do hermit crabs have brains?

Are Hermit Crabs Intelligent?

Intelligence can be difficult to measure, especially in nonverbal animals with limited body language, like hermit crabs. As an owner, you’ve probably wondered if hermies are smart. Overall, intelligent may not be the most accurate term to describe hermit crabs, but they certainly aren’t dumb.

Hermit crabs are basic creatures with simple brains. They won’t solve puzzles or remember faces. However, hermit crabs do have a kind of intelligence. This is shown in their ability to detect and remember 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 are most structurally sound.

So, hermit crabs are intelligent, it seems, but only within their own metric. Science is still uncertain about the smarts of hermit crabs. However, owners have reported that hermit crabs do show more traditionally intelligent traits. They can learn their owner’s voice, respond to sounds, and accept elementary training.

Do Hermit Crabs Have Brains?

To understand a hermit crab’s intelligence, we need to understand their brains. Indeed, hermit crabs do have brains. However, in contrast to other animals and humans, they hardly seem like brains at all. Science knows little about the anatomy and structure of hermit crabs’ brains. Most of what is assumed is taken from data regarding other crabs.

Specifically, this data comes from brachyuran crabs. Brachyuran crabs are the most standard form of a crab. These crabs have a thick outer shell and a short tail. Unlike hermit crabs, these kinds are scientifically considered to be true crabs. Even still, like the true crab, hermit crabs do have brains.

How Big Is A Hermit Crab’s Brain?

The size of a hermit crab’s brain is tiny. In fact, it’s so small that a naked human eye will struggle to see it. That’s because the hermit crab brain is nothing more than a sparse bundle of nerves. It lacks the lobes and sections that you’ll find in other animals or humans. 

Hermit Crab Brain Structure

Hermit crabs’ brains have a similar function to all standard brains. They’re responsible for transmitting and interpreting signals sent and received throughout the hermit crab. This helps the animal to understand and navigate its surroundings. However, hermit crabs diverge at one crucial point. They have a simple and primitive setup for their nervous system.

In contrast, human brains are largely composed of tissue. This is connected to other parts of the body by nerves. These nerves pick up signals, which give information to the brain about the world around us. What we taste, what the temperature is like, and if we’re hungry are all information that the brain receives.

Hermit crab brains, on the other hand, are composed mostly of a nerve cord. This is found on the hermit crab’s underside. The brain is connected to other parts of the body 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 the ganglia found throughout the human nervous system. This is the case in what they are made of and how they function. However, unlike humans, hermit crabs have far fewer ganglia.

Hermit crabs do have a brain, but it lacks complexity. It’s mostly dominated by its nerve cord, without the extra fanfare of a larger or more intricate brain. Because of this, they rely on their nerve cord, which is connected to fewer ganglia (or lines of communication). The signals that are transmitted and received throughout the hermit crabs’ body are basic.

How Intelligent Is A Hermit Crab?

A hermit crab’s intelligence is largely unstudied. However, because of their simple brains, many people assume that hermit crabs are not smart. In fact, their limited range of intelligence could even appear dumb. They can’t solve puzzles or be taught tricks. They will spend the majority of their lives eating, walking around, and digging.

Nonetheless, we can look for signs of intelligence in a hermit crab’s ability to navigate its environment. Here, they do show peculiar behaviors and instincts. These may be interpretable as a real form of intelligence.

Hermit Crabs Have A Shell Preference

Hermit crabs are most famous for how they change their shells. As a hermie grows, it will swap out its shell for a larger size, continuing until it’s 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 for no apparent reason. There’s also no set schedule for this shell-swap.

Instead, it seems to be a preference. According to Animal Behavior, hermit crabs are picky about the shells they choose to support this idea. Hermit crabs will pick one species 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 will always opt for a certain shell type, with a few rare 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 then exposed to isolation and stimuli that mimicked predators. In all experiments, the hermit crabs always preferred the undamaged shell.

When combined, these two studies suggest that hermit crabs can differentiate one shell from another. On top of that, they know which shells give them a better chance of survival. This indicates that hermit crabs may be making, to an extent, a choice. That can be a marker of intelligence.

how big is a hermit crab's brain?

Hermit Crabs Can Smell Their Dead

According to Ecology and Evolution, hermit crabs have the ability to smell their dead. Most importantly, they can differentiate this from other smells of decay and react to this knowledge.

When hermit crabs realize a fellow member of their species has died nearby, they tend to rush the site. This ability to sniff out their dead is an advantage. Because terrestrial hermit crabs need to find the perfect fit, free shells are always in high demand. When a hermie dies, that means that its shell is free for the taking.

This not only shows an impressive sense of smell. It indicates that hermit crabs know how to be 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 sniffing out smells. This improves their ability to detect these moments of opportunity at a great distance.

Hermit Crabs Can Remember And Adapt To Pain

There’s been a long-standing debate on whether or not crustaceans, like crabs and lobsters, can feel pain. However, a recent study published in Animal Behavior shows that hermit crabs can feel pain. In fact, they’ll even remember it and act accordingly after the experience.

To perform this study, a group of hermit crabs was given small electric shocks within their shells. They were then given a choice to move into new, empty shells. Shocked hermit crabs were the only ones who moved outside of their shells. This proves that hermit crabs can feel pain. More interestingly, the group of shocked hermit crabs moved into their new shells differently than those who were not shocked.

They approached the shell much faster and investigated the shell for a shorter period of time. This implies that the hermit crab remembered the previous experience of being shocked. This also suggests a problem-solving approach from hermit crabs due to quickly retreating to a new haven, perhaps understanding the urgency.  

Notably, this study also supports the theory that hermit crabs have preferred shells. Hermit crabs that were 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. For example, they may be able to:

  • Recognize the sound of their owner’s voices
  • Learn their own name and come when called, usually with the promise of food.
  • Respond to sounds, such as chirping back when their owners chirp at them

With that said, there’s little to no scientific evidence to support this directly. That may be due to a lack of demand, as mirrored in the lacking data on hermit crab brains. Studying hermit crabs, as of now, has not been that necessary.

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’ the 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 simply following food with blind intention? That’s up for debate.

For example, it may recognize feeding times based on your presence. Likewise, the hermit crab may learn to eat from your hand. Intelligent or not, these basic actions can still make a pet hermit crab very endearing.

Can Hermit Crabs Recognize Their Owners?

There’s no scientific backing to suggest that hermit crabs can recognize or remember faces. Even among hermit crab owners, it appears that hermies do not show any indication of this.

However, it’s suggested that hermit crabs can learn your tone of voice. This ability to detect sound at close range allows hermit crabs to respond to danger in the wild. After all, its natural predators aren’t always quiet.

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

Hermit Crabs Are Smart In Their Own Right

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

From a scientific perspective, they use their limited brain function to avoid pain, remember dangers, and seek better shells. From an owner’s perspective, they’re simple but endearing creatures. This allows them to show off their limited intelligence in subtle but meaningful ways.