Land Hermit Crabs have adapted to live on land and can drown if submerged in water. The abdomen of a hermit crab is very soft and vulnerable; unlike ‘true’ crabs, hermit crabs do not have a hard shell to protect themselves.
To survive, they must tuck their abdomens within the abandoned shell of a marine or land snail (mollusc) to keep their fleshy parts from being eaten/nipped. The rest of the body is protected by an exoskeleton.
Phylum Arthropoda: Animals with specialized body segments, hardened exoskeletons and jointed appendages.
Subphylum Diantennata: Arthropods with a pair of mandibles that flank the mouth and at least one set of antennae.
Class Crustacea: Diantennata with two pairs of antennae and double branched (biramous) appendages.
Order Decapoda: Crustacea with five pairs of legs
Infraorder Anomura: Decapoda, with reduced fifth pair of thoracic legs and the folded up bases above the bases of the fourth pairs of legs.
Family Coenobitidae: Land (Terrestrial) hermit crabs. (Source: Philippe de Vosjoli, 1999)
Land Hermit crabs are a member of anomuran decapod crustaceans, which loosely means ‘false crab’ with ‘ten feet’. Like other Crabs, Prawns and Crayfish, members of Decapoda. Like most species of crab, land hermit crabs have two grasping claws (chelipeds), which they use to eat, climb and grasp.
Coenobita variabilis, the Australian Land (terrestrial) Hermit Crabs which are sold as pets in Australia. The variabilis species come in a range of shapes and sizes, colours, markings and can be found in tropical Australia, including the Northern Territory and Western Australia.
They were until recently colloquially named “Crazy Crabs’, but are now nicknamed “Aussie Hermits” or A.H.’s after confusion with the Caribbean variety land hermit crabs, Coenobita cylpeatus, which are also known by some hermit crabbers online as PP’s, short for ‘Purple Pincers’. Until recently there was much confusion in as to what species the red variety of land hermit crab available in the US was. They have recently been grouped within the C. cylpeatus species and now both types are commonly referred to as C. cylpeatus or CC’s.
Coenobita perlatus. The Red or Strawberry Land Hermit Crab is no longer sold as pets within Australia, but can be found in the wild through the pacific and tropics, including parts of Australia, ( largely on remote islands of the Great Barrier Reef, Queensland, Australia); on Cocos Keeling and Christmas Islands; and other parts of the world. The numbers of Coenobita perlatus are diminishing, due primarily to over-harvesting in the 1970s.
Their close cousins are the Robber or Coconut Crab (Birgus latro) — the largest land crab in the world! They are called Robber Crabs and Coconut Crabs because not only do they like to feast on coconuts in their tropical environment, but they are known to steal items from the front and back yards of homes, even venturing inside to scurry away with a treasure. Coconut Crabs are a type of land hermit crab of the family Coenobitidae which are unique. When they reach maturity, Coconut Crabs no longer need a seashell to protect their vulnerable abdomens, abandoning them to travel in colonies through the rainforests in search of their bounty.
Hermit Crabs do not have a hard shell to protect themselves like true crabs. They have an abdomen, which looks much like the shape of a curled finger, which slips within the safety of a borrowed marine or land snail shell, much like we would slip our feet inside a pair of shoes.
They feel and taste with two sets of antennae: the two long antennae are for feeling around, and the two smaller bent ones used for smelling and hearing.
Land Hermit Crabs have an anus located on the end of their abdomen. They will move their abdomen within their shell to cause the droppings to fall out. Often shaped like small balls or sausage shapes, they consist mostly of sand and other non-digestible foods the hermit crabs eat.
The rest of their anatomy consists of a carapace (or shield) that is made of calcium carbonate, the same as seashells, coral and cuttle- bone. They have a ‘back’ and shoulders (posterior carapace) which is usually much harder than other parts and must be shed along with claws and other sections above the abdomen during a moult as part of their growth cycle.
In the wild, Land Hermit Crabs have adapted to become nocturnal animals, sleeping during the heat of the day evading predators and becoming active at night to wander in search of a tasty treat or a bigger, more comfortable shell for their growing body. They see perfectly well in these nocturnal conditions with two compound eyes perched on top of stalks. In captivity, you will find that hermit crabs have sensitive eyes, and if there is a bright light shining on them, they will hide away from the light by digging down or entering caves
The modified gills are a very special feature of land hermit crabs and their ability to adapt to life on land. Once they come ashore, they ’drop’ their aquatic gills that allowed them to breathe under water, and must now breathe through modified gills that act as lungs. These modified lungs will only work properly if kept moist.
Hermit Crabs, being decapods, have five sets of legs, known as peri- pods. The first pair are known as chelipeds, or grasping claws. Your hermit crab will use these to pull themselves along with the help of the ‘walking’ legs, often lifting the shell off the ground with their strength.
