The tanning crab (Uca tangeri) was first described in 1835 by French naturalist Joseph Fortuné Théodore Eydoux. The ship with him on board ran aground near the Algerian city of Tangier, and the naturalist had no choice but to study underwater inhabitants. In memory of this significant event, the crab received its Latin name.
This decapod crustacean belongs to the family Ocypodidae from the suborder Pleocyemata and lives on the eastern coast of the Atlantic Ocean. Due to the fact that its fighting claw can sometimes reach very impressive sizes and weigh more than half the weight of the crab itself, among many African peoples it is considered the product of evil forces and even a great sorcerer, capable of casting spells on an inexperienced diver or fisherman.
The habitat extends to the southern coast of Portugal and Spain, as well as to the coastal waters of Africa from Morocco to Angola.
Large colonies of these crabs are found primarily in mangroves, where they find refuge in intricate labyrinths of roots. They love salt water, but often also settle in river mouths, carefully avoiding sandy, rocky and pebbly areas of the coast.
An important feature for choosing their habitat is the regular tides. Entire crowds of beckoning crabs hunt in accumulations of various waste thrown ashore by the ocean. They often settle directly in the vicinity of coastal cities, hoping to make a good living from the products of human activity.
In Uca tangeri colonies, each individual digs his own burrow and carefully guards it from his relatives. The round entrance opening continues with a narrow cylindrical corridor, which widens at the end, forming a small, cozy living chamber.
The lure crab usually goes out to fish at night, but can show some activity during the day if the weather is not hot and dry. With the onset of low tide, he leaves the shelter and quickly moves sideways along the shallows in search of food supplies.
Its diet consists of rotting algae, small sea creatures and carrion.
The voracious creature filters a huge amount of silt and sand to get to nutrients. Having sent the next portion into his mouth, he mixes it with saliva and carefully grinds it with his jaws, swallowing all the most edible, and removes the rest from the intestines in the form of small lumps.
By the end of the low tide, a whole pile of such lumps grows near his hole. Before the end of the low tide, the hardworking and thrifty crab pulls quite large pieces of carrion into its burrow so that it has something to eat during the high tide.
Alluring crabs have an extremely quarrelsome character. They often fight among themselves, not only males, but also females. Gentlemen, seeing an enemy, strive to sneak up on him from the side and give him a hearty bite with a powerful claw, while ladies prefer to push each other with their shells.
Fighting can last several minutes and often results in serious injury. A male that has lost a claw may remain single during the period of mass marriages. He simply physically will not have anything to lure girlfriends for procreation. However, after the next molt, the claw will appear again, sometimes larger and more beautiful than before.
During the mating season, the carapace of males acquires a brighter color and even shines as if polished. The male changes his usual gait in order to make the right impression on the female.
His movements become more proud and imposing, accompanied by frequent sideways jumps and persistent swings of his large claw. If the male’s dancing talents make a favorable impression on the female, she comes closer to him.
The charming dancer quickly pushes her into his hole before she has time to be disappointed in his charms. An hour later, she leaves the hospitable burrow and eventually lays eggs, which she carries on her abdominal limbs in special capsules. When the development of the embryos approaches the end, she enters the water and leaves the eggs, returning back to the colony.
One female can lay several thousand eggs.
From the laid eggs, free-swimming larvae about 1 mm long, called zoea, appear in the plankton. After multiple molts, they turn into adult crabs and go to look for a place in the nearest colony.
Crabs molt regularly, shedding their old, tight shells. After each moult, the claws increase in size, continuing to grow until sexual maturity.
The large claw grows to 60-65 mm, while the length of the carapace is 33 mm and the width is 47 mm. The surfaces of the claws have a pronounced granular texture. Their upper half is movable and, closing with the lower, acts like tongs.
One of the claws is huge in size and serves as a combat weapon and for pinching off large pieces of food.
The head and chest are covered with a quadrangular carapace with a tuberous surface. There are four pairs of walking legs.
On the sides of the base of the rostrum there are slit-like eye sockets, in which there are compound eyes set at the ends of the stalks.
The lifespan of a lure crab is about 3-4 years. Few live to such an old age, because they have a lot of natural enemies. During low tide, tens of thousands of them are eaten by various birds and animals.
First, let's talk a little about these interesting creatures.
Alluring crabs (family Ocipodidae, Uca sp.) got their name for a reason, as they have a very original claw structure and very original behavior.
Male crabs have one of their claws much larger than the other. This large claw will help scare off the enemy in case of danger, and will lure and attract a crab friend. So the crabs sit near their burrows and wave their claws, like a traffic controller at an intersection.
Also, some types of beckoning crabs are capable of making sounds that are a bit like the chirping of cicadas or grasshoppers. What interesting creatures these are!
Undoubtedly, they are interesting to watch and some lovers of aquarium exotics keep these crabs in their aquariums.
However, for a full and prosperous life, they need to create optimal living conditions in the aquarium. This is not as simple as it seems at first glance.
However, it’s not that difficult, especially after you read the instructions from Sergei Leonov (Mikhailovka, Volgograd region, Russia) on arranging a home for beckoning crabs, which he kindly shared with the Tashkent aquarium website.
