Fiddler Crabs: Characteristics, nutrition, curiosities and more

It is time to learn about the fiddler crabs or calling crabs, a species that is characterized by its chelae, pincers or «tongs» extremely different in size.

UCA

Fiddler crabs are decapod crustaceans belonging to the genus UCA and the  Ocypodidae family. There are more than 90 species of these crabs that as we already mentioned, have asymmetric claws, being the largest of them similar to a violin (at least for the criteria of some people)

Main Characteristics Of the Fiddler Crabs

Fiddler crabs are very small creatures, whose size varies from 2.5 centimeters up to 5 centimeters across.

They have three distinct parts of the body, the head, the thorax and the abdomen. Moreover, the fiddler crabs possess four pairs of legs that serve to move, and two other legs, which we all know as pincers, although their scientific name is chelipedes.

The chelipedes in turn are formed by two fingers, one fixed and the other mobile.

They also have ocular peduncles, where their eyes are located. Between these ocular structures small antennas appear, which the fiddler crabs employ as a tactile organ.

The color of these crustaceans depends largely on the species, and the place they inhabit. You can find fiddler crabs of very vivid colors, ranging from violet to black

In addition, they have the ability to change their color under certain circumstances, such as the transition from day to night, when they are in the presence of predators, in very hot weathers and even by the change of season. Their pincers have an orange brown color, in some cases yellow or whitish.

The male has a large front pincer of striking color, which represents up to half his body weight. Its other pincer is small and serves to dig, just like the two pincers of the female, which are smaller and less attractive.

The males use the biggest pincer for three purposes: to attract the females, to threaten the rest of the crabs or other animals and to fight.

This fact generates a serious dilemma, since to attract the females, the pincer has to be as large as possible but at the same time very light. However, when used as a weapon, they must be large, heavy, protected and accompanied by strong muscles.

According to studies developed by researchers from the University of Gonzaga and the Smithshonian Tropical Research Institute, some species develop more the tactics of using the clamp to attract, while others the tactics of using the clamp as a weapon. The specific characteristics of the habitat where these crabs develop, usually have a determining influence on what type of employment will be given to this limb, and therefore its characteristics in terms of weight and size.

In addition, the evolutionary process of each species of fiddler crab can also influence this aspect.

It is possible that during their lives, the male fiddler crabs lose their hypertrophied pincer, due to the particular use of this limb. In these cases, the smaller clamp begins to grow and the lost clamp develops again, but remains small.

Let´s watch this video to learn more about them

Curiosities

It is common to see female violinist crabs, frequently visiting different burrows where males live. This behavior is even more common during the reproductive stage, and not so much in other times. The sexual behavior of these crustaceans, whose males have a large claw that is absent in females, had always baffled the scientists and led to several hypotheses. Until not long ago, it was thought that this behavior was due to a rigorous selection of their partners, but a new study, published in the journal Royal Science Open Science, reveals that females are not particularly demanding when choosing a male. Actually they seek refuge to escape from predators such as birds or to avoid extreme situations of dehydration or heat.

Customs

Fiddler crabs tend to spend a lot of their time in the sand, where they usually look for food. However, they never get too far from the shore, leaving from their burrows only during low tide. The calling crabs breathe through their gills, which are very similar to those of fish.

Behavior

Fiddler crabs are not usually very friendly animals, and are also characterized by being very territorial. Once they have dug their small cave, they defend it from other male crabs of the same species, allowing only the access of the females.

They come out from their burrows to feed themselves and when they return they move their clamps in communication signal. When they do it between males, it means that they must keep at distance from each other, but when the communication is dealt with a female violinist crab is to indicate that they are well received in the burrow.

Life Expectation

Compared with the life cycle of other animals that usually live for many years, the life of the fiddler crab is relatively short. These crustaceans only live two years when they are in their natural habitats, and at most one year more, if they are in captivity and properly cared for. It may seem a very short time, since we are used to see species of crabs that live up to 70 years, such as the hermit crabs ; but two years is a period of life enough for them, to reproduce and maintain their species. Although for us it seems short, two years is an age when they are no longer young, which means that they age much faster than other species of crabs.

Each animal has something different to know, and a way to learn a little more about them is to develop our curiosity. If you want to know why do crabs walk sideways, do not stay with that intrigue, and visit our blog.

