The Care and Keeping of Marine Hermit Crabs

Donya Quick

The Care and Keeping of Marine Hermit Crabs

The Care and Keeping of Marine Hermit Crabs Donya Quick [Working Draft v1.10, 05-May-2011]

Copyright © Donya Quick, 2011. All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system, without permission of the author.

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Donya Quick

The Care and Keeping of Marine Hermit Crabs

TABLE OF CONTENTS Introduction......................................................................................................................... 3 Myths Surrounding Marine Hermit Crabs .......................................................................... 4 Frequently Asked Questions by New Hobbyists ................................................................ 6 Care ..................................................................................................................................... 9 Marine Aquarium Basics .............................................................................................. 9 Types of Aquariums Suitable for Hermit Crabs ......................................................... 20 Macroalgae.................................................................................................................. 24 Livestock Acclimation ................................................................................................ 26 Diet.................................................................................................................................... 28 Suggested Foods ......................................................................................................... 29 Molting.............................................................................................................................. 30 Common Community Tank Problems .............................................................................. 31 When Hermits Aren’t to Blame .................................................................................. 31 Compatibility with Snails and Other Sessile Invertebrates......................................... 33 Compatibility with other Hermit Crabs ...................................................................... 34 When Hermit Crabs Really Are Unruly Animals Bent on Destruction...................... 36 Signs of Impending Doom and Recommended Solutions .......................................... 37 Species Identification........................................................................................................ 39 Anatomy and Terminology ......................................................................................... 39 Species Descriptions ................................................................................................... 40 Notes on The Small Clibanarius Species .................................................................... 63 Claw Morphology and Adaptation.................................................................................... 64 General Claw Types.................................................................................................... 64 Claws in the Aquarium ............................................................................................... 67 Behavior............................................................................................................................ 69 Behavioral Vocabulary ............................................................................................... 69 Dominance Hierarchy ................................................................................................. 71 Introduction of New Individuals................................................................................. 71 Courtship Behavior ..................................................................................................... 73 Reproduction..................................................................................................................... 74 Injuries and Health Concerns............................................................................................ 75 Missing Limbs ............................................................................................................ 75 Soft Tissue Injuries ..................................................................................................... 75 Physical Abnormalities ............................................................................................... 76 Molting Complications ............................................................................................... 76 Oxygen Deprivation.................................................................................................... 78 Exposure to Toxic Substances .................................................................................... 79 Desiccation.................................................................................................................. 79 Swollen Abdomen Syndrome ..................................................................................... 80 References and Recommended Reading........................................................................... 82

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The Care and Keeping of Marine Hermit Crabs

Introduction The bulk of the hermit crab-specific information in this document is based on my own experiences, research, and observations of hermit crabs both in the wild and in aquaria. When I discovered the remarkable lack of reliable species information, I took the approach of picking species and observing them primarily in captivity, since I have not had as many opportunities to examine species in the wild as I would have liked. In time I may be able to remedy that. Some of the information in the basic care sections can also be seen elsewhere on the web and in other books, since it is common knowledge in the marine world – the sort of knowledge anyone can acquire given enough time to proceed by trial and error. Still, the more commonly available information on marine hermit crabs rarely goes beyond stating the minimum requirements for the survival of hermit crabs in community tank and tends not to address the needs of individual species or what makes a good species tank. I have attempted to adapt the care information to hermit crabs specifically while including species-specific requirements where applicable. I have also focused primarily on concerns that are most pertinent to moderately sized and smaller tanks. In a wall-sized tank, many of the compatibility issues discussed here become less relevant, since there is enough space for small animals to successfully avoid each other. The care information here should not be uniformly generalized to all tanks, particularly those containing corals, which have far stricter environmental needs than hermit crabs. Hopefully the observations I have incorporated into this document will shed some light on the behavior of hermit crabs in captivity in ways not represented elsewhere, and provide a view of them as interesting animals in their own right rather than simple additions to a tank’s janitor squad. I also encourage anyone who is new to the hobby to seek out multiple sources of information and not treat a single source as a stand-alone reference. Knowledge changes over time, and it is an aquarist’s responsibility to keep up with those changes. [Work in progress – additional sections not included in this version]

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The Care and Keeping of Marine Hermit Crabs

