Moulting... the Crisis
So what is moulting?
by Vanessa Pike-Russell
Arthropods (e.g., insects and crustaceans) must molt their exoskeletons periodically in order to grow; in this process the inner layers of the old cuticle are digested by a molting fluid secreted by the epidermal cells, the animal emerges from the old covering, and the new cuticle hardens. Encyclopedia.com
The growth cycle of a land hermit crab is based on a process known as molting (or moulting), often triggered by the amount a hermit crab eats and drinks.
Hermit crabs have rigid 
exoskeleton which cover the eyes, claws (chelipeds), legs (peripods) and parts of the shield and posterior carapace. These areas do not grow as the crab grows, and need to be shed.
A hermit crab will shed their exoskeleton when it becomes too snug about their growing body. Hermit crabs cannot go shopping for new skin, they instead shed their exoskeleton and build up the tender tissues with fluids and evelop a hardened exoskeleton. To be able to do this, your hermit crab will need a lot of moisture. You might find your crab near the water dish a lot prior to a moult. If you were to watch your crab moult, you would see your crab stretch and twist until the exoskeleton splits, then slips out of it like a suit. Some crabs cannot do this in one piece, so you may see legs and claws strewn about.
[Molted Exoskeleton of Crab Kate, one of two
28 yr. old land hermit crabs owned by Carol of CrabWorks.]
[ Images used with permission.Copyright ©1999-2005 Carol of CrabWorks ]
Once your crab has slipped free of that constricting exoskeleton they will either retreat into the safety of a large shell or bury down into the sand or other fine substrate to hide away for a time. There are some cases where a hermit crab would do neither of these and choose to moult above the substrate and is visible throughout the moulting period. It all depends on the crab and how safe he feels within his crabarium and the type of substrate offered.
Arthropods moult periodically in order to grow and mature. Triggered by hormones released when its growth reaches the physical limits of itsexoskeleton, the moulting begins (apolysis) when the cuticle separates from the epidermis due to the secretion of a moulting fluid into the exuvial (cast-off skin or cuticle) space. The endocuticle (chitinous inner layer of the cuticle) is then reabsorbed and a new epicuticle (outer, shiny or waxy layer) secreted. Ecdysis is the act of shedding whatever remains of the old cuticle.
Step 1: Apolysis -- separation of old exoskeleton from epidermis
Step 2: Secretion of inactive molting fluid by epidermis
Step 3: Production of cuticulin layer for new exoskeleton
Step 4: Activation of molting fluid
Step 5: Digestion and absorption of old endocuticle
Step 6: Epidermis secretes new procuticle
Step 7: Ecdysis -- shedding the old exo- and epicuticle
Step 8: Expansion of new integument(covering or investing layer)
Step 9: Tanning -- sclerotization(The hardening and darkening processes in the cuticle (involves the epicuticle and exocuticle with a substance called sclerotin) of new exocuticle. Now the chitin and protein are laid down and the exoskeleton will become hardened and shiny after a few weeks like Wumba in the post-moult photos.
[Images of Wumba by Vanessa, January 2002]
In the photos supplied by MrsPoppyPuff below, you can see how her crab pulled out of its exoskeleton.
One this painful part of the process is over, your crab will now need to recover in the least stressful of environments. The temperature and humidity should be kept in the ideal range of 70-80oF (21-27oC).
"Typically premoult animals enter their burrows with their abdomens markedly swollen by food reserves... After moulting the animal eats its exuviae,which contribute organic materials and calcium salts needed for the new skeleton... Very little information is available in regard to moulting of Coenobita. Coenobita clypeatus is reported to hide during the process most of which occurs in the shell (de Wilde, 1973). There is a noticeable reduction in activity for several days prior to the moult and after ecdysis the exuviae are positioned just in front of the mouth of the shell (A.W. Harvey, pers. comm.). During calcification the new soft skeleton of the chelae and other walking legs is moulded to fit the shape of the shell. If the animal increases markedly in size it may no longer fit neatly within the old shell and a rapid trade up in shell size may be necessary to avoid water loss and predators. There is no information available on calcium balance or storage through the moult or on growth increments of Coenobita. Coenobita clypeatus grows up to 500 g if large-enough shells are available" (Greenaway, P. 2003 p. 21)
Land Hermit Crabs that are eating foods high in calcium, fiber, chitin and foods high in nutrients their bodies need will often have a much higher moulting rate; which slows with age or lack of larger seashells. If a crab is in a seashell, which is snug with no alternatives, they will not moult as readily as one with a vast selection.
