A Subterranean Terror? Advice pls

[Nireen]

Since you've come to the emergency forum, we know you want a fast answer to your question. In order for us to figure out the problem as quickly as possible, we ask that you answer the following questions as best you can. Some of them may seem odd, but they're all designed to give us the information we need to give you a good solution for your problem. The things in the [ brackets ] are there to make this post easier to read once submitted. Thanks!


1. What kind of substrate is used in your tank and how deep is it?
2/3 Play Sand, 1/3 Eco Earth, mixed with dechlorinated water to sand castle/tunnel consistency. It is 5.5inches deep.

2. Do you have gauges in the tank to measure temperature and humidity? If so, where are they located and what temperature and humidity do they usually read?

2x Analog Gauges (both calibrated and recently checked) one at each end of the crabitat. Current readings 25 degrees C and 88% humidity. Please note: I am in Australia. These temps are pretty much environmental.

I also have a digital gauge that I put in every 2 days whilst changing the food and water, to double check the readings from the analog gauges.


3. Is a heat source used in the tank? If so, what?

I have a large heat mat attached to the back of the crabitat. It is mainly above the substrate but does extend down for a couple of inches. In the warmer months, I don’t have to use it.

4. What types of water are available (fresh or salt) and how is the water treated (what brands of dechlorinator or salt mix and what ratio is used to mix it)?

Fresh water, dechlorinated with locally branded aquarium product Pisces. I use this for my bettas as well. Salt water options are alternated between using marine salt and dechlorinated water and using a Salt Water Conditioner purchased especially for hermit crabs. Observations tell me they prefer the former.

5. What kinds of food do you feed and how often is it replaced?

Foods are supplied according to the Food Pyramid and Safe Food lists as outlined on this site. Cuttlebone is permanently kept at both ends of the crabitat. Forage mix is offered in a separate bowl in addition to their food.

I offer fresh food options, organic dried options and mixes made and purchased from reputable Australian Hermit Crab keepers on Etsy. The types of food are too numerous to list. You’ll have to trust me on this one, LOL. It is replaced every 2 days. I take note of favoured foods. An example is today’s options: peanut, cranberry, egg, carrot, chicken and chia seeds.

6. How long have you had the crab and what species is it, if known?

All my crabs are Aussies. I have had them for a year or so. They were not acquired/added at the same time so precise dates vary crab to crab. (More on this below)

7. Has your crab molted, and how long ago did it happen?

This is the issue. Please see saga below.

8. What type of housing are the crabs kept in, what size is it and what kind of lid is on the housing?

Glass aquarium/tank. 100L. Glass lid with added cling wrap as per humidity level requirements.

9. How many crabs are in the tank and about how large are they?

I am going to add observations of their personalities here as for this dilemma I believe it plays a part. I track and document my crabs movements including their molts so I can always be aware of where they are, what they are doing etc.

Zippy (male) – Alpha Crab, largest. Approximate shell size 3cm. I have had Zippy the longest. He is the most interactive, confident and intelligent. I can set my watch by Zippy’s routines. Although I have observed his role as top of the social hierarchy he is not at all aggressive. Instead he looks out for and seems to protect the smaller crabs in particular Abby and Trinket. Very active crab. Loves to be above ground and adores his food. Has completed several successful molts with me.

Abby (female) – Strong willed personality. Approximately 2cm. Second longest resident. Nearly always found near Zippy. Abby is quite feisty and loves to climb. Has completed several successful molts with me.

Ninja (male) – Newest addition of around 4 months. Approximately 2cm, though slightly larger than Abby. Very different body colour so easy to tell apart. Bit of a loner. He has completed one successful molt with me.

Trinket (male) – Tiny. Smallest crab in the crabitat. 1.5cm max shell size. Very timid. Follows Zippy around. Has completed two successful molts with me.

Vivvy (Gender & status unknown) – 2cm. Vivvy was given to me by a local pet store (shudder) 8 months ago because Vivvy had been attacked severely by their jumbo crab and was ‘unsellable’. Vivvy came to me missing several limbs and very scared. Vivvy dug down the second they were introduced to the crabitat and I haven’t seen them since.

Salty (male) – 2.5cm. Status unknown. Very fast and domineering. Never really played nice with the other crabs but the colony stuck together and Salty would back off so there weren’t any major problems. If Zippy was under molting, Salty was the alpha crab. Salty prefers to be underground. I upgraded my crabitat size at the beginning of the year and at that point hadn’t seen Salty for about 2 months. I moved the other crabs and smoothed the sand. It took days for signs of Salty to be spotted and even then it was just scuttle marks in the sand. After a fortnight, I spotted Salty above ground but Salty bolted for a hole and went back under. It took another week for me to catch Salty on the surface so I could add him to the larger crabitat and let me tell you, he did not like me picking him up! Disappeared underneath the sand in May and I haven't seen him since.

