Confused by crab sociability

[IvynaJSpyder]

I'm still new to this hobby, so go easy on me, this might be controversial.

So I have been keeping reptiles for years, and one thing that gets drilled into you in that hobby is herps (with a handful of exceptions) are NOT social. They only come together for mating, or to take advantage of a resource.

Crocodiles for example are considering social and often hang around in large groups. They communicate and have a sort of hierarchy, but you wouldn't say they were social the way, say, a herd of elephants is. It's more of a tolerance thing, like "we are all in this together so we may as well get along." Or you'll see groups of turtles basking together on a log, not because they're buddies, but because it's just a good basking place. Turtles will shove each other off to get a better spot and not give a darn.


So what is the deal with hermit crabs?

Reading through this forum the last few weeks I have seen sooo many posts about crabs attacking each other, and the ever-present risk of cannibalization of a molting crab. With any other species if you saw that happening so often, the reaction would be to separate them to prevent conflict. After all, in the wild, a crab would have room to escape another aggressive crab, but even in the largest artificial enclosure that is impossible.

All the care sheets says they're social because they live in colonies in the wild, but is that because they enjoy each other's company, or because they all want to utilize the same resources?

This article here suggests it's the latter- they only hang out in groups because they're waiting for a chance to grab a better house!

"Hermit crabs socialize to evict their neighbors" (It also has a great image showing just how hermit crabs 'remodel' their shells which I never knew!)

Which is based on research from this "Niche construction drives social dependence in hermit crabs"

But in captivity, in theory we can provide a much greater variety of appropriately modified shells for them to choose from, negating the need for this sort of 'social dependence'.

So why is it common practice to keep them in groups? Is there another benefit these papers aren't touching on?

Are hermies kept alone more shy/fearful? Do they not thrive? What is the actual rate of attacks seen with crabs kept in groups? Is it actually pretty rare, or common and just an 'accepted risk'?

I'd love to get more info beyond anecdotal evidence.

[soilentgringa]

I'm still new to this hobby, so go easy on me, this might be controversial.

So I have been keeping reptiles for years, and one thing that gets drilled into you in that hobby is herps (with a handful of exceptions) are NOT social. They only come together for mating, or to take advantage of a resource.

Crocodiles for example are considering social and often hang around in large groups. They communicate and have a sort of hierarchy, but you wouldn't say they were social the way, say, a herd of elephants is. It's more of a tolerance thing, like "we are all in this together so we may as well get along." Or you'll see groups of turtles basking together on a log, not because they're buddies, but because it's just a good basking place. Turtles will shove each other off to get a better spot and not give a darn.


So what is the deal with hermit crabs?

Reading through this forum the last few weeks I have seen sooo many posts about crabs attacking each other, and the ever-present risk of cannibalization of a molting crab. With any other species if you saw that happening so often, the reaction would be to separate them to prevent conflict. After all, in the wild, a crab would have room to escape another aggressive crab, but even in the largest artificial enclosure that is impossible.

All the care sheets says they're social because they live in colonies in the wild, but is that because they enjoy each other's company, or because they all want to utilize the same resources?

This article here suggests it's the latter- they only hang out in groups because they're waiting for a chance to grab a better house!

"Hermit crabs socialize to evict their neighbors" (It also has a great image showing just how hermit crabs 'remodel' their shells which I never knew!)

Which is based on research from this "Niche construction drives social dependence in hermit crabs"

But in captivity, in theory we can provide a much greater variety of appropriately modified shells for them to choose from, negating the need for this sort of 'social dependence'.

So why is it common practice to keep them in groups? Is there another benefit these papers aren't touching on?

Are hermies kept alone more shy/fearful? Do they not thrive? What is the actual rate of attacks seen with crabs kept in groups? Is it actually pretty rare, or common and just an 'accepted risk'?

I'd love to get more info beyond anecdotal evidence.

The only info that you're going to get will be anecdotal for the most part because the majority of people observing hermit crabs in captivity are people who have them as pets.



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[soilentgringa]

I've had over 100 crabs in my home in the last 4 years and have never witnessed an actual attack that I can remember. I've seen kicking and brief instances where one crab was looking at the shell of another but nothing progressed past climbing on and grabbing.

I've never lost a crab to what would be considered or confirmed as an attack, as in there was no definitive proof that another crab was involved in the process.

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[IvynaJSpyder]

The only info that you're going to get will be anecdotal for the most part because the majority of people observing hermit crabs in captivity are people who have them as pets.

Oh I meant more like, other research papers and studies that I don't know of :O Anecdotal is helpful too, just wondering if there was also more like the links I posted.

Like, what *does* happen with a crab kept alone? Do they show significantly different behavior? Do they eat less, hide more? Are they like herd animals that find comfort in a group?

I guess what I wonder is, do we keep crabs in groups because we 'can' without much harm, and not because they have a true psychological need for it?

[wodesorel]

Here's the problem, it is ALL anecdotal evidence, because no one has done controlled longterm studies on the effects of single vs group. And with lifespans of 50+ years, anything that was done would be a snapshot at best.

