Refining the Purpose of Isolation

written by Sue Latell March 8, 2006

2006Hermit CrabsThe Definition of Isolation

Isolation by very general definition, in the crabbing world means to keep crabs separated from each other in groups or by individuals by means of an object such as another tank. It can also mean that one crab can be isolated within a crabitat by an object such as a bottle or CD case, or piece of plastic. The purpose for this division is multiple. Most commonly, isolation has been utilized when dealing with crab illness, contamination, surface molting and more often than I like to see, molting in general. What ever happened to using it for NEW crab introduction? This was at one time, the main reason to have isolation. It was a measure to ensure a crab’s health and stability before subjecting him to competition in a larger population of crabs. This purpose will be my main focus! First let’s address some noted trends.

Current trends in applying Isolation Methods:

1). Naturalized Crabbing

I think that with the more specific advent of “natural crabbing”, we have lost some of the principals of why we practice isolation. Utilizing predatory mites has largely reduced the need to isolate contaminated crabs, and is one alternate method vs. isolation that I think makes sense (if you can afford it). One condition of the newer “natural” crabbing philosophy that I think bears further consideration is with respect to new crabs being introduced immediately into the main tank. While for the most part, it seems less stressful for the new crab to be introduced with a dip in the water dish rather than a bath (I agree with this), the immediate move to better environmental conditions does not allow for the potential issues surrounding PPS. Crabs that may have not been fed properly on their way to you, or crabs that endured severely inadequate heat and humidity, may more easily succumb to the PPS syndrome. This is because we are in effect increasing IMMEDIATELY the level of competition for food and space, while at the same time sticking him in new (if better) conditions for which he is not metabolically able to accommodate due to the lack of those resources. This is hard on the new crab because he more than likely is less “fit” than the existing crabs. A crab that has been deprived of food and water will have a slower metabolic rate making it very hard for him to adjust to a new environment (whether it is better or worse)!

2). Molting

It is with distinct distaste that I continue to hear how Isolation has been bastardized for the sole purpose of weeding out potential molters from some imminent “harm”. Mainly from what I hear (and personally cringe at) from “crazed blood-thirsty cannibalistic crabs”. Truly it is my intent to put to bed this wholly unreasonable belief. Crabs are not cannibalistic in the ordinary course of healthy existence. They are though opportunistic and will eat other dead crabs. I have requested from a biologist who had reported that the cannibalism noted in his field study (David K. A. Barnes; Quirimba Island, Mozambique, 1997) accounted for about 1% of a wild crab’s diet! I have written to him asking if he could specify the circumstances (if it was a molting crab cannibalized or what he constituted as cannibalism). His abstract did not allude to any circumstances. I have sent similar enquiries to 3 other reporters about cannibalism. But note, in each of these articles cannibalism is rated as a food source for less than 3% of the entire wild crab’s diet! As of yet, I have not received replies, and in one case the scientist has retired, and I am trying to locate some of his field assistants. I want this subject addressed! I will be writing an article about it once I have more information.

From the most current diet related behavioral understanding we have to date, if your crabs are cannibalistic, it is a clear indication that population ratios are out of whack with resources (space, food, and to a greater than realized degree, overall dietary components). Crabs specific competition behaviors are often misconstrued as aggression! This general misinterpretation makes crab behavior a fearful thing to identify in objective terms, and therefore hinders us from practicing appropriate solutions. It makes the most important process molting, something to fear. You should not fear it, but know all the related processes that influence molting. So really, there is no good reason to have to move a molter to Isolation unless you are not adhering to proper crabs per tank ratios. If you do not provide a well balanced and diverse diet, this may also potentially increase the likelihood of cannibalism.

I can see the rationale and merit of occasionally having to isolate a crab separately or within the main crabitat during a molt, but not always separate isolation! We should not be mainly fixated on telling people to isolate their crab because they are in danger of being attacked or eaten! While a crab may be consumed by another crab, it is NOT usually because another crab killed it! If we understand more clearly the behavioral habits crabs have, we would be already minimizing this type of occurrence!

Moving pre-molt crabs to ISO is far more stressful than leaving them where they are. Many times I see crabbers question why when they have moved their potential molter, it did not molt, and they want to know whether they should return him to the main tank (NO). Well, to just get to the point, it is because we more than likely arrest them from continuing! This is due to the change in environment. It may seem a subtle difference to you, but the crab if alarmed, will stop producing the molting hormone to switch over his metabolic processes to adjust to the new tank. This may take some time (possibly a week), or perhaps he won’t continue until he thinks his environment is stable; then if he is left alone, he may resume. The unfortunate situation in pre-molt is that it depends on the specific crab’s size and relative health on whether he can re-establish those different processes in a specific time frame we can measure.

