The Sally Lightfoot Crab: A Real Character of a Crustacean

P. gibbesi is a interesting, vertically-flattened crab commonly sold in local fish stores.

P. gibbesi is a interesting, vertically-flattened crab commonly sold in local fish stores.

Sharing the surname of a famous Canadian folk singer, of whom I’ve been an ardent fan for many, many years (once again confirming that my profound nerdiness knows no bounds), the Sally Lightfoot crab, a.k.a. the nimble spray crab, of the Tropical West Atlantic, Caribbean, and Indo-Pacific, is a common offering at local fish stores specializing in marine livestock. This crab can make for an interesting aquarium resident, provided its true nature is understood and tankmates are chosen with care.

Physical traits

The Sally Lightfoot crab (Percnon gibbesi)—not to be confused with Grapsus grapsus, a common semi-terrestrial crab species found along the Pacific coast of the Americas and on the Galapagos Islands that shares this same common name—is a small (reaching approximately 4 inches in diameter, from leg tip to leg tip), vertically flattened crab with brown to olive-brown overall coloration and tan to yellow or orange bands on its legs. Among the Sally Lightfoot’s more endearing traits are the tiny antennae located above its eyes, which continually flick up and down to the amusement of onlookers.

Behavior

P. gibbesi is a startlingly fast-moving crab that scurries about the rockwork and substrate, stopping to pluck anything edible with its front claws, which seem to be in perpetual motion. One could argue that its body shape and movements might be a bit too reminiscent of a fast-moving spider for the comfort of arachnophobic aquarium hobbyists.

This species is commonly sold as a harmless herbivore/scavenger. When specimens are young, that’s generally true enough. Smaller specimens will content themselves with plucking algae and uneaten food from on and between rocks (a job made easy by the crab’s flattened body), largely ignoring any tankmates that pose no threat to them.

However, before bringing that cute Sally Lightfoot home and adding it to your system, it’s important to be aware that this harmless, “herbivorous” crustacean isn’t always so well behaved in aquariums once it matures. At that point, this species tends to become more aggressive and predatory. It will even grab small fishes and other invertebrates if it’s able.

Feeding in captivity

In addition to food items they graze or scavenge/capture for themselves, Sally’s will accept just about any standard fare you can offer to fish, so feeding them in aquaria is pretty much no challenge whatsoever. Offer a variety of meaty and algae-based foods. Keeping them intentionally well fed may help to reduce the predatory tendencies of mature specimens as well—but there are no guarantees.

Tankmates

Because P. gibbesi can’t be trusted in the long term around small fishes, crustaceans (including others of its own species), and other invertebrates, tankmates must be chosen carefully. Any fish sharing the tank must be large enough to avoid getting grabbed by the Sally and must not include crustaceans on their own natural menu. Mature Sally Lightfoots aren’t reliably trustworthy around sessile invertebrates either, so I would discourage including one in a reef system. Besides, with this crab’s flattened body and lightning quickness, it could prove to be pretty tough to capture and remove a troublemaking specimen from an established reef system.

Photo Credit: tato grasso

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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.

Comments

  1. Paul Baldassano says:

    Sally Lightfoot crabs are very common in the Caribbean and are found everywhere there. One problem with them is that they are intertidal animals and usually eat algae just at the water’s edge or fairly high out of it. That behavour is what prevents me from keeping them any longer as my coral and rocks extend above the water allowing the crabs to climb out of my tank and walk across the room to die under the couch. I have had quite a few of them, and that’s where they all ended up.

    • Jeff Kurtz says:

      Thanks for this cautionary tale, Paul. I’m sure fellow salties will take heed.

      There’s also another piece of advice I should give regarding this species that I forgot to include in my post: If anyone out there ever gets the bright idea to place a molted Sally Lightfoot exoskeleton on a soda can in the refrigerator in order to frighten their significant other, resist that impulse! You will suffer mightily! Don’t ask me how I know this.

    • Lol !! I remember a long long long time ago I had this Clibanarius Vittatus who was such an acrobat it could climb up the air tubes…. Pull itself out of the tank… and jump to the floor where I usually found it dried up on the living room carpet… The same with Moray Eels that are so powerful: they can lift plate glass if it’s not weighed down by cinder blocks or fixed on a heavy duty glued on frame…
      An old distributor friend of mine often saw Octopus clinging to the wall above the cash register when opening shop in the morning !!!
      Remember… It’s our responsibility as Aquarists to act responsibly….

      • Jeff Kurtz says:

        He he! I’m envisioning that octopus clinging to the wall. Talk about a source of alarm for arachnophobes!

  2. I love my little Percnon Gibbesi! She is absolutely adorable!

  3. How long can SLF’s live out of water? MY SLF escaped yesterday, and I can’t find him anywhere. :'(

    • Jeff Kurtz says:

      Hmm, I don’t know exactly how long they can survive out of water, but, as Paul B indicates above, it’s not especially long. I’m wondering, though, whether your specimen actually escaped or is just staying out of sight while it molts and its new exoskeleton hardens off. Do you have rockwork extending right up to the top of the tank that might facilitate an escape?

      • I’m familiar with the molting etc. He definitely escaped. I emptied the tank looking for him. He climbed up a pipe, and squeezed through the lid.He pushed the rag out of small hole that’s in the lid for the pipe. I used it to block him just in case. I knew he was smart, but did not expect him to push it out. I’ve had him since he was the size of a pencil eraser. He molted every three weeks.

        I keep hoping he will show up. I’m shattered. He is so awesome and we interacted with one another every day.

        • Jeff Kurtz says:

          Sorry to hear that, Kelly! I know how easy it is to get attached to our salty pets. I hope he shows up for you!

          • Thank you Jeff.

          • Kelly Peissner says:

            Jeff, It turns out my crab was a marble rock crab; not a SLF like I was told. No wonder he was so ornery and ate any living creature I put into the tank. He was so cute. I loved the little devil. Still do. I hope another one shows up in one of my tanks one day.

  4. Maybe while he is interacting, he will text you about his whereabouts

  5. I love my Sally however even though doing some light research before deciding to add the crab I soon found out the costly behavior of my Sally. I have lost feather duster,sea stars,damsels,shrimp,red and blue leg crabs,and a few others. Sally is now resting in its own nano time out. Wish I would have read more articles like this one rather then the not so clear ones I did read.

  6. Awesome. I do the same. I got another SLF the other day. It’s a female. She is trying to molt right now so is very unsocial.

  7. Anyone know of any smaller fish that can live with a sally in a Nano tank?

    • Kelly Peissner says:

      I have several Gobies and a wrasse living with mine along with peppermint shrimp and a skunk cleaner. I think it depends on the personality of your SLF. Mine seems to like her tank mates so far, and I feed her meaty food every night. ~tap on wood~

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