Mine loved escargot and walked around with a clownfish which it caught with its claws from the underneath of the belly. This is likely because there is very little uneaten food in my tank, so when push comes to shove.
Crabs are certainly OK for those who possess the knowledge of which are good and which are not, I hoping many of us would agree that most will eat what they can catch. In any event, I want my tank inhabitants to thrive and not have to be concerned about marauders, and after more than a decade, I still am not sure.
Maybe the ban is unwarranted, but it's appears to work for me.
I think the main issue is people keep too many of them. I have maybe 7-8 hermits ( 4 red legged and remaining blue legged) and one emerald crab in 150 gallons. They bother nothing but algae. But crabs are opportunistic and if they starve, what do you expect them to do? I would also eat a lot of things I would normally not want to eat, if I was starving
. For instance, although reef safe, tangs can also develop and appetite for corals if they are not fed enough.
I think crabs do some essential work in a tank that no other inhabitant can do. Emerald crabs are terrific algae eaters and are capable of removing hair and bubble algae that snails and fish cannot remove. Their claws allow them to rip algae from thigh crevices that snails and fish cant reach. Hermits are dual function in a way that they can eat both algae and detritus. They are also very good at keeping the sand white. My red legged hermits spent most of their time cleaning the sand and tuning it over. Most snails for instance wont touch any complex filamentous algae of any kind unless it is mown down, they like film algae or algae that is mown down. You need hermits (or emrald crabs) to mow down the filamentous algae for snails to scrape of the remaining base.
Another benefit I encountered is; hermits flip snails that are stranded. Yes, strange as it sounds, I have seen in multiple occasions that hermits will flip an upside down snail. They probably do it to check out the shell or to check if something is under the shell (since they also move around small pieces of rock to check under), but end up flipping the snail back on once they realize there is something inside.
If you check the claw shape of reef safe crabs like emrald and blue or red legged hermits, they all have spoon tipped claws. Those claws are ideal for eating algae, they are less than ideal for catching anything that can move. It would be like trying to cut a raw steak with a spoon.
For hermits another important factor is available shells. Just because there are empty shells dont mean hermits will like them. They have certain preferences when it comes to choosing shells. So it is important to keep a verity of different shells. Some wont use shells other than what they are looking for. For example, in the ops case, I think the crab he has is something like a halloween hermit( since that is one of the few thumps sized hermits and not reef safe), which wont use anything but conch shells. In the same way, some prefers conical shells while other like round shells. I probably have at least a hundred shells laying around the tank, remaining from the snails I have kept over the years. I have never removed a snail shell from the tank and since I have a breeding population of snails there are many shells.
Imo, nobody needs 1 hermit per gallon or per 2 gallons or even 5 gallons, unless you are going to specifically feed them. You would need no more than 1 hermit per 20 gallons and for emeralds it is perhaps one for 40 gallons.
