Arrow Crab (Stenorhynchus Seticornis): Ultimate Care Guide

Common NameArrow Crab / Yellow Line Arrow Crabs
Scientific NameStenorhynchus Seticornis
OriginOcean / Coral Reefs
Temperature72F – 78F
Water pH8.1 to 8.4
Size2.5 inches

Arrow Crab Facts

  • Arrow Crabs are nocturnal and this means that they sleep during the day and are most active at night.
  • Arrow Crabs can grow up to 2.5 inches, but that is only the measurement of their bodies. Their legs can be up to 3 times that length.
  • Arrow Crabs regularly shed their outer shells in a process called molting. After they have shed their old shell it is important to not remove it from the tank so that they can eat it. They do this to absorb nutrients that they may have lost in the molting process.

Arrow Crab Care

Arrow Crabs (Stenorhynchus Seticornis) are amazing creatures with small, triangle shaped bodies. The head of the Arrow Crab is very pointy, and has a rostrum at the end. A rostrum is a beak-like projection that is essentially a snout. The rostrum of the Arrow Crab is rather long, and serrated looking. On either side of the rostrum are the small eyes of the Arrow Crab. Arrow Crabs may appear odd at first glance, but their interesting shape allows them to easily slip their bodies into crevices, and live among the anemones. In the wild, Arrow Crabs can be found gathered around anemones for protection.

Arrow Crabs are equipped with 5 pairs of long, skinny, spider-like legs. Two of these legs are tipped with claws. The Arrow Crab uses its claws to eat, grab things, and defend itself. Their long claws are adept at getting into hard to reach places to capture their food.

Their bodies only reach up to 2.5 inches in length at full maturity, but their legs can be up to 3 times longer. Each Arrow Crab leg is tipped in a deep violet.

Arrow Crab (Stenorhynchus Seticornis)
Arrow Crab (Stenorhynchus Seticornis)

Do Arrow Crabs Shed?

Like all crustaceans, Arrow Crabs have to shed their exoskeletons to grow. They do this in a process called molting. They will shed their old shell and then eat it. The molting process is amazing. It can even help Arrow Crabs regrow their lost limbs. When observed, you can see the Arrow Crab regrow its lost limb a little at a time with each molt. The entire molting process can take a few hours for the Arrow Crab to complete, and during this time they are vulnerable to predators. Arrow Crabs are prone to stress during this time as well, and need shelters like caves so that they can feel secluded and safe.

Food and Diet

Arrow Crabs are scavengers and opportunistic feeders in the wild.They are most active at night, and can often be found climbing around anemone or rocks in search of food.

As Arrow Crabs search for food, they use their long claws to get into crevices and extract their prey. In captivity, they will readily accept any foods that you offer them. In the wild, Arrow Crabs will eat algae, worms, invertebrates and dead organisms.

What do Arrow Crab Eat?

Arrow Crab will eat almost anything that they can get ahold of. They are scavenging, opportunistic feeders that emerge at night to look for food. They can be found feasting on dead organisms, algae, invertebrates, and worms. In captivity, you can expect Arrow Crab to readily accept flaked, frozen, or live foods. They are a great clean up crew for a tank as they will eat detritus that falls to the bottom of the tank. Even though they are great helpers in keeping their aquarium clean of debris, this should not be relied on to keep the tank clean. Arrow Crabs are sensitive to changes in their water parameters and can quickly become ill if problems persist without correction.

Do Arrow Crab eat Bristle Worm?

If given the opportunity, Arrow Crab will eat and go after Bristle Worms. Bristle Worms are a tasty snack for a hungry Arrow Crab. Bristle Worms are hitchhikers that often arrive in a home aquarium unknowingly from the addition of live rock, and in most cases they are considered a pest. Nocturnal, and experts at hiding, Bristle Worms can hide in tanks for months until they are discovered. A tank that houses Arrow Crabs will not have to worry about Bristle Worm infestations. Arrow Crabs are experts at seeking them out, and once the Bristle Worm is caught, the Arrow Crab will use its claws to grab ahold of the Bristle Worm and pull it apart so that it can be eaten safely by the Arrow Crab.

Do Arrow Crabs eat Flatworms?

Arrow Crabs will eat Flatworms if given the chance as they are an opportunistic feeder. Flatworms are not healthy for a reef tank as they can overcrowd the coral and block out the light. Flatworms are not typically wanted in the home aquarium and are often treated as pests to be rid of. Arrow Crabs can help keep these unwanted pests from damaging your coral quite efficiently. Arrow Crabs use their long, skinny claws to grab ahold of flatworms so they can be extracted from wherever they are hiding, and be eaten.

Arrow Crab Size & Lifespan

Arrow Crabs can reach up to 2.5 inches at full maturity, but their legs are not counted in this measurement, and they can be up to 3 times their body length. If cared for properly, you can expect your Arrow Crabs to live up to 5 years. This is roughly the same lifespan as they reach in the wild. It is vital to the health and happiness of Arrow Crab that they are kept in the correct conditions, and their water kept clean of nitrates and ammonias. Build up of fish waste or incorrect water parameters can quickly cause Arrow Crabs to become ill.

