Hermit crabs need shells to survive in the wild and captivity. No hermit crab will retain the same shell for life, as they must upgrade to larger shells as their size increases.
When a hermit crab leaves its shell, this is called shell evacuation.
Most hermit crabs won’t evacuate a shell that meets their needs. If the shell is large enough to accommodate it and provides protection from external threats, a hermit crab will guard it jealously.
If the hermit crab molts, it’ll increase in size and mass. It’ll evacuate its shell so it doesn’t become trapped once the molt is complete. Once the process is complete, the hermit crab will seek a new shell.
A hermit crab will seek a safer, more robust alternative if a shell is cracked or damaged. Also, hermit crabs evacuate shells that are too cumbersome to maneuver or when a rival challenges them over the shell.
Hermit crab evacuation isn’t always an emergency. The hermit crab will find a superior replacement if it has access to an alternative shell that meets its needs.
If a hermit crab remains out of its shell, this could be due to an environmental factor that must be resolved. For example, the temperature in the tank is too high, or there’s no water.
How Long Can a Hermit Crab Survive Without a Shell?
Shells are a necessity for hermit crabs. The exoskeleton isn’t sturdy enough to resist impact injuries if it falls from the roof of its tank and can’t shield it from the sun’s harmful UV rays.
A hermit crab must immediately find a replacement if it evacuates its shell. Ensure spare shells are available for pet hermit crabs because an evacuation must only be short-term.
Why Do Hermit Crabs Leave Their Shells?
Hermit crabs don’t decide to leave their shells unless they know something is wrong. If a hermit crab vacates a shell, you must learn why it suddenly happened.
Inappropriate Environment
Hermit crabs require a tank that mirrors their natural habitat to thrive. This includes:
- An ambient temperature of around 80°F.
- Humidity levels of 80% to avoid suffocation.
- No less than 6 inches of substrate for burrowing.
- Water to bathe in and drink. For example, submerging in water to kill mites.
If its needs are unmet, hermit crabs grow uncomfortable. If a hermit crab feels too hot, unable to breathe, or otherwise distressed, it may evacuate the shell, hoping to improve its conditions.
Discomfort in The Shell
If the conditions in a tank meet the needs of a hermit crab and other residents feel comfortable in the environment, check the shell’s interior post-evacuation.
Sand may have got into the shell, rubbing against the vulnerable skin and causing irritation.
Check for signs of parasites. The Journal of Experimental Marine Biology and Ecology stated that mites and other pests can enter a shell, making life difficult and uncomfortable.
Molting
When a hermit crab molts its exoskeleton, it’ll usually due to an increase in size. This increase in mass is most notable for the first 18 months of life when a hermit crab molts most frequently.
Most evacuate during the process because a shell is usually too small for a hermit crab after molting. The hermit crab won’t evacuate entirely before commencing a molt.
Bathing
You may notice a hermit crab out of its shell in its water dish, especially in saline water. This allows the hermit crab to douse its gills, keeping them damp and making breathing easier.
Many hermit crabs initially enter the water in their shells, filling them with water. This is especially likely pre-molt because it’ll retain sufficient moisture while hiding under the substrate.
If the hermit crab leaves the shell for water, this isn’t of immediate concern.
Monitor the hermit crab and remove it from submersion if more than 15-20 minutes have passed. Land-based hermit crabs can’t breathe underwater indefinitely, so they’ll drown.
Shell No Longer Fit for Purpose
If a shell is cracked or broken, it could be uncomfortable or no longer provide adequate protection.
The hermit crab will almost immediately seek to trade the shell for a replacement. The longer it remains in a substandard shell, the likelier it is to succumb to harm.
A hermit crab with a particularly heavy shell may be unable to maneuver. Hermit crabs have impressive proportional strength but can’t move freely in a too-large or cumbersome shell.
Competition from Rival Hermit Crabs
Hermit crabs usually live side-by-side with little conflict, but disputes sometimes arise. Hermit crabs may fight over territory, mating rights, and the best shells because they’re hierarchical animals.
The journal Proceedings of the Royal Society discusses how hermit crabs instigate feeler fights over particularly desirable shells, coveting shelters that belong to rivals.
If the incumbent hermit crab has no interest in fighting, it’ll hide inside until the aggressor leaves.
How Does a Hermit Crab Switch Shells?
When a hermit crab is ready to change shells, it becomes a group activity.
One evacuation starts a chain that involves the entire colony, the members of which line up based on size. The first hermit crab crawls out of its shell and into a new, more suitable replacement.
Once the hermit crab that evacuated has a new shell, its old one is available for other hermit crabs. The largest, most dominant hermit crab will evacuate its existing shell and try on the now-vacant replacement.
If this hermit crab likes the shell, the process continues. The next one in line will try on the most recently evacuated shell, so the chain continues.
Exchanging shells following an evacuation is usually a peaceful and mutually beneficial experience.
Why Did My Hermit Crab Come Out of its Shell and Die?
All living creatures die eventually, and hermit crabs are no exception. Nobody can be certain if hermit crabs perceive their mortality, but it’s common for them to evacuate a shell before death.
When hermit crabs die, they release an unmistakable odor akin to rotten fish. Ecology and Evolution explain how this aroma attracts other hermit crabs.
Part of this is hermit crabs’ omnivorous, scavenging nature because they consume dead members of their species. Equally, a deceased hermit crab means a quality shell is now vacant.
As with many small animals, the species’ survival is pivotal to hermit crabs. By vacating a shell before death, a hermit crab enhances the likelihood of survival for another colony member.
Hermit crab evacuation should be considered on par with moving house. Leaving a shell isn’t done without due thought because they’re shy and cautious animals, but it’s sometimes essential.
Ensure other quality, suitably-sized shells are available in the tank if a hermit crab decides or has no choice but to vacate its shell. This will prevent conflict and avoid stressful situations.