I will also mention Eddy (female), 2cm. Eddy sadly passed away which I will address in the detailed section. Eddy had completed three previous successful molts. Ninja entered the crabitat after the loss of Eddy.

10. How many extra shells are usually kept in the tank, if any?

Currently 20 spare shells in tank of various sizes and types, not including the ones they have taken underground.

11. Have there been any fumes or chemicals near the crabitat recently?

None. I am pedantic. The lid is always on.

12. How often do you clean the tank and how?

Water and food is changed every 2 days. I remoisten surface substrate with spray bottle of dechlorinated water. I have also recently removed and replaced top inch of substrate, checked for mould, bacterial blooms etc.

13. Are sponges used in the water dish? If so, how are they cleaned?

They do have a sea sponge but it is not in the water dish. It is rinsed every two days with dechlorinated water, wrung out and checked for signs of mould. I keep it damp but never wet.

14. Has anything new been added to your crabitat recently?

No.

15. Is there any other information you would like to share that might be helpful (anything that is regularly part of your crab care, playtime, bathing, etc.)?

My crabitat has a second story (made by me) to offer extra space. I got ideas of how to do it with egg crate etc from this website. They have 2x hides, coconut fibre and climbing frames. No metal anywhere.

Since the beginning, I have followed the guidelines outlined by the HCA as closely as I can. I always endeavour to do the best by my crabs and to minimise the risk of cannibalisation etc.


16. Please describe the emergency situation in detail.

Brace yourselves, this is a saga. And a weird one.

The punchline of the saga is that—I am currently dealing with a surface molt. My first ever. I predicted it was coming, so I wasn’t surprised, but I am worried. It’s kind of the culmination of my fears and suspicions.

So where to begin? I have outlined the sizes and characters of my crabs above. To me, this is important because I am hypothesizing what has gone amiss that resulted in this surface molt. Fortunately, I document my crabs' molts, and behaviour, so I have references with approximate dates to go by. I will try to tackle the history chronologically in bullet points before delving into further detail.

May

– Salty goes under, presumably to molt. Hasn’t been sighted by me since.
– Vivvy is introduced, goes underground and hasn’t been sighted by me since.
– Eddy surfaces after a successful molt
– Zippy emerges after a successful molt

June
– Eddy decides to spend most of her time underground, only emerging to eat and bathe. One morning when she emerges, I notice she is missing a leg.
– Mid June, Zippy goes under to molt

July
– I find Eddy without her shell, dead in the water bowl. I was shocked. It was an unexpected, sudden fatality. I replace surface substrate, and check for signs of mould, bacteria etc. None found. Cause of death remains a mystery as does her missing limb. I did not find her severed leg above ground.
– Abby goes under, presumably to molt
– Late July Zippy emerges
– Late July Ninja is introduced to the crabitat

August
– Abby surfaces
– Ninja goes under, presumably to molt

September
– Ninja surfaces
– I notice that shells are being pulled into tunnel openings.

Now is when things get interesting. I knew both Zippy and Abby were preparing to molt by their colour and behaviour.
October
– Early in the month - Trinket goes under to molt
- I notice that a piece of cuttlebone has been pulled into a tunnel opening
– Mid October, Zippy goes under to molt
– Abby goes under 2 days after Zippy

Above ground is only Ninja.

A week and a half later, Zippy emerges. Too quick. His colour is still dull, indicating he didn’t molt. This is odd behaviour for him. He was definitely building a molt tunnel as he filled it in behind him as he went, when he usually leaves it open. He also chose a secluded location.

The next day, Abby emerges. She is still dull in colour. A second crab who I was sure went down to molt has resurfaced too quickly. Abby is missing her defensive claw. It is not visible above ground.

Both crabs are observed eating. They stick together as is their pattern. They are good pals. I presume they will try again but am left wondering what interrupted them both and what happened to Abby’s defensive claw. They built their molt tunnels in very different places, so I don’t believe they interacted with each other while under.

November

- Ninja goes under
- Mid month, Zippy goes under again, in the same spot as last time
- Abbey goes under 5 days later
I breathe a sigh of relief, happy both are trying again.

One week ago:

I come down in the morning and find Zippy above ground. Too quick again. His colour does appear slightly brighter, though it might just be my imagination. Can he molt that quickly? Why would he? He usually takes at least a month.

But there’s more. He is in a completely different shell. This shell is way too small for him, it's almost like he shoved it on in a hurry. I look around for his regular shell and it is nowhere to be found. He has been wearing his regular shell for 6+ months. It’s his favourite and has room to grow. Even if he tries on another shell, he always goes straight back to this one. The only conclusion I can draw is that his regular shell is underground. He has dug himself out naked and put on the first shell he could find. But why?

