical to prevent suffocation. Land hermit crabs can’t spend excessive time underwater, and marine hermit crabs can’t spend too much time on dry land.

can hermit crabs drown?

Warning Signs That a Hermit Crab is Suffocating

Suffocation is a common but avoidable cause of death in captive hermit crabs. If you wish to care for them, you must understand the warning signs that your hermit crabs are struggling for air.

Symptoms of suffocation in hermit crabs include:

  • Uncharacteristic lethargy and a reluctance to climb or explore.
  • Failing to burrow under the substrate, especially during daylight hours.
  • Excessive hiding.
  • Attempting to leave the shell for any reason other than upgrading to a replacement vessel.
  • Shedding of claws or legs.
  • Refusing to eat.
  • Fading of the skin tone to a dull, listless gray.

If you spot any warning signs of suffocation, consider what may be awry and take action. It takes a while for hermit crabs to suffocate, but it’s a slow and unpleasant way for the animal to die. If you acknowledge the risk early, you can prevent this outcome.

Some of these symptoms are similar to an impending molt; the core difference is that a hermit crab that prepares to molt will eat more than usual and spend more time digging, not less.

How Do Land Hermit Crabs Breathe?

Terrestrial hermit crabs hail from tropical conditions, which means they rely upon humid conditions to breathe freely. Humidity and carbon dioxide are intrinsically linked, so the higher the humidity in an enclosure, the easier it is for land hermit crabs to breathe.

Captive hermit crabs must live within an airtight enclosure, which ensures humid air is drawn through the gills into the blood via the branchiostegal lung.

Get in a hygrometer for your hermit crab habitat to ensure that humidity levels remain appropriate. 80% is considered the optimum level of humidity. Any less and your pet hermit crabs will gasp for air, but too much moisture can encourage mold growth on the walls of a tank.

You can take steps to increase the humidity in a hermit crab tank. Consider the following actions:

Hermit crabs that can breathe easily will be happy and healthy, growing active and contentedly exploring their surroundings from the moment the sun goes down.

How Do Hermit Crabs Breathe Under Sand?

Hermit crabs love to burrow under their substrate. Wild hermit crabs spend most of the day buried under sand, hiding from predators and avoiding the sun’s heat. Captive hermit crabs often sleep under the sand and hide under their substrate while molting or stressed.

You may be concerned that burrowing under the sand is a suffocation risk, but this isn’t the case if you provide an appropriate substrate. Playground sand is safe, as is coconut soil or creature soil purchased from an exotic pet store.

These substrates are safe for burrowing as they’re fine, and Hermit crabs can dig a tunnel that creates a direct line to air and oxygen. An appropriate substrate will not collapse and lead to suffocation, ensuring that your hermit crabs can breathe while they enjoy privacy.

You can tell if a substrate will be safe for hermit crabs by attempting to build a sandcastle (or an equivalent if using soil). If the substrate is too brittle to hold such a shape, it risks suffocating your hermit crabs. If the sandcastle holds firm, it is safe to use as a substrate.

To be increasingly cautious, wet the substrate before building the sandcastle and ensure this doesn’t alter the texture. Wet potting soil, for example, turns to mud and restricts the ability to breathe. As hermit crabs spill water in an enclosure, this is a cause for concern.

How Do Hermit Crabs Breathe Underwater?

Land hermit crabs don’t breathe underwater; they hold their breath while submerged. While terrestrial hermit crabs enjoy spending time doused in water to bathe and fill their shells with drinking water, they can’t do so indefinitely.

You won’t always be able to supervise your hermit crabs’ time underwater. As they’re naturally nocturnal, they may bathe while you are asleep. Minimize the risk of drowning with these precautions:

  • Keep bodies of water small. Hermit crabs don’t swim, so they don’t need expansive pools of water.
  • Avoid overfilling baths and use vessels with shallow edges. Bathing water must only be deep enough to submerge a hermit crab’s body.
  • Ensure your hermit crabs can quickly get in and out of water. Ramps are the best way to achieve this, but you could also use nets.
  • Encourage your hermit crabs to bathe while you are active, reducing the likelihood of them spending unsupervised time underwater.
  • Clean the habitat regularly to minimize the risk of mite infestations, which will drive hermit crabs to spend more time in the water.

Most hermit crabs can hold their breath for around 20–30 minutes. If your hermit crab is underwater for longer, it may grow disoriented and dizzy.

Drowning is a constant risk for land hermit crabs that must be managed.

how long can hermit crabs stay underwater?

How Do Marine Hermit Crabs Breathe?

Marine hermit crabs have an appendage at the underside of the mouth near the claws, known as the scaphognathite.

The scaphognathite draws water to the gills, and vital oxygen is extracted from this water and passed to the bloodstream. As aquatic hermit crabs rely on oxygen rather than carbon dioxide, the latter is expelled through the mouth.

In theory, aquatic hermit crabs are easier to care for and less likely to suffocate than their terrestrial counterparts. As long as they’re kept underwater, they’ll keep breathing, and drowning isn’t a concern.

However, like terrestrial hermit crabs, marine hermit crabs need specific conditions to breathe easily. Factors to take under advisement include:

  • Use saline water from a reputable seller; avoid tap water that contains chlorine or heavy metals.
  • Water pH should not drop below 8.0 or exceed 8.4.
  • Water gravity should fall between 1.021 and 1.028.
  • Nitrate levels should not exceed 10 parts per milligram.
  • Don’t allow the water temperature to drop below 72OF or exceed 78OF.

Stick to these guidelines, and your marine hermit crabs will breathe freely and easily.

How Long Can Hermit Crabs Breathe Underwater?

Marine hermit crabs can breathe indefinitely underwater if their environmental needs are met.

Unlike in the wild, captive marine hermit crabs will be happy to remain submerged in water 24/7. There’s no need for them to explore dry land.

Can Hermit Crabs Breathe Out of Water?

Marine hermit crabs can breathe outside the water as long as their gills remain moist. When these gills dry out, the hermit crab will struggle to breathe.

This happens much faster in marine hermit crabs than in their land-based counterparts. As a result, removing aquatic hermit crabs from water for longer than a few minutes is inadvisable.

The only occasion you need to do this is while an aquarium is cleaned. This can take 24 hours to complete, so you’ll always need a second tank to keep your pets in during the process.

While it would be ideal to have two aquariums running at all times, that’s unrealistic, as it’ll be noisy and expensive in terms of power consumption. You can keep your hermit crabs in a basic water feature while you prepare a second tank.

Whether you are using a bathtub, sink, or goldfish bowl, the usual caveats apply to this temporary home. The water should be between 72–82OF, offer a pH between 8.1 and 8.4, and a salinity of 1.021–1.028 – and never use table salt for this, as iodine will kill your hermit crabs.