I hope you understand what the danger is in moving molters. It is not the most efficient way of dealing with molting issues. I also assert that if we proscribed to a mandatory isolation period for NEW hermit crabs, these aggressive occurrences would become almost unheard of! I plan to outline this plan in detail.

3). Sickness

This is one of the most important reasons to have an isolation tank! It may not be viewed as such since there have been very few diseases or bacteria that have been identified for crabs. Of the most contagious class, there is shell rot. Thankfully there have not been too many occurrences of this. If a crabber does encounter it though, it is imperative to keep the sick crab separate from the main population! If a crab suffers an injury by fall or aggressive encounter, this is also a good place to put them for recovery.

One of the things about refining isolation use is to recognize that within our crabbing community not everyone has the same resources. If we streamline our usage of isolation, we can increase the degree of successful use, and the number of people able to do so by procedure. I have often felt bad for our young crabbers who are hard pressed to supply an adequate crabitat, never mind an isolation tank. With the way we utilize them for molting now, it almost stands to reason that we expect people to have 2 isolation tanks. One for molters and one for sick, injured or aggressive crabs. Again this is something I would like to streamline for better application. I think it is more reasonable and likely to have owners having one isolation tank.

4). Aggressiveness

Some people employ use of isolation for “aggressive” behavior. While not a bad idea in some cases, there is a very varied interpretation of what actually constitutes an aggressive act. This category will improve over time as people become more informed about what constitutes aggression.

Having helped my mother train dogs when I was a teen taught me early lessons in understanding animal behavior. Something I have studied really all my life on various animals. I think this natural interest in it helped me glean some of the finer nuances of what crab behavior is like. We have many kind and gentle animal lovers among us, and for them I think it is the most difficult to see the animal for what it actually is. Hermit crabs do not really have the ability to put “thought” to their actions. They are more imprints of instinctual behavior for a specific purpose. This does not mean that crabs do not have individual traits that make them unique from others within their species, but it is not like a mammal’s “personality”. If they are larger, healthier and stronger than another crab, they will exploit that to maintain their ability to select the best burrowing spot, feeding time, molting area. They use display tactics that warn off other crabs. Their behaviors are of a hierarchal order because they live within a social order. This means that the crabs themselves understand what the displays are about. We don’t always have that same understanding!

Crabs will posture in competitive acts for resources. These are for shells, space, and food. They may even compete for mating privileges, we just are not aware if that is true! In the wild these displays almost NEVER become life threatening, and it is rare for injury to occur. That said most species do not specifically intermingle in the same habitat. They may be found mingling within a niche, but each species will exploit their own areas. So really, when there is an enforcement of privilege occurring, we are really preventing the crabs from behaving naturally if we stop it. Even in inter-species skirmishes I have witnessed, it has never gotten to the point that a crab was hurt. Separation in most territorial disputes will not resolve themselves until the crabs “duke it out”, despite our separating them!

Aggressiveness almost always occurs due to pre-molt hormone imbalance. This imbalance can increase in severity if dietary deficiencies exist. Additionally, if the tank is overcrowded, the crab’s natural tendency to become more territorial during pre-molt may escalate to aggression if there isn’t enough space. If an owner is aware that their space ratio may be at the maximum level, then DO use isolation! Sometimes shell fights become numerous, instigated by a pre-molt crab. Though this behavior is not exclusive to pre-molt, it occurs more often in pre-molt and is incorrectly classified as aggression. As long as there are adequate shells for all crabs, this type of competition is usually minimal.

NOTE- a misinterpretation about pheromone odor on molters:
While it is true that a crab may secrete a pheromone when in molt, it is odorless to prevent detection by predators. While it may be recognized by other crabs of the same species, it would be the “mating” hormone that attracts their attention, and would basically be produced by females ready to mate and still soft. If your molters are housed separately from your main population for the duration of their molt, this would then single out your newly molted crab as a “newcomer” upon reintroduction. Crabs have a strong sense of smell, but their memory is not like that of a mammal. So they will treat the isolated and re-introduced molter as an interloper. We minimize this by utilizing the introductory bathing technique (not to get the “molting” smell off the crab). What I am getting at is that separation is again creating more of a potential for problems, than it is eliminating it!

Why a new approach?

