Our World: ‘It’s a rough life’ for a fiddler crab

Fiddler Crab on Tigertail Beach, Marco Island, Florida. Greg Kahn/Staff

Photo by GREG KAHN // Buy this photo

Fiddler Crab on Tigertail Beach, Marco Island, Florida. Greg Kahn/Staff

Size does matter — at least in the case of the fiddler crab.

The sand fiddler crab, scientifically known as Uca pugilator, populates many of the beaches around Southwest Florida. Named for the males having one claw greatly bigger than the other, which is held across their body like a fiddle, the crabs number in the thousands on Tigertail Beach on Marco Island.

The fiddler crabs make their way from their burrows in the early morning as the sun is just starting to peek over the mangroves. The fiddler crabs are cautious at first. They inch their way out, pausing to make sure the coast is clear. The crossing shadow of an osprey will cause them to instantly scurry back into their homes. Other predators include herons, egrets and sometimes raccoons. “They’re pretty vulnerable, they’re always on the lookout,” said Gary Pettit, a marine biologist specializing in carsonology. “They’re pretty well sought after, a delicacy to other animals.”

It’s a life lived constantly worrying about what’s coming up over the horizon. Even passing beachgoers will send the small crustaceans running for shelter, although many of the visitors don’t see the crabs because the top of their shell matches the tone of the sand.

Early morning tasks for the crabs include removing debris from their homes, and feasting on the nutrients found in the sand. As the crabs move back and forth from their burrow, they pick and poke at the sand, shoveling bits into their mouth, where they are able to separate different bacteria and fungus from the sand particles to eat. “They’re basically scavengers,” said Pettit.

The end product is dumped in little piles not far from the fiddler crab’s home.

After the morning feast, the male crabs will stand outside of their home and in a robotic way, raise their large claw into the air, and back down again.

The activity looks as though the crab is trying to leap into the air, but their feet are firmly planted in the sand. They repeat this motion for periods throughout the day. The male crabs do this to attract females. And the larger the claw on the male, the more likely he is to meet a female companion. Female crabs, who do not have one enlarged claw, will walk the sand passing hundreds of males throwing their claws in the air. If they find one they accept, they will march into the burrow, with the male following closely behind, and the two will mate.

The larger claws on the males also help them fend off others from stealing their burrows. “Fiddler crabs are extremely territorial, they segregate themselves by their species and how long they can stand being out of the water,” Pettit said. The crabs seem to play a giant game of musical chairs, with the larger males winning every battle. As a beachgoer approaches and the crabs rush to hide, some are caught too far from their home, so they will battle for a spot in the closest burrow. The larger fiddler crab almost always wins, sending the smaller crab to find either a vacant hole or kick an even smaller crab from its home.

After the danger has passed, the fiddler crabs slowly emerge again.

“It’s a rough life,” Pettit said.

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Connect with Greg Kahn at www.naplesnews.com/staff/greg_kahn

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