You can tell whether your hermit crab is male or female by the presence of gonopores on the second set. See the section on gender for identification details.
Maxillipeds (Feeding Feet)
A pair of feeding ‘feet’ or ’hands’ (maxillipeds) can be found between the two grasping claws or chelipeds. These small appendages are versatile, enabling hermit crabs to break up pieces of food, pass them to the mouthparts, and also used for grooming.
The two labelled photos are of an Australian Land Hermit Crab, species Coenobita variabilis. Body parts labelled being: Abdomen, Antennae, Anus, Cheliped, Eyes, Modified Gills, Peripods (walking legs), Pleopods (small feet to grip the seashell), Posterior Carapace (inc. branchial chamber), Shield and Uropod.
Land Hermit Crabs are found in the Tropics where it is warm and humid. They are cold-blooded animals and if they are not kept warm they will become inactive to conserve body warmth and eventually die from the stress of the cold.
This is why it is critical to provide them with a warm tropical environment so they can breathe easily and cope with life away from the tropics. If the air within their tank is dry, your hermit crabs will find it very difficult to breathe.
[ Zoea Stages. Scale Measurement is 1.0 mm across. Diagram from BioOne article ]
The life cycle of the land hermit crab is unique. It starts by the release of eggs into an ocean tide pool, where the zoea go through a series of moults and development stages.
A baby hermit crab zoea will be a part of plankton until it grows and starts to resemble hermit crab form. Once they have developed to maturity, hermit crabs leave their watery home, making the long journey to land to find a shell for the protection of the soft abdomen
Once ashore, land hermit crabs go through a metamorphosis, developing modified gills that act as lungs to enable them to breathe air. These lungs must be kept moist, which is one of the reasons why it is important that they choose a shell that fits well and store shell water to keep their gills moist. They live in a variety of environments including trees, mangroves and areas up to 1-2 miles away from the shore.
In the wild some land hermit crabs can spend a long time away from a water source, some only returning to the sea when they are heavy with eggs which they will flick into the intertidal pools to start the cycle over again. Land hermit crabs are instinctive and will access moisture from dewdrops found on leaves of plants. They are able to go without food for a time if necessary and store water in their shells for drinking later.
Hermit crabs are able to regenerate – or regrow – any lost or broken limbs during the moulting process. Hermit Crabs moult because their hard exoskeleton does not grow with their body, and so they must shed it and infuse the new tissues with moisture, then harden these tissues to develop into an exoskeleton with the aid of ‘chitin‘.
During this time, you will need to keep your hermit crab in a comfortably warm and moist environment and offer substrate into which they may burrow within. Some hermit crabs like to dig down deep into the substrate and hide out while their new exoskeleton hardens and they will return to normal activity. For the next 10 or so days heir new skin hardens with the aid of ‘chitin‘ which hermit crabs will obtain by eating their discarded exoskeleton. During this time of natural wonder, you will find your hermit crab is soft, vulnerable, and inactive.
After moulting, your crab will need a bigger shell to protect their newly moulted body. Your hermit crab may be a little crabby after a moult and you should offer a variety of shells for them to choose from. Hermit crabs love to size up new shells and will often change shells for hours on end until they find their favourite.
How long your hermit crab will survive in captivity will depend on factors such as environment, diet, exercise, freedom from disease and general health and wellbeing; the very same factors as in the wild. No two hermit crabs are the same and it is often puzzling that some hermit crabs will live for 25 years, while others will perish even under the best of conditions.
n average lifespan in an incorrect environment for land hermit crabs as pets is around a year, usually when they try to moult. If the level of care is high, there is every chance that your hermit crabs could live to the ripe old age of 25 or 30. Carol of Crabworks had two hermit crabs;
Crab Kate lived to thirty-five years in captivity before passing. Jonathon Livingstone Crab is still alive at over 40 years of age. Carol has raised them from small land hermit crabs to ones close to the size of tennis balls.
You can visit her gallery of photos (listed in recommended websites) to observe the changes in size, colour and appearance over the years under Carol’s expert care.
Glossary of Terms related to Hermit Crabs
Abdomen: Region of the body furthest from the mouth. In insects, the third body region behind the head and thorax.
Antennae: sense organs also known as ‘feelers’ help the hermit crab smell and taste. A hermit crab has two pairs of anteannae at the front of their head, with two being long and two being short. The long pair are called antennas and the short pair antennules. Antennas are used to touch and sense other hermit crabs and objects.The antennules are what a hermit crab uses to smell and taste.