This article is for the purpose of refining, or maybe I should say for redefining what ISOLATION should be used for. I would also like to review what the environmental conditions for isolation should be. And finally, for re-establishing isolation for new crabs and honing the isolation method to aid in reducing PPS type deaths. See “PPS: Minimizing the Impact”. I apologize if I appear to be mocking our current practices; I do realize that some of our crabbers have been able to succeed in the interchange between ISO and main tanks for molters, and I do not want to diminish the bad experiences some of our crabbers have faced. It may be necessary for some crabbers to continue using the isolation method for molters, especially if space and diet conditions are questionable. I have seen and heard that these occurrences still happen though. It seems to me that we just have not resolved this from happening efficiently. I think it is because our approach is wrong, and this is why I am mostly against some practices. Additionally, a good number of other crabbers, including me have not experienced the degree of issues surrounding molters, ever, even though we do not isolate them! So I surmise that it is the behavioral aspects of caring for crabs that we need to exploit to reduce molting related aggression.

I truly hope to swing your attitudes towards really utilizing Isolation methods for applications that will be ultimately of more benefit to our crabs. Let us begin then in refining this method for specific processes that would benefit crabs.

General ISOLATION utilization:

This is what I recommend the priority be for SEPARATE ISOLATION:

  • NEW/PPS crabs
  • SICK or INJURED crabs

A miscellaneous class for:

  • AGGRESSION (true and severe)
  • MOLTING anomalies (deformity, inability to shed, or new molting crabs)
  • MITE CONTROL, where use of predatory mites is not an option.


There are circumstances that can be addressed within the main crabitat instead of separate isolation. This would be done employing the “plastic bottle” method, or some other barrier that is appropriate for use in the crabitat. These would more commonly be related to:

AGGRESSION (territorial disputes, shell fights)
MOLTING (surface molts, ruptured molt sacks, disturbed molters)
DROPPING LIMBS (after initial NEW crab isolation, where crab has been already been moved to the main population from isolation)

Environmental Conditions:

The above divisions were created keeping in mind that there is usually only one isolation tank at an owner’s disposal. Therefore the starting temperature for the isolation tank should be room temperature, provided that it is not less than 72 degrees Fahrenheit. Humidity will be the variable element in this tank and the initial setting will be set at an established starting point based on the reason behind isolation. (These will be defined a little more clearly by class).

NOTE: Heat range is 72 – 84 degrees Fahrenheit.
Humidity range is 74% – 82% (you may have to start below this normal range)
You will be using these ranges as your guide as you increase heat and humidity in the isolation tank up to the AVERAGE range in your crabitat.

The preferred tank type would be glass, but a plastic kritter-keeper that can maintain humidity through use of plastic wrap is also acceptable. (Just harder to maintain) Here is a list of what you should have in the isolation tank:

– Humidity and heat gauges
– Fresh dechlorinated water, ocean salt water
– Appropriate substrate (may have to adjust depth for size of crab)
– Alternate shells of acceptable quality (no holes, not painted)
– Ground cover (plastic or silk plants, driftwood)
– Heat source (by UTH or light)
– Lighting (bulb or tube assembly)-they need 12 hours of light!
– Food (Use mostly natural or fresh food sources)

These items are pretty much utilized the same in your isolation tank as they are in your main crabitats. Now comes the tricky part of changing implementation styles. I was stuck for a while in how to express this with the least confusion and the most flexible usage. The best way I could come up with is to assign heat and humidity controls and isolation duration based on the class (reason) for isolation. Here they are again; in the order of priority isolation should be used:

New Crab induction and method to minimize PPS:

1) Temperature should be in the low range but not so low as to induce hibernation. You want them to eat and access water right away. So the bottom of the acceptable heat range is 72 degrees. This temperature, depending on your household will be very close to your room temperature. If your room temperature is lower, then you will have to use a UTH or light for heat. Over the duration of isolation, the heat will be increased. We are not too concerned about how quickly the heat increases to meet your main tank average temperature, but it should not go over the average of your main tank. You must also have ranges (hot, warm and cool) within the tank, and ocean salt water deep enough for your crabs to easily fill their shells.

2) Humidity is the main worry here. While your crabs may have been in over hot and under humid conditions, you do not want to start humidity too high. This is especially the case if you have rescued a crab that has already lost limbs due to stress or is very sluggish at the pet store. The lower temperature will help him readjust simply because he is not using resources to stay cool. Start the humidity about 10% lower than the normal low limit, so that he will slow down his metabolism that is not overtaxing his system. Keep this level for at least 48 hours. Hopefully he will smell the food and eat. Once he has eaten once, you can begin to increase the humidity every 3 to 4 days at 5 -10% increments. If they bury, do not increase for a day or 2, just to see if they come up. You want the change to be gradual enough that they will continue to eat rather than immediately bury. The more they eat, the more likely they can get their system to adjust.

