Digging Habits

[tnyfootprntz]

Back in mid-April Hermit Dave started a thread that got me thinking about whether hermit crabs in the wild dig under roots or not. For more insight I thought I'd email Tammy at the Crabbage Patch and see what she thought, since she has a large outdoor set-up for her crabs. I wrote: "A while back we were discussing, at land hermit crabs.com, some crab deaths that we thought might have been the result of collapsed tunnels in the substrate. I was wondering if crabs in the wild choose digging locations that contain structure, such as roots, large rocks, etc. or if they prefer to dig where the soil is loose and unobstructed?"Here's what she wrote:-----------"I have noticed with all of my crabs that when they bury to molt, they tend to choose more protected areas in which to bury. For instance, under food and water dishes and along the perimeter of my cages (which are long outdoor cages so that crabs can bury into the natural Florida sandy soil to molt).They seem to instinctively feel safer burying near or under structures since these structures would provide greater protection from anything possibly walking above them which could crush or kill a hermit crab that is in the process of molting . Loose substrate is probably preferred, but as long as they can "pack" an airspace in which to move about and breathe during the molting process, that seems to be most important. I have tanks in my flea market booth that I have set up with deep, moist sand (which varies from 4 inches for tiny crabs up to 12 inches for Jumbo crabs to illustrate the importance of providing crabs with the proper substrate type and depth to allow them to bury into complete darkness in order to promote the Molting Hormone (MH) to be secreted properly. I usually keep the substrate in these tanks "sand castle making consistency" (even though my crabs come up on Saturday morning and back home the next evening on Sunday) so that I have things set up properly but occasionally my sand will dry out. Normally on Sunday morning many of my Tiny and Small crabs are completely buried ready to sleep for the day since they've been there overnight. However when my substrate has become too dry...I have noticed that hardly any crabs tend to bury overnight. This would indicate to me the importance of providing moisture ("sand castle making consistency" so they can pack an air space within their molting cave or tunnel) at all times so that crabs tunnels (air space) don't collapse suffocating or trapping them before they have had a chance to fully harden up and resurface."-----------I also asked what was the greatest depth she had known a crab to dig down to. Her reply:-----------"I have a special cage that provides my crabs with the the ability to bury down into 36 inches of sand and on several occasions I have heard crabs (jumbos?) scratching at the very bottom of the cage. I think that when given the opportunity, they will tend to bury fairly deep into the earth as a means of protection."------------And in the second email, Tammy writes:------------"You are certainly welcome to quote my email ( including this one if it is helpful). I went back and re-read it and am not sure it answered your question very clearly.I do agree that hermit crabs tend to initially prefer to choose areas that have some sort of structure (such as under a rock, under water dishes, near the base of plants and along the perimeter of my outdoor cage as well) as opposed to more open and seemingly vulnerable areas. I have also found that they will bury very deeply when given the opportunity to do so most likely for additional protection from possibly being walked upon or crushed when they are soft and vulnerable. They tend to tunnel quite frequently and may end up coming back up from molting several feet from where they initially buried. I really feel that moist, deep substrate is the key when trying to replicate the molting conditions of crabs in the wild since they have to create a dark, protective burrow underground with an air space in which to move about and breathe during the molting process. At times when I've become impatient and dug up my pet jumbos at the 3 month mark...I have found that their "cave" has become almost encapsulated. That was one way that I could tell that I had come upon their underground burrow, they had packed the sand in a way to create a hard outer protective shell. It actually took effort on my part to break through the hardened walls."-----------We may never know exactly how a crab in the wild digs, but I'm now leaning against the root theory I had earlier, because a pre-molt crab might be wasting energy trying to break through roots. I'm thinking depth is what a crab is ultimately after, at least when molting. And the ability to mold a nice chamber with air space all around.I realize that we're aware of the importance of good moist substrate, but I thought I'd share this because I think it can't be over-emphasized. I'm grateful to Tammy for taking the time to let me pick her brain.

[tnyfootprntz]

You're welcome The challenge to provide the perfect substrate conditions is always a puzzle to me. My crabs seem to be molting o.k., for the most part, but winter heating methods make it hard to maintain moisture all the way through. I lost some crabs in January, and can't help but think it was due to patches of dry soil. I was thinking about burying some terra cotta pots or pieces of broken ones, which might help retain moisture a bit longer. But not sure if I want to obstruct their digging space like that. I'm always glad when spring/summer arrives so I can get rid of the heat lamps for a while.

[Nicole]

Thanks for posting this Sue! That's fascinating to see how deep the crabs will actually dig, given the chance. I had always wondered about that since they seem to dig down to the bottom of the glass every time. I wonder, too, if a lot of crabs get trapped underneath the surface naturally and don't come back up. Would Tammy's jumbos (the ones that she got out) have resurfaced on their own?

[tnyfootprntz]

I was wondering that too. I think that the little rooms they create for themselves allow them to stay under as long as necessary, until they have the strength to dig all the way to the surface. But the conditions within a crabitat (drying substrate, other crabs digging too close, humans poking around with water and food bowls, etc.) hinder both the crab's preparation of the molting chamber as well as the crab's own timeline for when he's ready to resurface.

[Crabby Abby]

Just something interesting I noticed to support the theory that crabs prefer to bury near items that provide support to the substrate. I keep a supply of 6 shells in the tank of 2 ISO'ing crabs. In the 3 1/2 weeks I've had them, the smallest crab has buried in various spots around the tank and each time, nearly all of the shells are buried to varying depths on his right and left around him. Today it will be the left end of the tank and without me doing anything, when he moves spots, I'll find the shells have been moved too.

[tnyfootprntz]

That is interesting. Stuff gets buried in my tank a lot, I always assumed as an accidental result of digging. I used to keep an aquarium ornament in the tank - it's a goofy looking fish figurine that always makes me laugh. I would put it on an upper level but it always got knocked off. Then it would mysterioulsly begin sinking into the substrate, until all I could see of it was one googly eyeball. We joked about it, I would walk by the tank and it seemed as if that fish was staring at me with that one eye, pleading, "Save meeee!"