I offered him a new variety of dampened shells in appropriate sizes and Zippy changed pants. He eats. I am left very confused and concerned. He is not himself. He lacks energy and is very skittish when he’s usually confident.

Six days ago:

Abby emerges. Too quick. She hasn’t molted. She is a pale, pale colour. She crawls to the far back of one the small hideys and faces the wall, like she put herself in a corner. I leave her be.

Five days ago:

Abby still hasn’t moved. I’m concerned. I monitor her as best I can, visibility is hard where she is and I don’t want to disturb her. Zippy is in the hide with her. Sitting, not moving around much.

Four days ago:

I’m doing my routine food and water change. Abby is still in the corner. Zippy is sitting one inch from her looking at me. Curiosity gets the better of me so I break out the torch and peer in at Abby. My heart sinks. Her exoskeleton is sitting next to her shell. I had been worried she would surface molt and she did. My first thought goes to the risk of cannibalisation. Zippy is a lot bigger than her and he is less than an inch from her. I extract Zippy and watch. A little leg flicks out from Abby’s shell. She’s alive! I am so, so proud of Zippy for not interfering or harming her. I move the hidey to a darker spot in the crabitat and wall her off from Zippy (better safe than sorry) with a clear plastic divider. I move another hidey into the main spot and shift Zippy in just in case he is headed the same way.

Over the last three days:

I have monitored Abbey closely. Gradually she is moving more and it appears she has eaten her exo. Phew. Meanwhile, Zippy is growing more active and his colours brighter. He is eating like his usual bottomless pit self and is happy enough with his replacement shell, though he has tried on a couple of others. I think he misses his favourite.

So, it seems, the immediate crisis is averted, whilst the emergency remains. Though I’m still concerned about Abby, the bigger question now is — what the heck is going on? And what do I do about it?

I can’t have crabs surface molting because something is driving them up from underground. I fear for the fates of my other crabs. Both Trinket and Ninja’s time underground is getting a little long for their size. I would have expected them to have resurfaced by now. It can’t be coincidence that the only two crabs I have visual tabs on aboveground (albeit one less a shell and the other less a defensive claw indicating both fought their way up) are my two most dominant/strongest. (I will also emphasise that these two are buddies. Super close. Zero aggression spotted between them. They stick together by choice).

Do I have a subterranean bully who, rather than coming up to eat, is subsiding off cannibalisation? Does that happen? If so, who is the culprit?
It would also explain the shells and cuttlebone that are getting pulled into the tunnels.

The only thing I know for sure is that something is going on down there and I need advice/opinions on the only solution I can think of; to dig or not to dig?

Do I try to find the answer? What if I kill a crab in the process? Should I assume it is just too late for the others?

I can’t have Zips and Abby subjected to this again. I could move them to temporary accommodation but that hardly seems fair on them, they are settled in their home. Besides, then I have a giant, fully functional crabitat that for all I know could be a graveyard or a hunting ground.

Help! I figure I only have the time between now and Zips and Abby’s next molts to solve this.

[wodesorel]

So approaching this as an America who has bad experiences with Ecuadorians who are extremely similar to Aussie crabs in terms of behavior.... you've got 6 fairly larger crabs in a 25 gallon aquarium with 5.5 inches of substrate. (I know their shells are still smaller in size but crab size goes by legspan since they can wear shells either too big or small. Aussies, like Es, tend to err on the side of smaller shells.) With a species like purple pinchers the risk is a lot lower when keeping them in tight quarters just because of the way they behave, but aussies can be active and diggers which ups the chances of trouble.

While there is always the likelihood of a trouble maker being the main problem, I think them not being able to spread out enough is also contributing to the molting issues they're having. Even if one of the crabs isn't purposely going after another, it's easy to stumble across molters accidentally in smaller spaces and then either take advantage of the situation or scare the other crab into moving when they shouldn't.

I would absolutely check the substrate in a few spots as well and make sure nothing has happened underground that is also limiting the comfortable areas to molt. There could be a bacterial bloom or dry areas that they have to avoid. Accidently disturbing a crab shouldn't kill them, but they would need to isolated afterwards until they are moving around normally and eating again.

You may need to isolate molters going forward for safety, if only because there's a troublemaker who isn't stopping. I also wouldn't rule out any crab you see as being buddies as the one causing problems, as hermits just don't have the ability to form friendships like the way we think of it, and what you're seeing could be a form of aggression instead.

