Animal cognition is a truly fascinating subject. Many household pets have been subjected to neurological tests to assess their thinking prowess and memory. It may surprise you to learn that hermit crabs have also experienced such experimentation.
Science has proven that hermit crabs hold memories. Hermit crabs will rarely eat the same food twice in 24 hours. They recall previously occupied and unsuitable shells and recollect painful experiences. Hermit crabs also seem to memorize territory, in addition to remembering friendly or antagonist tankmates.
Hermit crabs are primarily guided by survival instinct. All the same, it appears that they recollect both good and bad experiences.
What Do Hermit Crabs Remember?
Before assessing the memory of hermit crabs, they should discuss the brain of these animals. As hermit crabs are so tiny, you would be forgiven for assuming that, like a starfish, they have no such organ. You’d be half-right.
The neurological architecture of hermit crabs is comparable to earthworms. As per BMC Neuroscience, hermit crabs rely on sensory organs over cognitive thought. Hermit crabs have a primitive sensory system, comprising of a clutch of ganglia attached to nerve cords.
Hermit crabs can see, though this is not their primary sense. Instead, hermit crabs rely on tiny hairs on their legs. These detect vibrations, which help them to locate sounds and respond to saltwater to create a sense of smell.
This suggests that hermit crabs are creatures of pure instinct, living exclusively in the moment. This is not strictly true. While the precise length of the hermit crab memory span is unknown, they can recollect particular events and happenings.
Perhaps the most pertinent evidence of hermit crab memory is in the diet. In the wild, hermit crabs are omnivorous scavengers. They will eat anything available. This means that hermit crabs enjoy a wide and varied array of nourishment.
As a result of this, as per Animal Behavior, hermit crabs will avoid eating the same food twice in 24 hours. This needs to be factored into the diet you offer your crabs. There is much more to feeding hermit crabs than just buying a box of pellets from a pet store.
Offer your hermit crabs a different range of protein- and calcium-rich foods each day. This way, your hermit crabs will remain engaged with their food. Fresh fruits and vegetables are always a winner, alongside nuts and small, chopped servings of meat and fish.
Alongside sustenance, shell availability is among the most pivotal element of hermit crab care. In many respects, hermit crabs take the opposite approach to choosing shells as they do food.
According to the Journal of Experimental Marine Biology and Ecology, hermit crabs select shells that remind them of a previous shelter. This means choosing a shell of equitable weight and mobility to what has been used before.
Hermit crabs change shells for many reasons. In an emergency, any shell will do. Some hermit crabs use sponges or trash as an emergency shelter. Eventually, though, hermit crabs seek something comfortingly familiar.
Applied Animal Behavior Science confirms that hermit crabs feel – and recall – pain. Hermit crabs in a laboratory were subjected to electric shocks within their shell. The hermit crabs responded to this unwelcome stimulus. Some attempted to escape their enclosure.
What is interesting is the trade-off that hermit crabs consider when experiencing pain. This experiment found that some hermit crabs tolerated more electric shocks than others before leaving their shells. The hermit crabs that enjoyed superior shells were more resilient.
After the event, some of the hermit crabs returned to their shells. This suggests they considered the pain a worthwhile trade for such a reliable shelter.
Other hermit crabs that had inferior shells investigated these former homes then walked away. They remembered the electric shocks that were administered within the shell. Upon reflection, they decided the shell was not worth the discomfort it caused.
Hermit crabs also avoid food that previously made them sick. The Biological Bulletin describes an experiment in which beef was injected with lithium chloride. Hermit crabs involved in a trial that ate this beef rejected it in the future. This suggests hermit crabs remember health concerns caused by food.
Wild hermit crabs live in colonies of up to 100. This means that the pecking order will need to be quickly established. As territorial animals, hermit crabs establish dominant and submissive roles to avoid unnecessary conflict.
Hermit crabs do not struggle to remember their place in this hierarchy. Ethology confirms that hermit crabs can recall a dominant rival after just 30 minutes of exposure. This memory is retained for at least 4 days after separation.
This does not need to be a negative experience for hermit crabs. If one hermit crab takes on the status of ‘protector’, others may gravitate toward it. It is not unheard of for hermit crabs to seek out missing tankmates during molting or following death.
If hermit crabs make a later play for dominance, it does not mean they have forgotten their previous defeat. It merely suggests that alpha status is fluid among hermit crabs.
With every molt, hermit crabs grow bigger and stronger. New shells can also embolden hermit crabs. The previously docile hermit crab may decide it has had enough of being pushed around and now wants to take up status as head of the habitat.
Bossy tankmates are a mild concern compared to external predators for hermit crabs. Hermit crabs remember the location and behavior of predator wildlife. As a result, hermit crabs adjust their behavior accordingly.
As per Biology Letters, shell selection will be keenly influenced by the presence of predators. If hermit crabs recall that an enemy is in the vicinity, they choose inconspicuous shells. If the shell is robust, hermit crabs spend more time within this protective shield.
Chemical Communication in Crustaceans confirms that hermit crabs also rely on scent to avoid predators. Alas, if a hermit crab is hungry enough, this drive overpowers the desire to stay safe. Hermit crabs do not place as much stock in memory as they perhaps should.
As per Biological Invasions, invasive species are faster learners than indigenous wildlife when it comes to recalling predators. This is presumably due to necessity.
If hermit crabs find themselves displaced, there is no room for complacency. They need to rapidly memorize the dangers associated with territory. This also explains why hermit crabs are initially anxious upon entering captivity before growing in confidence.
Hermit crabs do not recognize humans by sight, as far as we are aware. This does not mean that hermit crabs do not remember their owners, though. The keen sense of smell of hermit crabs means that they recall our distinctive scent, especially when handled.
Put yourself in the shoes of a hermit crab. Humans must be frightening to these animals. We dwarf them in size, can easily pick them up, and speak in loud, booming voices. This, naturally, encourages hermit crabs to shy away from human contact initially.
It is possible to build the trust of a hermit crab. Like most animals, food is the fastest way to a hermit crab’s heart. By providing a snack alongside handling, your hermit crabs will remember you as a source of pleasure.
Your hermit crabs will not react the same way to strangers, though. Once you have bonded with hermit crabs, they will crawl in your hand without concern. Try to get it to do the same with a stranger, though. The crabs will likely chirp and retreat into their shell.
Hermit crabs enjoy exploring new terrain. As natural scavengers, new territory provides a wealth of unique foraging opportunities for hermit crabs. They never know where they may locate a new food source.
Despite this, hermit crabs will always eventually return to familiar territory. Marine Behavior and Physiology confirms that displaced hermit crabs make their way back toward the sea. While this could be instinct, captive hermit crab behavior suggests this is not the case.
Watch how your hermit crabs act in a tank. Each crab will have its own assigned territory. One may show a preference for a particular rock; others will always burrow in the same spot. This suggests that hermit crabs remember safe and previously claimed terrain.
You will also likely that hermit crabs will cease playing with toys after a spell. Hermit crabs enjoy novelty in all things, not just food. Your hermit crabs remember everything about their habitat. While this can be comforting, it can also make for a dull life.
After deep cleaning a hermit crab tank, rearrange the layout. You can recycle toys and peripherals, as long as they have been cleaned. Just place them in different locations. This inspires hermit crabs to explore again. They do not remember their habitat looking like this.
Hermit crabs clearly retain memories. This means you have a duty as a keeper of hermit crabs to provide positive life experiences.