I've been doing this nearly a decade and I have never seen any solid evidence that they absolutely need to be kept in colonies in captivity. It's something that has been passed down since at least the mid-90s, but whoever first suggested it or why it's been repeated so many times is lost to the early internet. You'll hear "They will die without friends", which at the very least seems like something blown way out proportion, like so many other 'facts' of crab keeping. It has been made to sound so tortuous that no one ever wants to speak up and question it, let alone try it.

My best guess has been that since they are found in the wild in groups, the assumption was made they must need to be with others. Maybe it was bleed over from fishkeeping, where fish found in the wild in schools need to be with others of their kind or they display unnatural behavior and stress themselves to an early death. (For real, but you can observe this easily and there are plenty of warning signs.) I've also always been suspicious that it was a group of keepers giving themselves permission to be a little hoarder-esque in getting as many as they wanted.


There is anecdotal proof that being kept in alone or in pairs results in longer lifespans. Obviously it's hard to gauge quality of life with these guys, but if they are eating, drinking, molting and exploring it doesn't sound any different than ones kept in larger groups. Carol Ormes had Kate for 35 years, and Jonathon is still going (as of two years ago) at 42 years and counting. There was another account of one of the early English explorers bringing one back alone that lived for 25 years. When I handled adoptions I saw many crabs that had been in captivity between 10 and 20 years, and they were all singletons and pairs.

The question that then gets raised is - are these the hardy outliers that had the constitution to survive in the face of completely inappropriate conditions?

I do think caution needs to be taken when it comes to immediately laying blame on other crabs in group situations where attacks are not actually observed - lone crabs do also die, they fall out of shells, drag themselves naked across tanks, decompose into nothing in an extremely short timeframe. All of these things are attributed to other crabs by novice (or simply very upset) owners. At the same time, it's hard to know what happened under all that substrate. That mangled body - was it an attack or did another crab come through after? That empty shell packed with dirt - same as above, or did the crab streak underground and do it themselves?

We also have no good idea about diseases and parasites with these guys. The distributors that harvest them from all over the world just toss them together, which would lead to a sharing of foreign invaders both during warehousing and shipping, and once they are combined at home. Is the fact that they die often when in groups a side effect of passing infections for which some have no natural immunity?

We are also talking about wild caught animals where there is no real way to judge their health or age. How much damage to they sustain in the collection and shipping process? In just what condition are people buying them in? Are they parasite loaded? Is it the effects of group housing, or are they just that sickly that they had no chance of long-term survival? Is it a natural old age death, or one that was exacerbated by being forced into captivity? (Molting requires more energy/resources with every subsequent molt. At some point their stored energy cannot match what is required, which is considered a natural old age death.)

A couple to a few million crabs are imported every year to the US alone. No, not an exaggeration, that figure comes from the distributors themselves - the biggest does over one million by themselves. It makes it really hard to figure out the statistics because of that. It's a minuscule percentage even being cared for properly. Of those, how many are being cared for as singletons or in groups? How many were healthy on arrival? Which ones were the natural outliers? The whole observable situation gets skewed.

That all said, crab on crab violence is a real thing. They are opportunistic hunters and scavengers, they readily cannibalize when the reward outweighs the risk, and they are extremely strong and those claws are not for decoration. When they find another crab in a state where they cannot defend themselves, they will take full advantage of the situation. They are hard-wired for survival, so a perfect meal of crab is always a temptation. A pre-worn shell means it makes an excellent home. They don't have the capacity to understand that their needs are being met and will continue to be met - they are thinking months down the road to times of famine and scarcity. They are resourceful little dudes, it's how they survived for millions of years.
In captivity they seem to only tolerate each other, and they don't interact except when jockeying for the best locations and resources, which as you note with reptiles, people will often misinterpret as 'cuddling' or needing to be together.


It took a lot of self-convincing when I did it - but I have my Ruggie as a singleton. I have lost so many crabs in my colony over the years to situations where I felt it was directly due to the other crabs, that I could not bring myself to take the risk with her in a group. I won't mailorder crabs, so she is likely my once in a lifetime 'exotic'. I got her in April 2016, and she has been picture perfect since. Active, molting regularly, explorative. I see no sign of any sort of stress or her missing the group. If I had space I would like to try with my PPs, I very much regret not having done so with my first and favorite, I keep wondering if he may have still been alive today if I had.

[IvynaJSpyder]

lotta good points

Oh wow, thank you for this perspective! I haven't seen it said much, I guess it really is controversial <_<

I wonder if the 'they need friends!' thing was started by the people selling them? Sell a few crabs to someone, and when one inevitably dies in poor conditions, the owner feels pressured into buying another so their crab still has a 'friend', creating an endless cycle of crab buying. Wouldn't surprise me.

And is there a pressure on crabbers who rescue to rescue as many as possible, I wonder?

With reptile keeping I've seen what some call 'acceptable risk'. For example, using a natural soil substrate vs paper towels. On one hand, there is a small risk of the animal ingesting the substrate and becoming impacted, but on the other, the enrichment of being able to burrow and display natural behaviors can far outweigh the risk.

What I'd love to learn is if keeping crabs in groups also falls under 'acceptable risk'. Do they get something out of it that we can't provide in captivity otherwise, that outweighs the risk of attacks? Or do they do just as fine alone, without the added risk? I guess there's no real way to know beyond long term studies, which as you said isn't likely to happen, soooo @_@

It's still interesting to hear different views on it though!