[Nireen]

So approaching this as an America who has bad experiences with Ecuadorians who are extremely similar to Aussie crabs in terms of behavior.... you've got 6 fairly larger crabs in a 25 gallon aquarium with 5.5 inches of substrate. (I know their shells are still smaller in size but crab size goes by legspan since they can wear shells either too big or small. Aussies, like Es, tend to err on the side of smaller shells.) With a species like purple pinchers the risk is a lot lower when keeping them in tight quarters just because of the way they behave, but aussies can be active and diggers which ups the chances of trouble.

While there is always the likelihood of a trouble maker being the main problem, I think them not being able to spread out enough is also contributing to the molting issues they're having. Even if one of the crabs isn't purposely going after another, it's easy to stumble across molters accidentally in smaller spaces and then either take advantage of the situation or scare the other crab into moving when they shouldn't.

I would absolutely check the substrate in a few spots as well and make sure nothing has happened underground that is also limiting the comfortable areas to molt. There could be a bacterial bloom or dry areas that they have to avoid. Accidently disturbing a crab shouldn't kill them, but they would need to isolated afterwards until they are moving around normally and eating again.

You may need to isolate molters going forward for safety, if only because there's a troublemaker who isn't stopping. I also wouldn't rule out any crab you see as being buddies as the one causing problems, as hermits just don't have the ability to form friendships like the way we think of it, and what you're seeing could be a form of aggression instead.

Hi, Thank you for responding, I appreciate it. This situation has me quite stressed because I am very attached to my crabs. I didn't know that Aussie crabs have behavioural similarities with the Ecuadorians and I'm sorry to hear you have had bad experiences with them in the past.

The idea that they might be overcrowded is disconcerting. If they are colliding tunnels down there it would certainly account for the disturbed molts. I didn't know that Aussies as a sub-species might need more space due to their active natures. I would hate to think that I have unwittingly caused this problem.

When figuring out how many crabs I could house, I used the HCA guide for calculating minimum tank requirements and then added buffers to allow for extra space just in case. Pretending they all fall into the small category of a 4cm legspan (which only Zippy does the rest are smaller) they require a minimum of 9.5L of space each. 6x9.5L=57L. Extra space in crabitat 43L. Their substrate is deeper than minimum suggestion too and I added a second story because I wanted to utilise as much space as possible and give them the chance to escape from each other if need be. So, if they are cramped, I'm really not sure how to fix that moving forward. Add more substrate?

On the plus side, I think I may have over-estimated the size of my crabs in my emergency post. Zippy is by far my largest (he dwarfs Abby & Trinket) and he is currently sitting in a compartment of the food dish that I measured at a 3cm diameter. He fits in, shell and all with room to spare. Admittedly he is not stretched out, but it shows that his shell is not 3cm as I first thought. My crabs really are small. If I can figure out how to attach a photo I will.

I have poked test holes with a kebab stick into the substrate to check for strange smells, colourations, dryness etc. I didn't notice any causes for concern but with the wet/dryness it's hard to tell. Through the glass sides, I don't notice any colour changes between the damp surface sand and below. Is there a better way I could be checking? How do I check thoroughly without digging?

I have thought that I might have to employ a molt tank for safety in the future. It is just going to be hard to intercept on cue.

Yeah true, it's one thing to perceive them as friends, but I wouldn't want to stake too much on it, hence I walled off Abby the second I knew it was a surface molt, LOL.

Most of my deductions on who is potentially guilty are based on good ol'fashioned process of elimination. I look at who was above ground when incidents happened, therefore wasn't to blame. For example, Zippy. Zips rarely digs. He likes to be aboveground and I can nearly always see him. If he goes under, it's to molt. Also, if he wanted to take advantage of the situation and go after surface molting Abby, he could have. She was vulnerable and right beside him. Easy prey. But he showed zero interest. Ninja was also aboveground the entire time when Abby went under and emerged missing her defensive claw. He was climbing and primarily on level two in that time period. Trinket just doesn't have the size to be my culprit. I don't imagine a tiny crab could get the better of a much larger one, but please correct me if I'm wrong, it would be interesting to know.

If I had to put money on it, I'd say it's Salty and that things for poor Vivvy look grim.

On a very positive note -- Ninja emerged today! Phew. All legs and claws accounted for, shell intact and his body is brightly coloured. All signs point to a successful molt. Wherever Ninja chose to build his molt cave, it wasn't discovered.

Long term, I'm still stuck. Crabs are going to dig and whatever is going on down there is still far from ideal. It is so frustrating not being able to see what is happening beneath the sub. I have two crabs I haven't seen since May. Is it possible they are still alive or am I kidding myself?

Sorry for all the questions, but I'm an overthinker and I really needed to bounce ideas and concerns off fellow-crab keepers.

Thank you again.

[Nireen]

Pic for size approximation. Zippy, my largest crab. The indent he is sitting in measures 3cm in diameter.

IMG_20221205_175123 by Nireen D, on Flickr