Let´s watch this video to keep learning

Family of Fiddler Crabs

There are more than 90 especies of fiddler crabs, the most important will be named following:

Species Australuca

Sub genres:

Fiddler crab bellator, elegans, hirsutimanus, longidigitum, polita, seismella, signata.

Species Cranuca

Sub genres

UCA inverse.

Species Gelasimus

Uca :Borealis, dampieri, hesperiae, jocelynae, neocultrimana, tetragonons, vocans, vomeris.

 

Species Leptuca

Uca: batuenta, beebei, crenulata, coloradensis, cumulanta, deichmanni, dorotheae, festae, helleri, inaequalis, latimanus, leptodactylus, limicola, music, oerstedi, panacea, panamensis, pugilator, pygmaea, saltitanta, speciosa, spinicarpus, stenodactylus, subcylindrica , tallanica, terpsichores, tomentosa, uruguayensis.

How the Fiddler Crabs Reproduce?

As we already know, the male has a big pincer that helps him to protect himself from other fiddler crabs. In addition, when the males expose for a long time such limb, they catch the attention of the females, which follow them to the hole they previously dig as a burrow. Then, they carry out the mating.

The female fiddler crab carries the sperm of the male in the lower part of her body, where it turns into eggs. It is important to point out, that the female doesn´t  leave the burrow for about a week and a half, which is the right time for the eggs to hatch. Then, they are released into the sea during low tide, to carry out their life cycle. In a first stage, the eggs are mixed with the plankton, and later they become larvae that grow little by little until they take the form of a small crab. Later the waves of the sea return them to the sand, where juvenile crabs dig their holes, and which they only leave when the tide is low, to feed. During their juvenile stage, the fiddler crabs molt their shell several times as they grow. These crustacean mate several times a year, and depending largely on the state of the tide. The female can get to expel hundreds of eggs in only one mating with the male.

Let´s watch how they molt their shells

Alimentation Habits of the Fiddler Crabs

The fiddler crabs use their claws to collect their food from the sand.  Moreover, they are omnivorous, which feed  mainly on live and dead prey of animal origin; but when they stay in domestic aquariums brine shrimp, plankton and fish scales can also be provided to them. The remains of animals and their defecations constitute what is called organic matter. The fact of feeding on them, makes fiddler crabs a fundamental species for their habitats. As we can see every living creature has its reason for being and they are all necessary, for one reason or another. Biodiversity is indispensable for our planet, even those species that we can consider dangerous. Recall that human beings have also been dangerous to many species of plants and animals, sometimes extinguishing them from the earth.

Common Habitats of the Fiddler Crabs

These crabs inhabit in mangroves, marshes, and on the sand or mud beaches of West Africa, the Western Atlantic, the Eastern Pacific and the Indo-Pacific. The Fiddler crabs are usually gregarious, and gather in silt banks at low tide. Each individual digs a tunnel of about 30 cm in the sand or mud, which serves as a hiding place and shelter, where they refugee at high tide.  (See our article Mangrove Crabs for further information about other species of crabs that inhabit in such locations)

Fiddler Crabs in Domestic Aquariums

The fiddler crabs are crustacean suitable for domestic aquariums. Many people enjoy having them in such places, so if you are one of them, you should follow the following advices. You must recreate in your aquarium, an environment similar to their natural habitat of coast or beach.

*To avoid fiddler crabs fleeing the house made by you, you have to observe very well if it has a grid, since they tend to climb them, and so proceed to escape

* Another aspect that should be taken into account,  is that the place where the aquarium is located should be a site with an ambient temperature between 20 º C and 25ºC but not exposed to the sun. Fiddler crabs die when they spend a lot of time exposed to it.

*Make sure the aquarium is not exposed to radiators, heating appliances or areas of your house where there are drafts.

*They need a large aquarium of about 300 liters, in which bottom must be sandy, since fiddler crabs have the habit of digging in the sand to hide and protect themselves.

* Decorate it with many bushes, with logs, stones, algae, but a good idea is to do it with plants that are not real, that is, plastics, since they can easily eat or damage the real ones.

*Start by placing most of the sand on one side of the aquarium until it reaches the level you want.