Exercise is known to increase hunger, and thus will affect the rate of moulting. In the wild, land hermit crabs have been known to walk many miles a night, and graze on foods along the way. It would depend on location as to the amount of exercise and grazing a hermit crab will do, but we have to be aware that a hermit crab stuck in a tank will not be as strong and healthy as one which is allowed out of the tank.
A hermit crab can be safely exercised out of the tank within the safety of a plastic crab ball, and allowed to roam and climb more than the height and width of their crabitat. I have watched my larger hermit crabs navigate a crab ball up and down stairs, around obstacles and an increase in skill after problem solving. After such exertion, their appetites increased and the food dish emptied in no time!
Scientist Mike Oesterling of the Virginia Institute of Marine Science has noted this in Blue Crabs.
"In the summer months, food availability has a major affect on shedding activity. If a crab does not satisfy the physiological need to shed (increased muscle tissue, body cavity 'cramping', etc.), it will not enter the molting cycle. In other words, if it doesn't get adequate nutrition it's not going to grow." (Oesterling, M. 2003)
Hermit Crabs are social animals, and as such, there is usually a ‘pecking order’ among groups or colonies. As with many animals and organisms, when there is a scarcity of resources you will see a ‘pecking order’ among hermit crabs. The resources most important to hermit crabs being protein and calcium-rich foods and varied diet; hiding spots; space to dig down to moult; different sizes of seashells; water; and salt water (brackish – 50% salinity).
If a crab is 'top crab' than it would get the most food, like with puppies and seagulls. We see this on a small scale within the crabarium, where hermit crabs vie for position in the food bowl or a favourite hiding spot. I have often watched my jumbo hermit crabs fighting for access to the salt-water bowl or Treat dish. It is not unusual for them to fill the bowl completely and keep other hermit crabs away, defending their right to eat first.
Hermit Crabs grow through moulting. If you notice a hermit crab pre and post moult you will see very little difference, but over ten or twenty years it is quite significant. Another way to tell age is to look at the thickness of antennae and the little 'teeth' on the cheliped/grasping claw.Moulting allows them to grow and regenerate any missing limbs You might have experienced the wonder and surprise at seeing a snake shed his skin. The shed skin looks like a duplicate of the snake, but it is only the cast off skin that didn't grow with the snake. When a hermit crab grows its exoskeleton (skin) doesn't. Imagine a pair of tight-fitting shoes. When your feet grow, your shoes do not. You need to go and get some new shoes which will fit.
To be able to moult, your hermit crab will need a lot of moisture. You might find your crab near the water dish a lot prior to a moult. If you were to watch your crab moult, you would see your crab stretch and twist until the exo splits, then slips out of it like a suit. Some crabs cannot do this in one piece, so you may see legs and claws strewn about. It is important that you do not discard the exoskeleton or body parts, or disturb your land hermit crab while it recovers from the moult. The exoskeleton contains the nutrients your crab needs for the Tanning stage of moulting.
"Land Crabs store large quantities of lipids in the hepatopancreas, perhaps representing an adaptation to the variability of terrestrial environments. Unfortunately, few comparative data are available. Charles Darwin (cited in Reyne, 1939) remarked on the fact that over a liter of oil could be rendered from a large B. latro. The hepatopancreas of this animal contains up to 83% lipid (Lawrence, 1970; Storch, Janssen, and Cases, 1982), becoming particularly fat prior to molt (Wiens, 1962). Land crabs may rely heavily on "lipid economy". Lipid biosynthesis increasesmarkedly prior to ecdysis (O'Conor and Gilbert, 1968) concurrent with the degradation of muscle (particularly the chelae) that permits extracting the limbs through narrow joints in the old exoskeleton (Skinner, 1966b). Subsequent regeneration of muscle, and growth of new muscle tissue, will require nitrogen sources if based on stored lipids" (Wolcott, T. G. 1988. p 90)
Observed Premolt Symptoms
by Marie Davis
At times, crabbers become concerned due to certain actions their hermit crabs are beginning to display. Often, they are concerned that the hermit crab is ill, or has another form of complication happening that needs attention. Where, as on occasions, the symptoms they are observing may be due to a stressful situation, whether it be from their past or current living conditions, there are many times that the hermit crab is displaying premolt symptoms. If one knows that he/she has provided the hermit crab with the essentials it needs to thrive (proper humidity level, proper temperature, proper diet, bacteria/mold and a pest-free environment, etc.), what you are beginning to observe may very well be premolt symptoms that the hermit crab is displaying.
With the numerous molts we have had, I would like to share some of the premolt symptoms I have observed with our hermit crabs and hope it can be of some help to ease other crabbers’ concerns.