Arrow Crab Tank Requirements

Arrow Crabs require at least a 30 gallon tank or more. They are a territorial species, and if they are in a tank that is too small they can not establish their territory.

Arrow Crabs are very sensitive to nitrates and ammonia in the water, and they have to be acclimated to their new environment very carefully. Arrow Crabs need a water temperature that ranges from 72F to 78F, and 8.1 to 8.4 pH. They will require a reliable heater to keep them at this warmer temperature all of the time. The use of a standard marine salt blend will help provide the Arrow Crab with Iodine and Calcium. These are essential to the Arrow Crab for shell maintenance and help aid the Arrow Crab in the molting process.

Arrow Crab Tank Setup

When setting up an aquarium for Arrow Crabs, you will want to go with a setup that closely mimics their natural environment. Soft, sandy substrate, and living rocks are a good choice for an Arrow Crab aquarium. Caves set up out of rock give Arrow Crabs a stress-free place to hide. It also provides them with protection from predators when they shed their exoskeleton and are most vulnerable. 

Are Arrow Crab Reef Safe?

Arrow Crabs are not reef safe as they have been known to eat polyps, and soft coral. If you are introducing Arrow Crabs into a reef setup it is advised that you do so with caution. Arrow Crabs are great for ridding the tank of parasites that will harm corals, so they could be a helpful addition. With any introduction of new species into community setups, you will want to monitor the tank.

Arrow Crab Breeding

When Arrow Crabs are ready to spawn, the male will pin the female down so that he can deposit his sperm packet into the female crab. The female Arrow Crab will then carry those eggs until they are ready to hatch.

Offspring that have just hatched are called zoea. Zoea is the larval stage of the Arrow Crab’s growth. These zoea live in open water feeding on plankton until they are able to molt. Eventually the zoea will molt enough to become a new form called a megalop. During their megalopaedic stage of development, the Arrow Crab juveniles are starting to look more like an actual crab as their limbs are really starting to form. Arrow Crab juveniles will then molt repeatedly until they are in their mature form.

How Do You Tell the Difference Between a Male and Female Arrow Crab?

Fortunately, it is rather easy to tell the difference between male and female Arrow Crabs just by observing them when they have reached adulthood. Fully mature Arrow Crab males have more triangular shaped bodies whereas the females have more rounded body shapes. The males also tend to have larger claws than the females do.

Arrow Crab Disease

It is uncommon for Arrow Crabs to get sick, but if there are problems with their water quality there can be problems with the crabs. It is important to make sure that you are monitoring their water parameters frequently so that you are aware of any changes and can correct them. Stress is a huge factor in the longevity of any crab. A stressed crab will get sick quickly, and potentially never recover.

Arrow Crab Tank Mates

 It can be tough to find a tank mate for Arrow Crabs that are large enough to be safe around Arrow Crabs, but not large enough that they see the Arrow Crabs as food. Arrow Crabs are opportunistic feeders, and this makes it tough to find compatible tank mates for them. Other invertebrates that have heavy defenses such as other species of crab will make for good tank mates for Arrow Crabs.

Arrow Crabs are incompatible with more tank mates than they are compatible with. This makes it tough to decide which tank mates to choose. Whichever you choose, make sure that you are monitoring the behavior of your Arrow Crabs with others.

Are Arrow Crab Aggressive?

Arrow Crabs are very territorial. They do not do well with other Arrow Crabs unless certain conditions are met. If you are planning on housing more than one Arrow Crab together, you will want to make sure that you have an aquarium large enough for each crab to claim it’s own territory.

Arrow Crab and Clownfish

Arrow Crabs and Clownfish both enjoy roughly the same water parameters, but Clownfish are small enough that Arrow Crabs could consider them a meal. It is said that the two can safely be housed together provided that all their needs are being met. Owners of some Arrow Crabs suggest that even well-fed Arrow Crabs will go after fish in their aquarium.

Arrow Crab and Cleaner Shrimp

Arrow Crabs and Cleaner Shrimp both enjoy the same water parameters and dietary structure, but if you are wanting to pair the two together in a community setup you will want to use caution. It is possible that the territorial Arrow Crab will see the Cleaner Shrimp as food and go after them. If you notice that your Cleaner Shrimp are missing limbs or antennae, you will know that they two can not be housed together. You do not want your Cleaner Shrimp to experience this if you can help it, so be sure to check on your tank often.

Arrow Crab and Emerald Crab

Emerald Crabs and Arrow Crabs both enjoy roughly the same water parameters and diets. However, Arrow Crabs are an aggressive, territorial species of crab. It is not advised that you try to house them with other crabs. The two species of crab will most likely spend their time fighting one another.

Where Can I Find Arrow Crab for Sale?

If you are looking to purchase an Arrow Crab for your aquarium, you can to find them for sale at some specialty pet stores or online. You will want to make sure that you are purchasing them from a reputable source to ensure that you are getting a healthy Crab. You can expect to pay around $15 for one Arrow Crab.