* In order to clean the aquarium, fiddler crabs must be removed from it, and then put in a plastic container with clean water.

* If you have more than two fiddler crabs, and they cannot be together because they tend to fight, the best thing you can do is separate them, to prevent them from getting hurt. If you buy each one separately, and you have no idea how they behave, you should place them with care, and once you see their behavior, you will decide if they should stay in separate aquariums or not.

* In order to properly feed the fiddler crabs, you must place plankton or fish scales in the aquarium. If you notice that after several days their food is still there, the best thing you can do is to change it and add new one. You can also put blood worms and some seaweed.

*Be careful not to overfeed them because this can make the aquarium smell bad like ammonia and make the water cloudy.

* Keep in mind that it is normal for fiddler crabs to eat rotting food.

* To keep your new home cleaner, you should change the water on a weekly basis.

*The brackish water without chlorine and fresh, is key to take care of the health of your crabs. If you see that the aquarium water is evaporating, add a little water. If you notice an ammonia smell or see cloudy water, change the sand and water in the aquarium.

*Remember to add water without chlorine and brackish water. Never use table salt to prepare brackish water.

* Don´t try to help your little pet when he is molting his shell, since they could get scared and die. Neither should the old one be removed from the aquarium, since the crabs eat it, to recover energy after the molting. The shells of these crustaceans contain large amounts of nutrients.

*To prevent these beautiful crustaceans from dying or getting sick, all the advices that have been mentioned must be taken into account, especially regarding the cleaning of the aquarium.

Now that you know all about the care of fiddler crabs, you have to commit to take care of them. Do not use them only as adornment, since they require a lot of care.

Difference between the Female and the Male Fiddler Crabs

We have mentioned throughout the article, the characteristics that the male violinist crab has. It could be recalled that it has a claw considerably larger than the other, that helps it to defend the female and also to dig the small caves or shelters in which they live, when the tide becomes a bit aggressive.

We also mentioned that the female is not very demanding, when choosing who will be their partner. It is enough for them to be protected against any risk.

But to distinguish better all the differences, we recommend you to observe the image very well.

On the left side we see a male fiddler crab, with his two different pincers.

Now on the right side we have a female fiddler crab which has a little difference in the size of her two claws, but it is not as exaggerated as in the case of the male. It can also be observed that it has eight legs, and a shell that protects her.

This means, that in order to differentiate a male fiddler crab from a female, you just have to see their pincers, since the male, has one notoriously larger than the other. The female, although it has a larger one, it doesn´t have the same proportion than the ones of the males.

Learning more about them

Now that you know more accurately, what differentiates a male violinist crab from the female; you should have an adventure, and move to where they live.In this way you can apply what you have learned in this article, and you will also enjoy nature and you will create a stronger bond with them.

You can have fun differentiating them, and observing how the males invite the females to their burrow with their claws, or how they tend to mark their territory with others.

Remember that we learn not only by reading and informing ourselves, but also by experimenting, in order to have our own point of view of this species. So don´t  be left alone with an apprenticeship, it is good that you dig a little more.

Would you like to come here to learn about them

Other Considerations

* As we already know everything about the life of the fiddler crab, it is good to remember, that if you have one in captivity, you should not be alarmed when they molt their shells, and that when they do, you should not remove it from your aquarium , since it is usually their food.

* If for any reason, you get to see one that doesn´t have a pincer, don’t worry, remember that it grows again, and that it is not a topic that you should worry about a lot.

* Remember that they are not very friendly, and if your desire is to have several fiddler crabs in a single aquarium, don´t put them all together without first testing if they get along; otherwise it is preferable that you have them separately.

Important

Did you know that the males fiddler crabs fight among themselves to attract the attention females. So, if for any reason you see them  moving their pincers constantly, and it seems that they have an argument, but then you realize that there is a female nearby, it is because somehow or other, they just want to call the attention of the female.They do it so that she can see that with them she will be really protected.

It may seem a very funny behavior for us, but if we see it from another point of view, many men usually do the same, in order to capture the attention of women, so the behavior of some animals, is not so far from ours .

The only difference is that in the case of the female fiddler crabs, they only do it for protection, to ward off bad things that could threaten them. Women may be a bit similar, but they choose a little more, and many do not seek only protection, but affection…

Finally Let´s learn how to to hunt them