Please note that not all hermit crabs will display premolt symptoms prior to molting. Some will do a surprise molt displaying no symptoms, but here are some we have noted with our hermit crabs:
1. Gorging food for almost 2 weeks prior to molting.
2. A few days--up to and including almost 2 weeks prior to molting--consuming no food at all.
3. Very restless behavior during the daylight and evening hours, including attempting to climb the glass walls inside of the crabitat as though they are looking for a way out.
4. Dragging their large cheliped almost under them as though it is too heavy to hold up, or in front of them as opposed to being slightly in front of them when they are scooting.
5. The V shaped eye stalks _/ as opposed to the typical parallel eye stalk shape. |_| The pupil of the eye stalk looks as though they are looking outward <_> as opposed to straight ahead.
6. Eye stalks in a downward position as opposed to a standing up type position. When the eye stalks are in this position, this means that the hermit crab is very close to molting, or has already begun the actual molting process to remove its exoskeleton. By no means at this time should the hermit crab be disturbed in any way. By doing so, this could be lethal for the hermit crab.
7. The leg tips of the hermit crab turn lighter in color, along with a lighter whitish/beige coloring at the joints of the legs and the chelipeds. With some, the outer parts of the legs change to a whitish/beige in color with the very center of the legs and chelipeds having a darker coloring to them.
8. Along with the lighter coloring of the hermit crab’s exoskeleton, if one looks closely where the joints meet, you can at times see where the old exoskeleton is pulling away from the new body. When this happens, the new body underneath can be seen. This reminds me of when a human wears pants., and sits on a chair. You can see the ends of the pants, and usually the socks underneath.
9. When the hermit crab is scooting through the sand in the crabitat, its shell leaves a deep groove type impression in the sand. This dragging of the shell can also be observed when the hermit crab is out of the crabitat in a drip dry area where the shell being dragged along the bottom of the area can actually be heard.
10. When the hermit crab is scooting, its legs are out to their sides as opposed to being in an upright hermit crab style curve when walking. (This reminds me of the stepped-on bug effect look.)
11. When the hermit crab is picked up and it first comes partly out of its shell, one of its front legs stick straight out as though it has no control of it. Within a few seconds, the leg goes into a normal position like the other legs.
12. The premolter spends a lot more time than usual in, or around, the water ponds. This behavior has been observed around the ocean water pond as well as the fresh water pond. With our hermit crabs, it is observed that they frequent the ocean pond more than usual, and the ocean pond will need refilling a few times a day.
13. Some of the hermit crabs get an odor to them. This odor reminds me of the silicone that is put around a tub/shower. Some crabbers have related this odor to iodine, or butterscotch.
14. The hermit crab will attempt to find a secluded area away from its tank mates. Many will go into single hidey areas we have within our crabitats. Smaller hermit crabs have gone into larger extra shells--in their own shells-- where they can hide. This reminds me of a shell plug within the larger shell opening.
15. The hermit crab has slow antenna movement and appears lethargic, or depressed. Unless they are picked up and moved, they remain in the same place they were put.
16. A behavior change is noted. A very shy, out-going hermit crab appears shy, or withdrawn. When it is misted, or bathed, it will not come out of its shell. It is scooting about the tank most of the day as if in search of something. It becomes slightly or overly crabby with its tank mates. I have one hermit crab that never digs, but when in premolt she will begin to burrow.
17. The hermit crab appears to suddenly become uncomfortable with the shell it is wearing. It begins to change shells frequently, but just cannot seem to find that right fit regardless of what shell it has on. This behavior is more frequent than a normal hermit crab trying shells on for fun or entertainment.
18. The hermit crab will begin to dampen or wet the sand regardless of how perfect the humidity level is at the time.
19. The hermit crab will begin to remain about half way out of its shell when it is relaxing, as opposed to being mostly within its shell.
20. The hermit crab will have whitish, cloudy or hazy looking eyes. I have also observed the pupils of the eyes being a dull reddish brown in color as opposed to being the bright, shiny, almost black color.
21. With some of our hermit crabs, it has been their tank mates that let me know that they are in premolt. It would appear that the premolter is all of a sudden a very popular hermit crab. His/her tank mates will surround him/her, or block the entrance to the single hidey that it has chosen to try to seclude itself in. The tank mates stay next to him as though they were best buddies, or trying to protect his friend.
22. A water sac is observed on the hermit crab’s side within the shell. (This may not always be observed.)
23. If the hermit crab is missing a leg or cheliped, a gel limb will form. The gel limb appears to go through a sudden growth spurt the closer the hermit crab is to actually molting.
