How nasty are Actaeodes tomentosus Xanthid crabs?


New member
I've managed to positively ID my Satanic little hitchhiker as Actaeodes tomentosus Guam.

I'm grown quite fond of the guy, and he's gotten pretty tame at this point, readily taking krill from my hand. As my tank is going through algal succession with different forms of micro, macro, and coraline fighting with each other, I've noticed that the area around his hole is COMPLETELY clean of any macro or micro algae, despite being in a pretty well lit area where I'd expect to see some greenery. I'm not letting nutrient creep too high, so the tank isn't being over-run by algae (save the initial diatom bloom which died back), but there is a conspicuously clean circle going about 4" from his hole in all directions.

This leads me to believe that he's been spending a lot of time snacking on algae. While he happily takes krill, I've never seen him go after amphipods. The other day, he was playing tug of war with a good sized bristleworm over a piece of krill, and all he did was wave his claw at it. There are also a few featherdusters near his home that remain untouched, along with a tiny member of some other sort of Xanthid that I haven't been able to get a clear look at other than its legs and claw.

Could it be that my Satanic looking little crab is actually a pacifist?

I've searched regular google, google scholar, and all the databases at my school's library, but I've been unable to find any anecdotal reports or scientific data about their feeding habits. All I've found in scholarly sources is data about their toxicity, so I'll make sure not to put him in my mouth, not that I was planning to anyways.

I was originally planning on putting him in my refugium, or plumbing a little solitary confinement vessel inline with my system, but given how well he's cleaning up the algae around his cave, I'm wondering if he's actually fairly "reef safe".

Does anyone have any experience with this species, or have any idea what food items they will naturally go after? I don't have any good pictures of the tips of his claws unfortunately, but based on personal observation and what I've seen online, they're surprisingly blunt, actually looking less predatory in form than those on Mithrax crabs, which leads me to believe that he may be more of an algae eater and scavenger than a threat.

If no one has any ideas, I may post this in the Misc Inverts sub-section to see if anyone there has any experience.


Team RC
He is a crab so basically he will eat anything he can get his little claws on. The better question is how much risk you are willing to live with. It sounds like you're attached to him, is he worth the sacrifice of an occasional fish? If yes, keep him, if not to the refugium he goes. A note of warning as crabs grow so does their appetite and their ability to capture live prey.


New member
Thanks for the feedback. I'm having trouble finding info about them specifically, but I know even "reef safe" crabs can go Norman Bates without warning.

I'd eventually like tridacnids, so I'll probably have to move him, I just wanted to get a feel for how big of a threat he is.