How big a crab is a threat?

[Luananeko]

I've been slowly but surely catching every hairy crab I find ever since I finished putting my TBS live rock in last month, but there's a few that keep evading me and ignoring my traps. One of them appears to have reached its adult size with its carapace around 1/2" wide. I haven't added any fish yet since I wanted to get rid of the pest crabs first, but I'm starting to wonder if I'll ever get to that point.

Is a 1/2" crab a threat to a watchman goby and a firefish? Those are the first two fish I was planning on adding... I'd hate to add them only to have the crabs make a meal of them. I know the crab isn't reef safe, but my tank is going to be FOWLR other than the cup & tube corals, sponges, and such that hitch hiked in. If he's not a threat to the fish, is my CUC the only ones at risk?

I've also seen an 1" long pistol shrimp hiding under the rocks as well. I assume he wouldn't be an issue (in fact, he may even pair up with the goby)?

 

[Flippers4pups]

I've been slowly but surely catching every hairy crab I find ever since I finished putting my TBS live rock in last month, but there's a few that keep evading me and ignoring my traps. One of them appears to have reached its adult size with its carapace around 1/2" wide. I haven't added any fish yet since I wanted to get rid of the pest crabs first, but I'm starting to wonder if I'll ever get to that point.

Is a 1/2" crab a threat to a watchman goby and a firefish? Those are the first two fish I was planning on adding... I'd hate to add them only to have the crabs make a meal of them. I know the crab isn't reef safe, but my tank is going to be FOWLR other than the cup & tube corals, sponges, and such that hitch hiked in. If he's not a threat to the fish, is my CUC the only ones at risk?

I've also seen an 1" long pistol shrimp hiding under the rocks as well. I assume he wouldn't be an issue (in fact, he may even pair up with the goby)?

Sounds like a gorilla crab. They can be predatory towards small sleeping fish and some corals.

 

[alton]

I have been told pistol shrimps from Florida do not pair up. But they are not a threat to other fish either. As long as you do not mind the popping noise they make

 

[Luananeko]

Sounds like a gorilla crab. They can be predatory towards small sleeping fish and some corals.

Gorilla Crab seems to be a pretty large catch-all name for crabs... I've seen people call the brown with black tipped claws that as well as the purple SUPER FUZZY crabs with brown claws (like this one). From what I can hear they can only cause issues for small sleeping fish if the crabs get to a certain size, right? If so, that size range is what I'm trying to figure out.

 

[Flippers4pups]

Without a picture, yes calling it a gorilla may not be spot on. Most of the time crabs with pointed claws are not reef safe.

 

[Luananeko]

The one I spotted in my display tank seems to be the same as the one I had IDed in this thread: https://www.reef2reef.com/threads/another-hairy-crab-id.519623/#post-5443559

It was IDed as Spineback Hairy Crab, Pilumnus Sayi by the Wet Web Media folks. The TBS folks called it a Gorilla Crab as well though when I sent them a picture. Yay for common names being confusing ?

Edit: Also, I have verified this is NOT the same crab as the one I photographed in my refugium, as "Mr. Fuzzy" has been spotted still cruising around up there when I spotted his twin down in the display tank. Both crabs seem to have maxed out at the half inch wide carapace.

 

[botheboss]

I’d get them out. I’ve had a 1” crab catch and eat a 3” foxface at night while asleep in the rocks. The bigger they get the more dangerous they become. I’d get a nice big shrimp from the grocery store and build some kinda trap. Them crabs will be all over it trust me.

 

[Luananeko]

I’d get them out. I’ve had a 1” crab catch and eat a 3” foxface at night while asleep in the rocks. The bigger they get the more dangerous they become. I’d get a nice big shrimp from the grocery store and build some kinda trap. Them crabs will be all over it trust me.

Yikes, alrighty then. I guess they're braver at taking things on than I thought. Good to know! I guess I'll keep attempting to trap them

 

[Saveafish]

Gorilla Crab seems to be a pretty large catch-all name for crabs... I've seen people call the brown with black tipped claws that as well as the purple SUPER FUZZY crabs with brown claws (like this one). From what I can hear they can only cause issues for small sleeping fish if the crabs get to a certain size, right? If so, that size range is what I'm trying to figure out.

Captain Jerry from reeferrock.com ( long gone I think ) said Gorilla crabs can be best identified as they will bore in the rock. Hence the name. There are a few other hairy crabs that is very hard to distinguish.

 

[Luna]

Is this a gorilla crab

It hitchhiked with my rock even after curing them without a heater for about a month. I noticed it in my tank a year after it was set up. I think it’s still in there 4 years later cause the other day I notice a molted crab body.

 

[Saveafish]

Rounded punchers, I'm thinking a type of fuzzy matrix. Or teddy bear crab. Gorilla crabs Get big. After 4 yrs its be snow crab size or soft shell crab size. It be big enough to boil.

 

[Luananeko]

Captain Jerry from reeferrock.com ( long gone I think ) said Gorilla crabs can be best identified as they will bore in the rock. Hence the name. There are a few other hairy crabs that is very hard to distinguish.

From what I've seen, these guys appear to be sand diggers. I've seen the one in my refugium digging huge holes under the rocks. Definitely still predatory though, as I nearly caught the one in the display tank while it was hunting one of my biggest hermit crabs tonight on top of the rocks. He managed to twist out of my forceps and dive back into the rocks though. Arg!

I tried baiting a shot glass half buried in the sand with a piece of silversides.... I've emptied it 3 times tonight so far of hermit crabs, but my target dude still hasn't taken the bait. One of my pistol shrimps even fell in at one point, but swam up and out just fine.

 

[chris85]

Try a peice of window screen with bait in a pantyhose zip tied to the screen.
How big is your tank

 

[Luananeko]

Try a peice of window screen with bait in a pantyhose zip tied to the screen.
How big is your tank

It's a 65g display with 100ish pounds of live rock.

 

[chris85]

Just get a couple feet of screen and fold it a couple times with the bait in the middle so they have to crawl in the screen then just lift it out. There is a video on youtube i will try and find it when i get a chance.