When I observe any of the behaviors mentioned above, I isolate the hermit crab from his tank mates for its own safety. I have found these to be premolt symptoms with our hermit crabs. This is not to say there are not other premolt symptoms that I have not included in this list, there very well could be, but these are some of the ones I have observed.
If any of these symptoms are noted on your hermit crabs, please act accordingly. It is not always true that a hermit crab will burrow to molt. To date, we have 82 hermit crabs and I have had 319 molts. All of our hermit crabs, C. Brevimanus, (Indo’s), C. Rugosus, (Rug’s), C. Clypeatus, (PP’s), C. Compressus’s, (E’s), have molted above substrate without any attempts of trying to burrow, except for the one Ecuadorian who will begin to burrow when she is in premolt, and will molt within a bottle once she is in isolation. Of the 82 hermit crabs we have, I have four C. Prelates (Strawberry), hermit crabs that have lived with me for over a month and have not yet molted.
Marie Davis (aka ladybug15057)
Photo Credits:
Adam. Photograph by Adam (hermiekid)
Carol of Crabworks. Photograph of the exoskeleton of a C. clypeatus land hermit crab taken in 1999 and used with permission. You can see more photos at http://www.geocities.com/hermit_crabs/carol
Maryanne Ponte's Photo Gallery
URL: http://photos.yahoo.com/peripolak
Mrs Poppy Puff
URL: http://www.mrspoppypuff.com
University of Massachusetts Amhurst: Biology 497H - Tropical Field Biology.
St. John, USVI March 16, 2001 to March 25, 2001 Photo Gallery
URL: http://www.bio.umass.edu/biology/troptrip3/
Vanessa's Crabarium
http://www.aboutlandhermitcrabs.com
Information references:
Charmaine Andrea Huet. Spatial Distribution Of Brachyuran Crabs In Sarawak With Emphasis On Fiddler Crabs (Genus UCA) As Biomonitors Of Heavy Metal Pollution. Institute of Biodiversity and Environmental Conservation UNIVERSITY MALAYSIA SARAWAK 2000
http://www.webcastmy.com.my/unimasresearchgateway/thesis/thesis_0062/chap1.htm
Dunham, D. W., and S. L. Gilchrist. 1988. Behavior. Pp. 97-138 in Biology of the Land Crabs, W. W. Burggren and B. R. McMahon, eds. Cambridge: Cambridge University Press.
Fletcher,W.J. and Amos, M. 1994 Stock Assessment of Coconut Crabs. ACIAR Monograph No.29 32p
Mike Oesterling of the Virginia Institute of Marine Science. Quote relates to blue crabs.
URL: http://www.blue-crab.org/fullmoon.htm
Fletcher, W.J., Brown, I.W., Fielder, D.R., and Obed, A. 1991b. Moulting and growth characteristics. Pp. 35-60 in: Brown,I.W., and Fielder, D.R. (eds), The coconut crab: aspects of Birgus latro biology and ecology in Vanuatu. Canberra, Aciar Monographs 8.
Fox, S. (2000) Hermit Crabs : A Complete Owner's Guide. pp. 27. Barrons Books : NY
Greenaway, P. 2003. Terrestrial adaptations in the Anomura (Crustacea: Decapoda).
In: Lemaitre, R., and Tudge, C.C. (eds), Biology of the Anomura. Proceedings of a symposium at the Fifth International Crustacean Congress, Melbourne, Australia, 9-13 July 2001. Memoirs of Museum Victoria 60(1): 13-26.
Greenaway, P. 1985. Calcium balance and moulting in the Crustacea.
Biological Reviews 60: 425-454. Herreid, C.F. 1969b. Integument permeability of crabs and adaptation
Grubb, P. 1971. Ecology of terrestrial decapod crustaceans on Aldabra.
Philosophical Transactions of the Royal Society of London B 260:
411-416.
Held, E.E. 1965. Moulting behaviour of Birgus latro. Nature (London)
200: 799-800.
Hobbs, H. H., III. 1991. Decapoda. In Ecology and Classification of North American Freshwater Invertebrates. J. H. Thorp, and A. P. Covich (eds.). Academic Press, New York, NY, p. 823-858.
Osterling, M. Moulting and the Full Moon. Online article [URL http://www.blue-crab.org/fullmoon.htm]
Wolcott, T. G. 1988. Ecology. Pp. 55-96 in: Biology of Land Crabs (W. Burggren and B. McMahon, Eds.), Cambridge University Press, New York.
