The aggressive arrow crab. 

A Long-limbed Aggressor

Known for their incredibly long, thin legs, the arrow crab, scientifically known as Stenorhynchus seticornis, actually gets its name from its triangular body, which is shaped like an arrowhead. While they’re nicknamed spider crabs because of their long limbs, these crabs are also known for being aggressive in their natural habitats. Arrow crabs, especially males, can be quite territorial.

In the Wild

Found in the coral reefs of the Caribbean, these fascinating crabs can also be found in the coral reefs along Mexico, Florida, and Texas. Primarily nocturnal, arrow crabs will do most of their feeding at night. Though they are mostly scavengers, they have been known to prey on small worms and tiny sea creatures.

In the wild, these crabs can grow up to 10 inches, but female crabs tend to be much smaller.

In the Tank

Because arrow crabs are scavengers, they make good additions to reef tanks that are over 20 gallons because they can help clean. For many reef habitats, they can make good tank mates, but as they are aggressive, it’s best to keep these crabs alone or with fish that are too large to become prey. Large species of shrimp, including peppermint shrimp or camel shrimp, can also be suitable.

Arrow crabs also need sufficient food or else they will pick at coral polyps, shrimp, or slow moving fish. Giving arrow crabs zooplankton, seaweed, or brine shrimp usually keeps them happy.

In aquariums, arrow crabs are easy to care for. They do require water temperatures of around 72-78 degrees Fahrenheit with a pH of around 8, which is typical for many reef tanks. They should also have plenty of hiding places in natural coral or living rocks, especially since they will need somewhere to hide while they sleep during the day. 

Pest Control

Not only do arrow crabs help keep tanks and reefs clean, but they can also take care of some pests. Bristle worms are a species of segmented oceanic worm that can grow up to 24 inches long. They can be irritating to certain reef fish and sea creatures, and they multiply quickly, which means you could have an infestation on your hands. However, the arrow crab’s aggressive nature can help rid your tank of these worms.

Though they can be quite aggressive, arrow crabs are most known for their long limbs and their body shape. As they can control pests, they can be an interesting and beneficial addition to reef tanks.

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