What makes a good/safe hermit crab shell good and safe? Could you 3D print shells (with the kind of printer that doesn’t leave crevices that collect bacteria)?
Good partly depends on the crab’s opinion - different crab species like different types of shells. I like this guide a lot - http://www.hermitcrabassociation.com/phpBB/viewtopic.php?f=24&t=92552 But purple pinchers, which is the main species you’ll find in North America, like turbos the best. Sometimes you get an oddball who likes babylonia shells or something else, but I have yet to have a crab who’s kept on anything other than a turbo for any length of time. Modified vs unmodified also plays a role, but I haven’t read as much about that as I should, so I’m a little fuzzy on how you can tell the difference for various shells. All I know is that the crabs will modify the inside of the shell to be more comfortable, and sometimes will modify the outside as well - I have seen that one, with chips taken away from the part over their head so it fits more comfortably around their eyestalks & such. The guide addresses it a little, mentioning if crabs will move into unmodified ones or not.
Safe - they shouldn’t be painted, or have any lacquer or anything like that on them. Polished and/or carved shells are fine, as that doesn’t seal any pores or add toxic materials. You want to make sure the shells don’t have holes, since crabs keep water in their shell & holey shells won’t hold water properly. Some chips around the opening are fine & sometimes done on purpose by the crabs, as mentioned.
You also want to make sure they’re boiled when you first get them, to make sure they’re clean. You can use regular water for boiling. I tend to give them a dunking in crab-safe water (treated with Prime) afterwards as well. Sometimes the crabs are more interested in the shells if they have a little salt water in them, so I’ll often do a dunking in salt water as well, and leave a bit of water instead of dumping it all back out.
3D printed shells have been done before, primarily as a way to try & help alleviate the shell shortage facing wild hermit crab populations. For that purpose, I think they’re a good idea, if they’re made with the right materials. After all, they can’t be much worse than some of the stuff crabs are forced into using to cover their vulnerable abdomen. There’s a lot more mixed opinions on using 3D printed shells in my crab groups though - some of the concerns include whether the printing can properly recreate the pores & inner structure of the shell, and how important that actually is for the health of the hermit crab. I haven’t seen any actual conclusions though, mostly speculation. It seems like most people would rather not try & risk their pets’ health on an experiment though. There’s still so much we don’t know about these little guys & how they work.
Oh, and related to the topic & since I’ve been asked before - my groups generally agree that the glass hermit crab shells aren’t a good idea as it doesn’t give them proper darkness when they pull into the shell & that could very well cause stress. The glass ones also wouldn’t be easily modifiable.