Myths Surrounding Marine Hermit Crabs The following are some well-distributed myths regarding marine hermit crabs and their care in captivity. Many experienced marine hobbyists will find at least some of these myths absurd – but I have heard or read each of them on numerous occasions in the last several years. The ideas are accepted by just enough people to seem plausible to someone who lacks the necessary information to debunk them, resulting in continued propagation over time. Some of the statements reflect ignorance of advances in the understanding of small-scale marine systems, and others are due to confusion regarding species requirements and the biology of hermit crabs in general. Myth #1: marine hermit crabs cannot survive in captivity and should never be kept. I’m still not sure how it came to be that certain communities of people hold this view, particularly while some of them understand that terrestrial hermit crabs can be kept without issue. I suppose it’s possible that this myth had an element of truth to it back when marine aquaria were a new frontier being explored. In modern times, however, the only significant remaining hurdle is the replacement of wild-caught hermit crabs in the trade with fully captive-bred strains. It is worth noting that this hurdle also remains for many fish in the aquarium trade as well. Myth #2, version 1: marine hermits never need access to land. Version 2: marine hermits always need access to land. Clearly both can’t be right at the same time. Both are also false when applied uniformly to all hermit crabs classed as living in marine environments. Pay attention to where a given species comes from. If it comes from a reef that’s quite far away from land, odds are it’s not going to need to be out of the water constantly. If it lives on a beach and spends a significant amount of time out of the water preferentially, you may need to be more creative with the tank setup and accommodate some land access if you don’t want your hermit crabs to get too curious about climbing power cords and other tank equipment. This is addressed in more detail in the sections on hermit crab care and species descriptions. Myth #3: you shouldn’t handle your hermit crabs, because it’s bad for them. It makes sense to advise someone not to handle hermit crabs that are large enough to be a hazard to fingers, although that would fall under “you shouldn’t handle your hermit crabs because it’s bad for you.” It also makes sense to discourage small children from handle hermits because of the risk of the animal being injured if dropped. A good fall can stun or kill a hermit crab (a tactic some seabirds use in the wild). Handling is an important part of inspecting hermit crabs to identify the species and to ensure that they’re healthy, especially in tanks where the hermits may not be easily visible on a regular basis. Although you don’t need to get cuddly with them, there is certainly no harm done in picking up a hermit crab by the shell and holding out of the water for a couple of minutes to give it an inspection. It is up to the handler whether to 4

Donya Quick

The Care and Keeping of Marine Hermit Crabs

allow the hermit crab to walk around on his/her hand if it is willing – bearing in mind that doing so can result in some unwanted nips if the handler isn’t cautious. Some hermit crabs, even small ones, think human skin is rather tasty and also have the ability to snip small pieces off. That fact may open up the possibility for a novel approach to the removal of unwanted calluses, but it also means that larger species should be handled with care (or sturdy gloves that don’t smell like anything edible). Myth #4: hermit crabs are social and need friends to be happy. This idea is probably related to terrestrial hermit crabs, of which some species exist that live in groups peacefully. In fact, some terrestrial (and marine) hermit species can be kept in quite dense populations. These species exhibit some characteristics of social animals, although the word “social” is often taken too anthropomorphically by pet owners. Regardless, tolerance of other individuals is not uniform across all hermit crabs. Some species definitely do not enjoy the presence of others in the small space of an aquarium, and crowding will result in a hermit crab war with a high casualty rate. Calcinus seurati is a good example of one such species. This is addressed in more detail in the section on species descriptions. Myth #5: you should never help or disturb a molting hermit crab. Well, this isn’t so much a myth as something I’ve found to be a gross overgeneralization. Most of the time, it is true that meddling with a molting crustacean will do more harm than good. It is also absolutely true that anyone lacking in steady hands or a thorough understanding of the anatomy of the molting animal will do more harm than good unless extraordinarily lucky. However, when applied to all cases involving all people and all hermit crabs, it’s a bit like the myth that you will somehow harm a baby bird for life by assisting it if it gets stuck when hatching. Is it possible to harm a molting crustacean? Most definitely, particularly if one is careless. Is it possible to stress a molting animal into doing something that causes it to injure itself? Absolutely. Is it possible to safely save a crustacean from a bad molt that would otherwise significantly harm or even kill it? Indeed. Any disturbance during molting will add some stress. The question is whether the stress from disturbance will be less than stress from none, and animals that are regularly handled will be less likely to have a violent reaction to intervention than those that have experienced little human contact. The success rate isn’t very high for saving a bad molt in the most serious cases, since a really bad molt usually has a deeper underlying cause within the animal (old age, physical weakness due to other causes, etc.), but the success rate for all cases isn’t zero. When the hobbyist is experienced and intervention will clearly make the difference between a healthy animal and either a dead or cripplingly deformed animal, there is nothing wrong with lending a helping, extremely careful hand. Still, this kind of action is never territory for a novice. Molting complications and assisted molting are covered more in the section on health concerns. Myth #6: small hermit crabs are herbivorous and are great at cleaning up algae. Hermit crabs are omnivores. They will eat algae sometimes, but will not eat all types and are not purely herbivorous. The rock-cleaning behavior that is commonly

