By 2019-08-29 InNature

Fiddler crabs

Whilst returning to the car after an amazing morning photographing greater flamingos at sunrise (available on my website), I overheard another visitor to Ludo saying “oh look at that poor crab, it is missing a claw”, which soon then went on … “Wait! Lots of them are missing a claw!”

Fear not, these are male fiddler crabs and this is normal. In actual fact, they have both claws but one of them, called the major claw, is considerably larger than the other. Female fiddler crabs have two equally small claws. There are more than 100 different species found around the world, the ones we see in the Algarve are the only species found in Europe which has the scientific name of Uca tangeri.

The sandy, muddy base of the Ria Formosa is the perfect habitat for the fiddler crab and, at low tide, you can spot them almost anywhere in this amazing national park. A great spot to look for them is at Ludo, near the west end of the runway of Faro airport, where during low tide it’s impossible to count the numbers of them. They are everywhere!

Fiddler crabs (also known as calling crabs) take their name from the males’ mating ritual of waving their large major claw, which looks like they are playing a violin. These crabs have a life span of only two years.

Burrows are dug in the ground which have an entrance tunnel before a 45-degree bend passes into a (sometimes long) tunnel into a chamber. Studies have shown that they usually move to new burrows within just one to two weeks.

At low tide, the burrows are exposed and the fiddler crabs will emerge. However, don’t expect to see them between November and March as the surface temperature must be 18ºC before they will emerge. However, during the warmer months, you will not fail to spot them. During the winter season, you may spot the openings of the burrows, but you are unlikely to spot a fiddler crab venturing outside.

The males will fight for real estate rights and it’s amazing to watch them fight with their major claws. It’s like watching professional boxers fighting with one hand behind their backs!

Fiddler crabs forage through sediment for anything edible such as algae and fungus. Once they remove any edible content from the sediment, they can be seen leaving any residual waste in small balls.

It is believed that the larger the claw, the better the chance for a male to attract a mate and courtship to begin. However, the female does not choose her mate simply due to the male showing off his claw. Studies have shown that burrow size relates to the size of the males’ claw and, therefore, the female chooses her partner because of the size of his burrow rather than the size of his claw.

As with all crabs, fiddler crabs shed their shells as they grow and can also re-grow legs and claws. If a male has lost a major claw, a new one will develop on the opposite side during the next shell moult.

By Craig Rogers

Male fiddler crab showing his major claw

Male fiddler crab showing his major claw

Female fiddler crab

Female fiddler crab

Male fiddler crabs in combat

Male fiddler crabs in combat

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