The hard problem of consciousness becomes even greater when I consider the proprioception, or awareness of position, movement and force of the body of a hermit crab. Without a shell, the spatial awareness and placement of its limbs etc is one thing, but by inhabiting a “virtual body” integral to its survival, does proprioception extend to include a mass for which its sensory mechanisms end at its soft and hard exoskeletons? Does a hermit crab’s sense of self expand to include the shell of another organism?

Hermit crabs source their embodied homes from the discarded shells of gastropods. Unlike a hermit crab, gastropods continuously grow their shell over their lifetime beginning with a delicate protoconch. They have an organ called the mantle which adds layers of calcium carbonate to the outer edge of the opening of the shell as the gastropod grows. Over its life, the shell elongates spiraling outwards so that the very tip of the spiral is the original shell that the gastropod was born with.

Although the shell is made of inorganic material, the gastropod, which controls the size and weight of its shell over its lifetime, receives proprioceptive feedback from the columellar muscle that anchors the gastropod to its shell. In effect it has shell awareness through its sensory tissues enabling it to map its shell position, monitor the shell’s weight and make adjustments to its balance by changing its posture.

Now back to the hermit crab. I have spent much time observing these intelligent creatures with wonder. They are often around the hotel, and should bad weather be approaching, you can find them (along with crabs) making their way to higher ground or climbing trees and rocks.

Hermit crabs have a soft abdomen which curls and holds on to the central pillar of the shell it inhabits. Without a shell, its survival is at risk for only part of its body possesses a hard exoskeleton. A conscious awareness of its vulnerability when shell-less, can be seen by the way it alters how it explores its environment. When a hermit crab moves to a larger heavier shell it changes its movement and decision making to accommodate its new dimensions. Hermit crabs with well fitting shells exhibit bolder behaviour.

A hermit crab’s sense of self adjusts over its life in a process called embodiment. This is where it integrates a foreign object (new shell) into its own mental body mapping to include its newly acquired dimensions. Its nervous system recalibrates its proprioceptive feedback modifying the hermit crab’s movement and behaviour based on the fit of its extended virtual body.

While hermit crabs may lack a large brain, there is evidence that they possess animal sentience through their capacity to experience feelings of pain, comfort or stress and their ability to exhibit complex decision-making. I have focused on proprioception but it really is worth a look at how they change homes. In brief, a hermit crab when ready to move, loiters around a vacant shell attracting other hermit crabs. As the newcomers arrive, they form a line according to shell size and upgrade together in what has been termed a vacancy chain or conga line.

These quirky and beautiful creatures are such a pleasure to see around the hotel. Some of the older ones are easily recognizable by their battered old shells and elicit such excitement in us when they pass through on their way to wherever. It is comforting to know that they, along with all decapod (having ten legs) crusteaceans such as crabs, lobster and shrimp have been included in the Animal Welfare (Sentience) Act 2022.