Antennule: a small antenna, esp. one of the foremost pair of a crustacean. 1
Anus: Located at the end of the hermit crab’s abdomen. (Fox, S. 2000 p.13)
Atoll: (Pronounced a-tahl). Type of island that is formed when the top of an underwater volcano that was once above the water sinks below the surface, leaving only the coral reef and sandbars in a ring around a lagoon.
Autotomy: also called Self-amputation, the ability of certain animals to release part of the body that has been grasped by an external agent.EB
Carcinology n. study of crustaceans. carcinomorphic, a. like a crab or crustacean.
C.C. : 1. CrazyCrab: Now known as Aussie Hermits, a land hermit crab of the species C. variabilis; 2. Coenobita clypeatus
Carapace: “The portion of cepalthorax that covers the top of the crab forms a hard protective shield called the carapace” (Fox, S. 2000 p.13)
Carnivorous: an animal that eats meat
Cephalothorax : The hermit crab’s head, which contains its mouth, eyes and antennae, is fused to its thorax and is known as the cepalthorax. The crab’s five pair of legs are attached to the thorax. The portion of the cepalthorax that covers the top of the crab forms a hard protective shield called the carapace
Chela: (Pronounced kee-la) a pincer
Cheliped: (Pronounced kee-li-ped) chelipeds (chela=”claw” and ped=”foot”).. Also called grasping claws because of the non-aggressive ways they are used, the chelipeds are what a hermit crab uses to grip while climbing and protect during a crab fight. When eating, you will notice a hermit crab hold the food with one cheliped, and break the food off with the other, passing it to the maxillipeds. The left claw is usually (depending on species) used for climbing or defence. When a hermit crab withdraws within its shell it will use its larger claw to block the entrance to the shell. The right claw is usually used for eating and climbing. Cheliped – (in decapod crustaceans) either of the pair of appendages bearing a chela. 2.
Chitin : (Pronounced KY-tin) In arthropods the chitinous shell, or exoskeleton, covers the surface of the body, does not grow, and is periodically cast off (moulted). After the old shell is shed, a new, larger shell is secreted by the epidermis, providing room for future growth. The chitin is rigid except between somebody segments and joints where it is thin and allows movement of adjacent parts. 3
Clypeatus: (Pronounced ) shield-shaped
Coenobita: (pronounced ‘seen-oh-bit-a’) Family of terrestrial (land-based) hermit crabs.
Compound Eye: Photoreceptor of Arthropods that consists of several ommatidia. It has no lid but is covered with an exoskeleton.
Compressus: From the word compress [latin]. In Coenobita compressus it may have been used to describe the ‘compressed’ eye shape of a C. compressus land hermit crab.
Crustacean: a class of mainly aquatic animals including lobsters, crabs, shrimps, prawns etc 4
Cuticle — In animals, a multilayered, extracellular, external body covering, usually composed of fibrous molecules such as chitin or collagen, and sometimes strengthened by the deposition of minerals such as calcium carbonate.
Detritus: (Pronounced dee-triy-tis). Decomposing organic material
Ecdysis: (Pronounced ek-diy-sis). Stage in athropod moulting in which the old exoskeleton is shed and the new enlarged with water and/or air.
Ecdysone: (pronounced ek-diy-son). In insects, crustaceans ando ther arthropods, the hormone that directly affects the epidermal cells during moulting.
Ecuadorian hermit crab aka E’s : hermit crab that comes from Ecuador of the species Coenobita compressus. Visit the crab species site
Epicuticle: The waxy outer layer of the Arthropod exoskeleton
Exoskeleton: “The crab’s exoskeleton is made from layers of protein and chitin. The exoskeleton, or cuticle, is hardened by calcium carbonate… The exoskeleton protects the animal and provides points of attachment for the muscles to move the appendages. It helps impede water loss, although a crab still slowly loses water across its exoskeleton.” (Fox, S. 2000 p.11)
Faeces: Digestive waste
Feeding Appendages: see Maxillipeds
Fifth legs: small legs that are kept hidden within the shell. Used to maneuver the shell and hold itself within the shell.
Gastroliths: Deposit of calcium salts made in the stomach of many crustaceans during the period between moults. It may be used to store calcium needed in the new exoskeleton.
Gills: 1. A hermit crab’s gills are enclose din the branchial chamber, which functions as a lung. The branchial chamber is on the sides of the thorax, above the crab’s legs. 2. gill — In aquatic animals, highly vascularized tissues with large surface area; these are extended out of the body and into the surrounding water for gas exchange.
Gonoduct: (Gah-no-dukt). Any duct that generally transfers eggs or sperm.
1. an opening through which eggs or sperm are released, esp. in invertebrates. 5
2. any opening between the reproductive system and the outside.
