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do hermit crabs have brains?

Are Hermit Crabs Intelligent?

Intelligence can be difficult to assess, especially in non-verbal animals with limited body language. So, it’s likely that you’ve wondered if hermit crabs are smart.

‘Intelligent’ may not be the most accurate way to describe hermit crabs, but they aren’t dumb. Hermit crabs are basic creatures with functional brains, so they can’t solve puzzles or remember faces.

They can detect/recall pain and recognize the smell of their own dead over other animals. Hermit crabs pick their shells based on preference and can determine which shells will best meet their needs.

So, hermit crabs are intelligent, it seems, but only within their own metric. Their minds have evolved sufficiently to meet their day-to-day survival requirements.

Do Hermit Crabs Have Brains?

To understand hermit crabs’ intelligence, we need to better understand their brain. In contrast to other animals and humans, they hardly seem like brains.

Science knows little about the anatomy and structure of hermit crabs’ brains. Much of what’s assumed is based on data about crabs. Specifically, this data comes from brachyuran crabs, which are true crabs with a thick outer shell and a short tail.

How Big Is A Hermit Crab’s Brain?

A hermit crab’s brain is so small that a naked human eye will struggle to see it.

That’s because the hermit crab’s brain is a sparse bundle of nerves, lacking the lobes and sections you’ll find in other animals or humans. 

Hermit Crab Brain Structure

Hermit crabs’ brains have a similar function to standard brains.

They’re responsible for transmitting and interpreting signals sent and received throughout the hermit crab. This helps them understand and navigate their surroundings.

However, hermit crabs have a simple and primitive setup for their nervous system.

In contrast, human brains are largely composed of tissue connected to other parts of the body by nerves. These nerves pick up signals, which provide information about the world around us.

Hermit crab brains are composed mostly of a nerve cord found on the underside. The brain is connected to other body parts through nerve bundles called ganglia. Ganglia act as a relay system to send a message from the sensory organs to the brain.

A hermit crab’s ganglia are similar to those found throughout the human nervous system, which is the case in what they’re made of and how they function. However, hermit crabs have far fewer ganglia.

How Intelligent Is A Hermit Crab?

A hermit crab’s intelligence is largely unstudied. However, because of their simple brains, many assume that hermit crabs aren’t smart.

Their limited range of intelligence could even appear dumb, as they can’t solve puzzles or be taught tricks. They’ll spend most of their lives eating, walking, and digging.

We can look for signs of intelligence in hermit crabs’ ability to navigate their environment. Here, they show certain behaviors and instincts that can be interpreted as a form of intelligence.

Shell Preference

Hermit crabs are famous for how they change their shells. As hermit crabs grow, they’ll swap their shells for a larger size, continuing until they’re fully grown.

While you may expect the hermit crab to be satisfied with its new home, that’s not the case. Even fully-grown hermit crabs will continue swapping out their shells, and there’s no schedule for this shell swap.

According to Animal Behavior, hermit crabs are picky about their shells. Hermit crabs will pick one type of shell over another and remain consistent in that choice.

Rather than choosing whichever shell is nearby or size-appropriate, a hermit crab will be selective. It’ll opt for a certain shell type, with few exceptions.

Additionally, hermit crabs know which shells are more structurally sound than others. In the Journal of Shellfish Research, hermit crabs were presented with different shells with varying levels of damage.

The hermit crabs were exposed to isolation and stimuli that mimicked predators. In all experiments, the hermit crabs always preferred the undamaged shell.

Combined, these two studies suggest that hermit crabs can differentiate one shell from another. Also, they know which shells give them a better chance of survival. This indicates that hermit crabs may be making a choice, which can be a marker of intelligence.

how big is a hermit crab's brain?

Smell Their Dead

According to Ecology and Evolution, hermit crabs can smell their dead. Most importantly, they can differentiate them from other smells of decay and react accordingly.

When hermit crabs realize a fellow member of their species has died nearby, they’ll rush to the site. This ability to smell their dead is an advantage.

Because terrestrial hermit crabs need to find the perfect fit, free shells are always in high demand. When a hermit crab dies, its shell is available.

This shows an amazing sense of smell and indicates that hermit crabs are opportunistic. That’s intelligence outside the need to avoid predators, obtain food, or ensure protection.

This is supported by BMC Neuroscience, where scientists discovered that a large part of a terrestrial crab’s brain structure is dedicated to identifying smells.

Remember And Adapt To Pain

There’s been a long-standing debate about whether crustaceans, like crabs and lobsters, can feel pain.

However, a recent study published in Animal Behavior found that hermit crabs can feel pain. In fact, they’ll recall pain and act accordingly following the negative experience.

To perform this study, a group of hermit crabs was given small electric shocks within their shells. They were then given the option to move into new, empty shells.

Shocked hermit crabs were the only ones who moved outside their shells, proving that they could feel pain. More interestingly, the shocked hermit crabs moved into their new shells differently than those who weren’t shocked.

They approached the shell much faster and investigated it for a shorter time. This implies that the hermit crab remembered the previous experience of being shocked.

Also, this suggests a problem-solving approach from hermit crabs due to quickly retreating to a new haven, perhaps understanding the urgency.  

This study also supports the theory that hermit crabs have preferred shells. Hermit crabs in their preferred shells were less likely to evacuate their current shells.

hermit crab intelligence

Do Hermit Crabs Make Smart Pets?

Many owners report their pets displaying more traditionally intelligent behaviors, such as:

  • Recognizing the sound of an owner’s voice.
  • Learn to come over with the promise of food.
  • Responding to sounds, such as chirping back when their owners chirp at them.

There’s little scientific evidence to support this directly.

Can You Train A Hermit Crab?

With reports from owners, it’s suggested that pet hermit crabs can undergo very basic training. However, they’re not intelligent enough to learn advanced tricks.

Instead, you can ‘train’ a hermit crab by reinforcing certain habits with the reward of food.

In this way, your hermit crab will eventually start to perform that action regularly. Is that because it’s smart enough to make the connection, or is it following food with blind intention?

Hermit crabs may recognize your preferred feeding times or learn to eat from your hand.

Can Hermit Crabs Recognize Their Owners?

There’s no scientific proof that hermit crabs can recognize or remember faces.

However, it’s possible that hermit crabs can learn your tone of voice. Their ability to detect sound at close range allows hermit crabs to respond to danger. After all, their natural predators aren’t always quiet.

A hermit crab may respond to the sound of an owner speaking. If hermit crabs are well settled and rewarded with food upon hearing that sound, they may react positively.

Hermit crabs may not be smart the same way that humans are smart. However, they show a type of intelligence that allows them to adapt and survive.

From a scientific perspective, hermit crabs use their limited brain function to avoid pain, remember dangers, and seek better shells.