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Where Do Hermit Crabs Get Their Shells?

Hermit crabs aren’t born with shells, so they must be acquired from other animals. Size, durability, scent, and mobility are among the many important criteria that hermit crabs look for in a shell.

Wild hermit crabs scavenge their shells. Usually, these shells will be vacated by another crab or sea snail that died or upgraded to a bigger shell. They’ll then change their shells many times during their lifetime.

While young, hermit crabs regularly outgrow their shells. As adults, hermit crabs look to upgrade or exchange shells for a new shell that’s more suitable.

Providing different shell options keeps pet hermit crabs happy.

Are Hermit Crabs Born with Shells?

Hermit crabs aren’t true crabs in that they’re not born with shells. Instead, they must source shells to protect their exoskeleton. A hermit crab without a shell is easy for predators to pick off.

All hermit crabs start life as zoeae. Females carry eggs, which enter the ocean when ready to hatch. These eggs explode upon contact with water, and the zoeae are born. These are tiny larvae that float with plankton.

If a zoea survives for around 60 days, it will evolve into a megalopa. This is a tiny aquatic specimen, and hermit crabs find their first shell at this stage. The megalopa life stage of a hermit crab lasts around 30 days.

If hermit crabs last this long, they will bury themselves in sand and molt. Upon emerging, a molted megalopa is a juvenile hermit crab that needs a constant cycle of shells to keep up with growth to survive into adulthood.

How Do Hermit Crabs Get Their First Shell?

The Journal of Experimental Marine Biology and Ecology explains that a megalopa claims its first shell in the ocean. As the animal is so minuscule at this stage, this will usually be a shell vacated by a sea snail.

A megalopa uses this shell to protect itself once it reaches land. The megalopa will grow lungs and enhanced gills to adapt to terrestrial life. The megalopa will remain tiny – around the size of a fingernail, and it may settle for a bottle top if it needs a new shell.

After evolving into a juvenile hermit crab, the shell search begins in earnest. Like all young animals, juvenile hermit crabs are vulnerable. As their mothers don’t raise them, hermit crabs must learn how to survive immediately, which involves finding a sturdy vacant shell.

Juvenile hermit crabs constantly outgrow their shells. Revista Chilena de Historia Natural explains that some hermit crabs deliberately delay growth and development. The smaller the hermit crab is, the more shells it will have to choose from.

Medium-sized shells are the hardest to find, while small shells are plentiful, as they can be claimed from gastropods. Large shells are abundant but more coveted by adult hermit crabs, and juvenile hermit crabs will rarely best an elder in conflict.

are hermit crabs born with shells?

Where Do Hermit Crabs Find Their Shells?

Hermit crabs in the wild find new shells while scavenging. Hunting new shells is a major part of a hermit crab’s routine. Many choose to locate themselves in a territory with a plentiful supply of new shells.

Most hermit crabs rely on seawater to locate shells. Animal Behavior explains that the presence of water vapor enhances the senses of hermit crabs, which makes shells easier to locate. Without access to water, hermit crabs grow disoriented and confused.

Changing shells is a double-edged sword for hermit crabs, as they must leave their mobile shelter to move into a new shell, making them vulnerable to predators. A hermit crab will only consider trading shells if the new home appears appealing.

Hermit crabs captured by seafront shop owners for sale will already have shells. Shop owners paint these shells in a range of colors, which is a sales technique designed to appeal to shoppers.

Hermit crabs are indifferent to the aesthetics of shells. Painting shells can be dangerous, as hermit crabs can find themselves glued inside a shell by wet paint or breathe in toxic paint fumes.

How Do Hermit Crabs Get New Shells?

Hermit crabs leave their existing shell reluctantly when it’s safe. They will only leave their shells when no predators are nearby, and the sun isn’t high.

The hermit crab will “try on” a new shell. If it feels comfortable, it will stay put. If not, it will return to its previous shell before another hermit crab can claim it. There are three ways that a hermit crab will source a new shell.

Scavenging for Empty Shells

Hermit crabs trawl the beachfront for food. In doing so, they will also seek out spare shells. If a hermit crab finds a shell more suitable for its needs than the vessel it occupies, it will consider changing.