To set up a crab farm, several necessary conditions must be met.
This primarily concerns the substrate. It should be light and free-flowing, so we recommend using coral sand for this purpose.
Why coral? Not because I like to show off (which is what it is!), but because everything is determined by the practical side.
So, what prompted me besides the fact that I had a 14-kilogram bag collecting dust in my stash ( photo 1) and the fact that he is amazingly handsome?
It's all about such a banal thing as the importance of maintaining a strictly specified pH value for anyone wearing a shield (read armor!) on their back. It (the bag), or rather its contents, does not allow the pH itself to decrease and will keep it at an acceptable level of about 7.
It is very difficult to maintain this same “PyKhy” at the proper level in such a small container as mine.
The aquarium is only twenty liters, because there are only two crabs living, and I didn’t even intend to keep a colony.
For crabs, bottom area is the most important thing. Therefore, a square jar with a small height was taken ( photo 2).
The size of this aquarium is simply ideal in that it fits like a glove, both in height and width, and fits the shelves of my aquarium cabinets ( photo 3).
So, the coral soil has a slightly grayish color. Therefore, before placing it in the aquarium, we rinse it a little.
We take a small vessel - it is best to have a separate nylon container for aquarium affairs - and very carefully rinse the soil under running water with low pressure of warm water.
If the sand is fine, like mine, 0.5-1 mm, then you need to be doubly careful. It stirs up very easily, and thus, due to an oversight, I was left with almost half of the initial mass.
The sand will foam and turn the water white, but don’t be alarmed, this is normal ( photo 4). That's how it should be!
If this is not the case, then it is either already washed, or... you need to start getting scared. Fill, rinse, drain three or four times until the sand turns boiling white ( photo 5).
After the soil is washed and squeezed out (a little), we evenly cover the bottom surface with this coral sand in a small layer, gradually increasing it towards the wall or corner, like mine ( photo 6).
In addition to the layer under water and protruding parts of land, crabs find it very pleasant to wander around in shallow water. There is nothing complicated about this. We just make a small mound.
In the middle of the bottom of the aquarium we place a structure along which the crabs can get to the surface ( photo 7).
Why in the middle? Yes, simply because they, like “wounded in one place,” are constantly ready to escape and will not fail to take advantage of the edge of the aquarium if they can reach it. If the decoration is in the middle, then there will be only water around.
Thus, we have created all the necessary conditions for keeping alluring crabs, which, I am sure, will delight you with their originality and cheerful disposition.
The crab received the name “alluring” due to its special habit of making alluring movements with its large claw, with which it simultaneously scares away other males and lures the female. At night, or being in dense thickets, in conditions of poor visibility, the male has to not wave his claws, but knock on the ground. Such rather loud sounds and vibrations also attract the female, and she rushes to the call of the male.
It is worth noting that alluring crabs lead an almost land-based lifestyle. These crabs dig their holes on the seashore at high tide, during which they hide in holes, and at low tide they search for food. There are two species of crabs, one of which (Uca tetragonon) lives in the lower part of the shore, which is flooded at high tide. He digs minks among fragments of shells and fragments of dead corals.
And the second species (Uca perplexa) inhabits the upper bank and lives only on muddy soils. At times, representatives of both species go quite far from the coast and end up in damp forest zones with fresh water bodies.
Female California fiddler crabs will often inspect and test over 100 males, even inspecting the male's bachelor pad before choosing a mating partner. During the process of seducing the female, the male fiddler crab stands at the entrance to his hole on the shore and, waving his claw, gives the female a “come here” sign, luring her. Interested females inspect the males and, if they like what they see, partially or completely climb into the male's den to measure him. When the male is chosen, the female enters his house, blocking the entrance to the hole. Having settled down, the couple begins to mate and lay eggs, which will later be washed out of the hole by the waves.
Scientists have long been intrigued by the ability of tiny fiddler crabs to change the color of their shells from bright blue to dull, dirty shades. Until now, the reason for this color change was unknown. But recently, researchers from the Australian National University (ANU) found that crabs change color to avoid being eaten by birds of prey. To do this, scientists studied a specific species of fiddler crab, Uca vomeris, on the northeast coast of Australia. Because some populations of these crabs are characterized by dull colors while others are very colorful, the researchers looked at the color variations of the crabs in three different sites: one group was dull, another was bright, and the third was mixed. It turned out that there were very few birds of prey in the habitat of bright blue crabs compared to the dominance of predators in the habitats of dull crustaceans.
To confirm their guess, scientists created an experimental model and tested whether crabs change the color of their shell when threatened with being eaten. They found two very colorful crabs living close to each other and placed a wooden screen between them. One crab was left alone, while the other felt the intense attention of a bird of prey every few minutes. In reality, the bird was not real - its role was played by a black ball suspended on a fishing line. But crabs have poor eyesight, and the ball was enough for the crustacean to sense the presence of the bird.