Hairs: “The long hairs that you see between the joint of your crab’s legs, on the maxillipeds, along the inside of some appendages, and near its mouth are called setae. Unlike the hair that grows on yor head, setae do not grow from hair follicles. They are actually extensions of the crab’s cuticle. When a crab molts its exoskeleton, these “hairs” are also shed as projections of the exoskeleton. (Fox, S. 2000 p.12)
Invertebrate: creatures without a backbone 6
KritterKeeper (KK) : Name of the plastic tanks manufactured by Lees that are the most well-known type available in the US. Many people adopted calling all plastic tanks KK
Larvae: stage of development
Larval stages of Development: stages hermit crab larvae go through before progressing to the next stage of development
Maxillipeds : (Pronounced maks-il-li-ped) also known as feeding appendages, maxillipeds are very small appendages near your crab’s mouth. They are like tiny little hands that take food from the chelipeds and feed the foodstuffs within the very small mouth. Maxillipeds are also used to groom itself and you will often see them when you handfeed your hermit crab.
Megalops: (Pronounced meg-a-lahps) Larval stage following the zoea larva. Post-larva.
Metamorphoses, Metamorphosed :
1. a process in which the exoskeleton, or outer skin, is shed and a new exo is grown. It is also a time during which lost limbs are regenerated/regrown and your hermit crab will grow slightly as the new tissues swell with fluids and then harden with the aid of chitin.
2. The hormonally-controlled process of shedding one cuticle (or exoskeleton) in order to allow growth of the organism and the subsequent replacement of the cuticle.
Nocturnal: Inactive during day, active at night. Creatures such as owls are nocturnal, where they sleep during the day and hunt for food at night. In the heat of the day, hermit crabs hide beneath foliage/leaf litter or in trees and sleep, then after sundown you can see hermit crabs on the beaches in search of fish washed up on the beach, and other carrion.
Periopod: describes the four pairs of legs which are appendages of the thorax. Includes the second and third pairs which are used for walking. The fourth and fifth which are small and usually hidden within the shell. The fourth and fifth legs are used to maneuver the shell and hold itself within the shell.
Phylogeny: (Pronounced fi-lah-je-nee). The evolutionary relationships between groups of organisms.
Pleopod: leg of a crab 7. “The pleopods are small appendages located on the left side of the crab’s abdomen. A female crab attaches her eggs to the fine setae on her pleopods using a gluelike substance. Male land hermit crabs also have pleopods, but they are much smaller and not nearly as hairy.
Proecydysis (Pronounced pro-ek-diy-sis). The first stage of Arthropod molting in which the body prepares to shed the exoskeleton. In Crustaceans, the blood absorbs calcium from the exoskeleton and makes gastroliths.
Protocuticle: The inner layer of Arthropod exoskeletons that lies just under the epicuticle
Purple Pincer/Claw Hermit Crab : hermit crab that is distinguished by a purple claw and round eyes, as opposed to compressed eyes of Ecuadorian (E) crabs. Visit the crab species
Regeneration. Ability to reproduce a severed body part.
Sand Dollar: The common name for certain irregular echinoids (Echinodermata)
Setae: The long hairs that grow between the joints of your crab’s legs, on the maxillipeds, along the inside of some appendages, and near its mouth are called setae. Unlike the hair that grows on your head, setae do not grow from hair follicles. They are actually extensions of the crab’s cuticle. When a crab molts its exoskeleton, these “hairs” are also shed as projections of the exoskeleton.” (Fox, S. 2000 p.12)
Telson (Pronounced tel-son) A medial section at the very posterior of most Arthropods: it bears the anus.
Uropods: “At the tip of a crab’s abdomen are small appendages called uropods. Although you will never see them, they perform an important function. The uropods hook onto the spiral of the shell and help the crab to grip its shell.”
Variabilis – Changeable [latin]
Vascular — Refers to a network of tubes which distribute nutrients and remove wates from the tissues of the body. Large multicellular animals must rely on a vascular system to keep their cells nourished and alive.
Zoea/Zoeae: (Pronounced zo-ee-a).
1. Any of the free-swimming larva of certain crustaceans, as the crab, having rudimentary legs and a spiny carapace. 8
2. Larval stage that follows the ‘protozoea’.
Fox, Sue (2000) Hermit Crabs : Complete Pet Owner’s Guide. Barrons Books : N.Y.
Introduction to the Arthropoda. . . the REAL rulers of the Earth. . .
Renae Brodie and Alan W. Harvey “LARVAL DEVELOPMENT OF THE LAND HERMIT CRAB COENOBITA COMPRESSUS H. MILNE EDWARDS REARED IN THE LABORATORY,” Journal of Crustacean Biology 21(3), 715-732, (1 August 2001).
The Crab Street Journal Biology Articles