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The Care and Keeping of Marine Hermit Crabs

pointed to as algae removal largely consists of sampling what gets pulled off of the rock and discarding the majority of it. If something tasty comes along, it will certainly be eaten, but the rest will be ignored and sent up into the water column in a plume of debris. Although at a glance the algae may appear to be gone, it has probably just been shredded and will likely re-establish itself elsewhere in the tank if the nutrients allowing it to grow aren’t eliminated. Some of the algae might be eaten by the hermits if there’s not much else to nibble on, but tankmates may also start to look tasty if there is no other food available. This is addressed in more detail in the section on diet for hermit crabs.

Frequently Asked Questions by New Hobbyists How does a hermit crab grow? Hermit crabs grow by shedding their old skin and forming a new one. See the section on molting for more information on this process. As hermit crabs grow, they require new shells to move into so that their soft bodies can stay protected, as they do not grow their own shells. Strangely this process of molting and needing new shells seems to cause confusion for lot of confusion among non-hobbyists and new hobbyists over how both hermit crabs and snails get bigger shells. Many times I have heard and read questions about where snails get their shells and whether they need new ones to grow into like hermit crabs. Both animals do have the similarity of wearing the same shells, but snails grow the shells. Hermit crabs just make use of it after the snail is dead. My hermit crab is missing limbs! Will it get them back? Yes, assuming that the environmental conditions are suitable to allow it to molt successfully. Crustaceans re-grow lost limbs at each molt, although the new limbs may not be the same size as the others until a few molts have happened. I found the front half of my hermit crab drifting in the tank! Is it dead? Probably not – most likely the hermit crab just molted and you are seeing the old skin. It’s common to see only the hardened exoskeleton, since the covering for the soft body is thin and disintegrates easily. However, you can check whether it was just a molt by following the steps in the next answer. How do I know if a limb or body is just the old skin from a molt? When the old exoskeleton is shed, it is hollow. If you see the entire front half of a hermit crab, you can check whether it is from a molt by picking it up and lifting the carapace. If it’s completely hollow inside and joints are still held together by thin tissue, the hermit molted. Sometimes corpses from long-dead hermit crabs may become hollow after scavengers have eaten them away, but these usually fall apart and are foul-smelling. Occasionally limbs may get stuck during molting and will be seen floating around the tank afterwards. These will not be hollow when examined, but do not necessarily indicate a dead animal. If you see the entire soft body that is usually hidden in the shell, then it is the corpse of a dead hermit.

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The Care and Keeping of Marine Hermit Crabs

My hermit crab disappeared! Where did it go? If the shell is missing too, it probably disappeared because it molted and is hiding for safety. When crustaceans molt, they remain soft for some time afterwards. During this time, they are vulnerable to predators and may hide as a result. If all shells are accounted for and no hermit crab can be found several days later, it is possible that something else in the tank ate it. This is again common during molting, since soft, newly-molted crustaceans are quite vulnerable to attack from otherwise harmless animals. Finally, if the tank is open-topped, you should also check the surrounding area for an escapee. It’s not impossible for hermits to escape by climbing up power cords and airline tubing. If they fall out, they can dry out rapidly. Don’t assume that a dried out crab is dead – put it back in a cup of tank water and see if it reanimates. See the section on desiccation (under injuries and health concerns) for additional information. I don’t like the shell my hermit crab is living in. Can I make it change shells? There is a difference between “can” and “should” in this case. There are ways to force hermit crabs out of their shells, but they put the animal at high risk of injury. If your interest is in keeping the animal alive and healthy rather than extracting it for preservation as a dead specimen, then leave the hermit crab alone to make its own shell choices. You can try offering other, prettier shells, but if the hermit prefers the old, yucky shell, you’ll just have to live with its decision.

