"Coral crab" sounds like one animal, but people use the name for very different crabs. Search for it online and you will find stories of tiny crabs that live inside coral branches and fight off coral-eating starfish. Those crabs are real, but they live in the Pacific and Indian Oceans, not here. On a Caribbean reef, the crab divers and field guides call the coral crab is a much bigger, bolder animal: the batwing coral crab, Carpilius corallinus.

It is one of the most striking crabs you can meet in Punta Cana: a smooth, heavy, brick-red shell decorated with scarlet blotches and wavy lines of pale dots. It spends the day wedged deep in the reef and comes out at night to hunt. Seeing one well takes a bit of luck and a good look into the right crevice.

Quick Facts

Name: batwing coral crab, Carpilius corallinus; also called red coral crab or queen crab
Size: shell usually 7.5–12 cm (3–5 in) wide; the largest reach about 15 cm (6 in)
Diet: mollusks and other crustaceans
Activity: nocturnal; hides deep in crevices by day
Depth: shallow reefs and rubble, mostly from 1 to about 20 m (3 to 65 ft)
Range: western Atlantic, from Florida and the Gulf of Mexico through the Antilles to Venezuela and Brazil

How to Recognize a Coral Crab

The batwing coral crab is built like a stone. The carapace is broad, rounded and smooth, without the row of spines or teeth along the edge that most reef crabs have; the only teeth are a blunt one at each rear corner. The claws are heavy and powerful, with darker tips on the fingers.

Color does the rest. The base is pale to brick red, covered with scarlet spots and winding lines of small white or yellowish dots. Under a dive light it glows, which is why it is a favorite subject for anyone carrying a torch.

The main look-alike on our reefs is the channel clinging crab or Caribbean king crab (Maguimithrax spinosissimus), the largest true crab in the western Atlantic. It is also reddish and also hides in holes, but its shell and long legs are covered in spines and bumps. Smooth and rounded means coral crab; spiky and leggy means clinging crab. Smaller red xanthid crabs under rubble can confuse beginners, but none has the size and polished look of a batwing.

Behavior: A Night Shift Shell-Crusher

By day, a coral crab tucks itself into the back of a crevice or under a coral head, often so deep that all you see is a patch of red or the tip of a claw. After dark it leaves the shelter to forage across the reef and rubble, using those heavy claws to deal with snails, clams and other crustaceans.

Like other true crabs it grows by molting, and females carry their eggs under the abdomen until they hatch into larvae that drift in the plankton before settling on a reef.

What about "guardian" crabs?

The older version of this page described coral crabs that defend corals from crown-of-thorns starfish. That behavior is real and well studied, but it belongs to tiny guard crabs (Trapezia) living in Pocillopora corals in the Indo-Pacific, as the Florida Museum explains. Neither those crabs nor the crown-of-thorns starfish occur in the Caribbean.

The Caribbean has its own coral-loving crabs, though. The elkhorn coral crab (Domecia acanthophora), only about 2.5 cm (1 in) across, lives in small pits on the branches of elkhorn coral and a few other corals. And the channel clinging crab turns out to be a serious seaweed grazer: in experiments in the Florida Keys, adding these crabs to patch reefs cut seaweed cover by 50 to 80 percent and led to several times more young corals settling. Researchers see them as partial stand-ins for the grazing that was lost when the long-spined sea urchin died off.

Where to See Coral Crabs in Punta Cana

Batwing coral crabs live on our local reefs, but daytime sightings are occasional rather than common, because they stay so well hidden. The best odds are on sites full of holes and ledges. Cuevitas, at about 10 m (33 ft), with its small caves and swim-throughs, and Rock City, with its canyons and crevices, are good places to shine a light into the cracks. Park Reef's coral heads are worth checking too.

The channel clinging crab is often given away by a spiny leg or two sticking out of a hole. For the elkhorn coral crab you need elkhorn coral, and a careful look into the small pits on its flat branches without touching anything.

Our guides know the usual hiding spots, and you can find the coral crab on our species guide. The same crevices often hold an arrow crab near the entrance.

Tips for Divers 🔦

Bring a small dive light. Most of what you are looking for is in shade, even at midday.
Never reach into a hole. A coral crab's claws pinch hard, and the same crevice may hold a moray eel.
Keep your fins and hands off the reef. Elkhorn coral, home of the elkhorn coral crab, is one of the most threatened corals in the Caribbean.
Shine the light briefly and from a distance. These are night animals; a long, bright beam just pushes them deeper.
Look for clues. Broken snail shells near a crevice entrance can mean a shell-crusher lives inside.

Frequently Asked Questions

Are coral crabs dangerous to divers?

No, as long as you keep your fingers out of their holes. A big batwing coral crab can give a painful pinch if grabbed, but it will always try to hide first.

Do coral crabs protect coral reefs?

The famous coral "bodyguards" are Indo-Pacific guard crabs, not Caribbean ones. In the Caribbean, herbivorous crabs like the channel clinging crab help corals indirectly by grazing down seaweed.