This could be an empty seashell, the remanent of a dead gastropod, or, as we’ll discuss in a moment, the shell of a dead conspecific. The hermit crab may not like the new shell and return to its existing one. Some hermit crabs will remain in a new mobile home, though.

Scavenging hermit crabs can grow confused. Litter is a significant cause of mortality in wild hermit crabs. These crustaceans climb inside empty plastic bottles, for example, and can’t get out again.

Dead Hermit Crabs

When a hermit crab dies, it releases a distinctive pheromone. Ecology and Evolution explain that other hermit crabs will pick up this scent, and surviving crabs will come to investigate.

This isn’t hermit crabs being ghoulish, though this species resorts to cannibalism to survive if necessary. Instead, the release of the pheromone announces the availability of a shell.

As hermit crabs live in colonies and are social, they are concerned with the continuation of their species. Ergo, releasing this ‘death scent‘ is an attempt to allow life to go on for others. The dying hermit crab ensures that a perfectly good shell doesn’t go to waste.

Fighting Other Hermit Crabs

Captive hermit crabs enjoy living in groups. Despite this, hermit crabs will come into conflict on occasion. This will usually take the form of shell rapping, which involves a dominant hermit crab knocking on the shell of another.

Hermit crabs engage in shell rapping when one hermit crab covets the shell of another. This may happen when it’s outgrowing its current shell, so it’ll challenge the second hermit crab to a conflict. If the aggressor wins, the hermit crabs switch shells.

As explained by Behavior, not all shell rapping among hermit crabs results in a winner and a loser. It is possible that both hermit crabs will be happy with the outcome. If the evicted hermit crab is contented with the trade, all parties are pleased with the outcome.

How Often Do Hermit Crabs Change Shell?

In the first 1-2 years of life, hermit crabs change their shell constantly. Hermit crabs grow quickly, and males experience particular growth spurts immediately preceding molting.

Females change shells less frequently because they grow slower. This is a natural evolution.

Pregnant hermit crabs carry eggs in three appendages on the abdomen. The female’s body remains smaller, so it has a greater choice of shells large enough to offer protection. For this reason, most females reproduce in their first year of life.

Whatever the sex of a hermit crab, it will change shells periodically. This may be an act of necessity. Hermit crabs can be trapped in a shell if they outgrow it. Equally, the shell may be damaged by conflict or wear and tear. Equally, the hermit crab may just want a change.

Post-Molting

When a hermit crab molts, it grows a new exoskeleton. This usually sees the hermit crab increasing in size and mass – sometimes drastically so. This means the hermit crab will need a new shell.

Hermit crabs will often take their shells with them when burrowing to molt. This is because hermit crabs store water supplies in their shells, keeping them alive during the underground molting process. A molt may take several weeks or even months.

Molting hermit crabs should be separated from tankmates. Arrange this before the molt begins, as a molting hermit crab should never be disturbed. Signs that a hermit crab is preparing to molt include:

  • Growing sluggish
  • Eating and drinking more than usual
  • Digging a lot
  • Exoskeleton fading to a dull gray
  • Glazed, milky look in the eyes

Immediately post-molting, hermit crabs lack a shell. The previous shell may be recycled but likely cracked and splintered during molting. With no shell, a hermit crab is vulnerable. Keep it alone with a selection of new shells. Once a shell has been chosen, return the hermit crab to its friends.

After Conflict

As discussed above, inter-hermit crab conflict can result in shell trading. In theory, this isn’t a problem, as long as all hermit crabs have shells.

Monitor this practice, as all hermit crabs have a unique personality, and some may be more docile and submissive than others. That makes it possible for hermit crabs to be bullied.

If you notice one particular hermit crab is constantly being ousted from its shell, consider rehoming it. If the same thing happens again, keep the hermit crab alone. While most hermit crabs prefer company, it can be dangerous and stressful to be regularly evicted.

General Changing

Sometimes, hermit crabs just want a change of scene, so they may change their shell for increased mobility, greater protection, or boredom.

Factor this into any selection of shells for your hermit crabs. Offer an array of different shapes and sizes. As mentioned, hermit crabs don’t care about the colors or designs of shells. Accessibility of shells is pivotal, though.