I brought a hermit crab home from the beach in a bucket of water. Can I keep it? If you don’t have an established marine aquarium ready for it and have no experience in keeping aquariums, the answer is always NO. Never collect an animal unless you already have the necessary equipment in place to care for it. If you do not have an appropriate setup to care for the animal and it has not been exposed to non-native species (for example, if it has only been in a bucket of water from the same site), take it back immediately and replace it where it was found if it is legal to do so. However, you should NEVER re-release an animal if either of the following two conditions apply: 1. You are too far away from the point of collection to return the animals. NEVER release it onto a beach in another area. 2. The animal has been placed into contact with non-native fauna. This includes other animals, water, plants, rocks, and substrate that have been collected from the other areas or purchased from a store. In either of these cases, re-release is risky since it can introduce non-native species (even at the microscopic level). If either condition applies or it is illegal to rerelease animals in the area of collection, it is far better to take the animal to the nearest pet store with a marine department. Most marine fish stores will happily take animals in these situations.

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The Care and Keeping of Marine Hermit Crabs

On the other hand, if you do have a marine aquarium already set up, there are two main considerations. First, if you don’t know what species the animal is, you may be inviting disaster on your tank if it isn’t set up to be a species tank. Second, as already mentioned, you can’t always just put the animal back where you found it and may need to either place it in its own tank or give it to a pet store. If you have prepared for both of these scenarios and the animal was legally collected (some regions require permits for collecting hermit crabs or may forbid invertebrate collection completely), then you probably have little to worry about.

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Donya Quick

The Care and Keeping of Marine Hermit Crabs

Care Compared to other marine animals, hermit crabs are not terribly difficult of animals to care for, but only for those with some experience in aquarium keeping. To the complete beginner, no marine animal is on the same level of difficulty as a hardy freshwater fish. Although some, specialized freshwater systems can be quite complex, the majority of marine systems are more complicated than their freshwater equivalents in terms of equipment requirements, chemistry considerations, and required knowledge for success.

Marine Aquarium Basics Although it is possible to start a marine aquarium with no prior experience in aquarium husbandry, it is usually discouraged by knowledgeable aquarists unless the hobbyist in question is willing to invest a large amount of time doing background research on marine aquariums and proceeds slowly with setting up the tank. Even so, it is usually much simpler with a smaller risk of catastrophic events to spend a year or two dabbling in the freshwater world before considering a marine aquarium, since marine aquariums are, with few exceptions, more demanding than freshwater aquariums in terms of required knowledge and maintenance. For that reason, this section will be approached with the assumption that the reader already has a basic grasp of freshwater aquarium principals such as tank cycling and water chemistry regarding pH, kH, ammonia, nitrite, and nitrate. These topics will each be touched on briefly, but a reader encountering these terms for the first time should seek out additional information beyond this document.

Chemistry The primary chemistry factors in a freshwater aquarium are pH, kH, ammonia, nitrite, and nitrate. These are also important for marine aquariums, with the addition of some new parameters to monitor, namely salinity (measured via specific gravity). Some marine animals, such as corals, make having test kits for calcium, magnesium, strontium, and other trace elements worthwhile, but for less-sophisticated marine tanks it’s usually not a consideration. For a hermit-crab only tank, test kits for elements like calcium and magnesium are only really useful as diagnostic tools (and are rarely needed even then). The following are some good guidelines for water parameter ranges that will be acceptable for hermit crab species tanks:

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Parameter pH kH Ammonia Nitrite Nitrate Salinity* Specific gravity*

The Care and Keeping of Marine Hermit Crabs

Range, as readable on a test kit 8.0-8.4 8-12dkH or 143-215ppm 0ppm (level undetectable) 0ppm (level undetectable)