Here is an example:

Crabs purchased were in a hot tank, no water, just a sponge and sporadic spray bottle misting. They have to the clerks knowledge been at their store for a week. They feed the crabs commercial pellets.

1. You can assume that they are dehydrating. So you will be starting your tank at 72 degrees for temperature, and 60% for humidity. This probably can be achieved by setting up the tank the same day you bring home the crabs. Bathe them in dechlorinated water and then put them in. Have fresh foods in there. Coconut, honey and some fresh form of seafood (shrimp, krill, silverside). These are all metabolic fuel. Do not keep them in the dark. Make sure you keep up a 12 hour light regiment.

2. 3 to 4 days later increase the humidity to 70%. If they remain active and continue eating, you should be able to increase the humidity by 5% hereon. Therefore your next increment will be 70 x .05 = 3.5 so 70+3.5=73.5. You can continue increasing it every 3 or 4 days. Now, here’s the thing. If your crab is fairly large, you should slow down the increase interval. So for this example you may want to adjust the interval to 4 to 5 days instead of 3 to 4. Follow? (I know this will raise many questions) I can’t be more specific, other than to say that the crab is able to adjust metabolically with food as fuel and time. Size does affect the rate of metabolizing, which may mean that they can either do it faster or slower than the rate of change we are using; generally it takes them 72-96 hours or 3 to 4 days.

3. The duration of isolation I have assigned a general 30 day period for. I have done this for two main reasons. The first is that for small to medium sized crabs, the adjustment period is only about 2 to 3 weeks long. All of the adjustments occur within the 30 days. The second reason is that it provides enough time for your new crabs to eat and restore strength while competition for resources is limited to those in the ISO. Also if your new crab chooses to molt within the 30 day window (the most dreaded time) you can keep closer tabs on it! You also have the option to keep them in here longer. This is if they spend too much time buried. They may do so because the increase was too much for their immediate capabilities, that’s why you really do not want to continue increasing the humidity unless you see them eating and moving about on the surface.

Many owners are tempted to move their new crabs to the main population as soon as possible. This is a judgment call owners will have to make. There will certainly be those lucky crabs that had swift transfer from the wild to a caring pet store with satisfactory conditions. If your crab is one of those, by all means do what you feel is best. I personally think it does not hurt to ensure my new ones have the opportunity to “beef” up before facing new competitors in my main crabitats.

Sick or Injured Crabs:

When you have a crab that is “sick” we would qualify this by these conditions, an injured crab should be obvious:

– The crab shows some physical ailment like shell rot (dark scaling on exoskeleton in conjunction with concave depressions in the chitin)
– Listless and inactive outside the norms of what can be expected if he is in pre-molt. (No other sign of molt)
– A crab that is dropping limbs and has been a steady inhabitant in the main tank for more than 30 days

The recommendations I have received from a vet for treating fungal or bacterial infections on crabs is moderate temperature and lower humidity. See “Treating Ailments FAQ”. Therefore the isolation tank can be in the lower to moderate ranges. You do not want to stress the crab from too significant a change so if your main crabitat conditions are typically kept at the higher ranges you may want to do an in-tank isolation until you can adapt the isolation tank to suit the situation.

Miscellaneous Isolation:

Everything else mentioned above except for the named isolation reasons fall here. This is where there is a fine line to be drawn on whether you want the environment to be different than that of your main crabitat. Usually in this category you do not want to vary from the ranges already maintained in your main crabitat. Aggressors that won’t leave other crabs alone and have physically picked up and swung another crab around can be put here. They are most likely in pre-molt and if you move them you may interfere with that process. For this reason, you need to be reasonably sure that this can’t be handled within the main tank. If you feel it is necessary, then try to match the conditions between the two tanks as best as you can.

Well this is the general procedural advice I can recommend. I think there are so many different tank management issues, it is impossible for me attempt to recite them all. I might miss one or stress one more than another and raise too many questions without meaning to. There is just so much surrounding this. If this seems too vague, I did it more out of trying to accommodate everyone’s styles. If you have questions that are specific to what you practice, and you see no referral to them here in this article, I would be happy to address them personally. You can contact me at, and I will be happy to assist you! Please contact CSJ staff for assistance.

Article: Refining the Purpose of ISOLATION ©2006, Coenobita Research

Written by: Susan Latell
Last Edited: 3/09/2006
Copyright © by All Right Reserved.
Orginally Published on: 2006-03-09