Over the course of several days "under the bird's care," the crab changed its color to a dirty shade, while the other remained bright. Scientists suspect that blue color is usually used by crabs to identify their neighbors and avoid unnecessary quarrels with them. The researchers' next step is to find out whether dull coloring has an effect on the "friendship" between crabs.
By the way, fiddler crabs previously surprised scientists with their social skills. In addition, they have been recognized as the most picky and picky creatures on Earth.
Belongs to the class Crustaceans. The lure crab is a highly organized semi-terrestrial crustacean of small size. A special feature of this animal is its giant right claw. While moving, the alluring crab makes certain movements with its large claw, as if luring individuals of the opposite sex to itself and vice versa, scaring away other crustacean animals. That's why the crab got its name. The lure crab also has regenerative abilities. A claw that falls off for some reason grows back. In some cases, the new claw of the beckoning crab grows larger than the previous claw.
The body of the alluring crab, like that of other representatives of this species of crustaceans, consists of a cephalothorax and a reduced abdomen. The whole body consists of segments. The segmented head, consisting of two pairs of small antennae and stalked eyes, is smoothly connected by a segmented abdomen. The head consists of three pairs of jaws and three pairs of jaws. The chest consists of five pairs of walking legs, of which the first pair of legs is claw-shaped. The head and chest of the beckoning crab are covered with carapace. The carapace is the shell that covers the body of the crab. Only males have a huge claw. In females, both the right and left claws have the same structure.
Animal characteristics:
Dimensions: body length without limbs 1.5-2.5 cm, with claws 5-10 cm.
Color: The beckoning crab's body has different colors, mainly dark gray, dark red and black colors. Large claw and limbs: red-yellow-white and other gradually changing colors.
The digestive system of the lure crab consists of three parts: the middle - endodermal section, the anterior section and the posterior rectum. The anterior section consists of the esophagus and stomach. The lure crab feeds mainly on small crustaceans, algae, aquatic plants and detritus; it can also consume large quantities of soil.
Alluring crabs are dioecious animals. The female genital openings are located on the sixth thoracic segment, located near the third pair of walking legs. The male genital openings are located on the eighth thoracic segment, located at the fifth pair of walking legs. In males, the holes are tubes that are filled with germ cells during the breeding season. During mating, the male introduces these cells into the genital openings of the female. The female lure crab mounts the eggs on her abdominal legs and holds them there until hatching.
Alluring crabs are widespread in tropical waters, mainly on the islands of the Pacific and Indian Oceans.
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Basic data:
DIMENSIONS
Length: 3-4 cm.
Claw length: up to 5 cm.
REPRODUCTION
Puberty: from 1-2 years.
Mating season: several times a year (depending on the species, place of residence and tides).
Number of eggs: several hundred.
Incubation: 7-10 days; The eggs hatch into microscopic larvae that swim in the plankton.
LIFESTYLE
Habits: single inhabitant of the littoral zone; lives in burrows.
Food: organic particles.
RELATED SPECIES
There are many species of crabs belonging to the genus. They vary in color and size.
There are many species belonging to the genus of alluring crabs. These small, sedentary inhabitants of warm, muddy coastal waters are distributed throughout the world. The way crabs feed is determined by the ebb and flow of the tides, since these crustaceans cannot feed underwater.
While searching for food, beckoning crabs dig up sand and silt with their claws and front grasping legs, grab food with their jaws and bring it to the mouth. In the mouth, the edible part of the food is sifted out, and the inedible remains are excreted out. Because sand and mud contain few nutrients, crabs must spend a lot of time searching for food. Males spend especially a lot of time feeding. This is due to the fact that they can only use their left claw. The right claw is too large to be convenient for holding food, and during feeding it interferes with the males.
With the beginning of the mating season, males begin to court the female. With their right claw they make special, very interesting movements. Different species of crabs use their large claws differently. First, the male runs back and forth across the sand and waves his right claw in front of the female, and then walks forward, hoping that the female will follow him. Researchers noticed that males, during the mating dance, knock their claws on the ground and stomp their feet, just like locusts do. Mating of crabs takes place in the male's burrow. After mating, the female lays a large number of eggs. The larvae of alluring crabs, having hatched from eggs, travel for a long time by sea as part of plankton, they are carried by the waters of the ebb and flow of the tides. As the larvae grow, they become more and more similar to the adults. 
Adult crabs spend most of their lives in the lower part of the littoral zone. They are found on both silty and sandy soils, in which they tirelessly search for food. On coastal shallows they often form dense settlements, but only one crab lives in each hole. Alluring crabs are sedentary animals; they try not to move away from their holes and, in case of the slightest danger, immediately hide in them. 
Crab larvae, which are carried from place to place as part of plankton by the ebb and flow of the tides, become easy prey for a number of predators. Waterfowl eat them in the thousands, collecting them from the surface of the water. The beckoning crabs that have grown up also have many enemies. They are hunted by martins and frigates. On the coast, crabs are collected by sea lion-like birds; their shells are very easily broken by eiders. In addition, crabs become prey for some mammals, for example, roaches or striped raccoons. These animals effortlessly dig crabs out of their burrows. DID YOU KNOW THAT...