How Do Hermit Crabs Choose Their Shells?

Many factors influence shell selection in hermit crabs. Choosing a shell for a hermit crab is akin to picking a home for humans. Just as you would prefer not to take the first house or apartment you see, hermit crabs take their time finding the perfect shell.

When a shell becomes available, hermit crabs often line up to review it. They will take it in turns to try the shell on for size. There is a pecking order in any hermit crab colony, whether wild or domesticated. If a dominant hermit crab likes a new shell, it will be claimed.

This creates a domino effect among the remaining hermit crabs. To return to our house purchasing metaphor, this is the chain of properties. The shell vacated by the dominant hermit crab is now available, and the process will begin anew until every crab is satisfied.

To return to our initial question, though – what do hermit crabs look for in a shell? Any permanent mobile home for hermit crabs must meet four key criteria.

Smell

The scent of a shell is pivotal to hermit crabs, which is the most dominant sense in a hermit crab’s arsenal. If the shell smells entirely neutral, it will likely be rejected.

It’ll be more appealing if the shell carries the scent of another crab or gastropod. Equally, the scent of saltwater may be enough to tempt the hermit crab.

how do hermit crabs choose their shells?

Size

The size of a hermit crab’s shell is arguably the primary concern, but bigger isn’t always better. As discussed, a large shell may attract unwanted attention from rivals. Equally, a large, heavy shell may be cumbersome.

The size of the hole that a hermit crab enters is all-important, though. Hermit crabs seek a shell that makes them feel safe but not snug. If the hole a hermit crab enters and exits from is too small, the hermit crab can get stuck, creating feelings of panic.

Durability

A hermit crab’s shell is a source of protection from predators and the elements. As a result, it needs to be sturdy and tough enough to stave off the sun’s rays.

Hermit crabs may rap upon a shell to check how tough it is. Hermit crabs are aware of the strength of a shell. If a shell grows cracked and damaged, hermit crabs feel exposed and become increasingly belligerent.

Mobility

Hermit crabs seek shells that afford sufficient mobility. Hermit crabs need to walk comfortably with a shell upon their back. Failure to access food due to the weight of the shell will become distressing.

Hermit crabs can also become trapped if their shell is immobilizing. Hermit crabs will flee and hide if they feel threatened. If the shell is too cumbersome, it may get stuck between aquarium walls and obstacles.

Should I Change My Hermit Crab’s Shells?

You can purchase a range of shells online or from an exotic pet specialist. Any merchant that handles hermit crabs regularly will have a selection of suitable shells. You can usually browse by size, shape, and style.

Never force hermit crabs to change shells against their will. Hermit crabs ferociously guard their shells. If you try to pull a hermit crab out of its shell, it’ll resist emerging. Hermit crabs would rather be torn limb from limb than relinquish a shell by force.

You can certainly offer your hermit crabs a variety of shells. Leave these in an aquarium. Just dot them around the substrate. The hermit crabs will investigate at their leisure. If interested, the hermit crabs will try on these shells. This will typically happen after dark.

Eventually, hermit crabs switch shells, whether through choice or necessity.

Encouraging Hermit Crabs to Change Shells

If you are concerned that the shells of your hermit crabs are too small or otherwise unsuitable, try to encourage change. Offer a wide selection of shells. Hermit crabs enjoy having a variety.

Moisten the inside of the shells with boiled seawater to make them more appealing to hermit crabs. Marine and Freshwater Behavior and Physiology confirm that hermit crabs are attracted to boiled shells. Never use tap water as it contains chlorine and copper, as they’re fatal for hermit crabs.

If your hermit crabs haven’t changed shells overnight, do not take the alternatives away. The hermit crabs may be happy with their current shells, and there’s no way of knowing when this will change. Existing shells may crack, be outgrown, or cause conflict.

With this in mind, remove the shells and remoisten them roughly once a week. Keep repeating this process. Eventually, your hermit crabs will grow curious enough to investigate.

Hermit crabs like to find shells by themselves and choose when to switch home. In the wild, this will be a natural process. In captivity, you can offer an array of shells to choose from. In doing so, you’ll keep your hermit crabs happy and engaged.