Palm thief
| Palm thief | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Palm thief |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name of the genus | ||||||||||||
| Birgus | ||||||||||||
| WE Leach , 1815 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Birgus latro | ||||||||||||
| ( Linnaeus , 1767) |
The coconut crab ( Birgus latro ), also coconut robbers , in English-speaking countries also ganjo crab or coconut crab called, is one of order of decapods belonging (Decapoda) crustaceans (Crustacea) from the family of terrestrial hermit crabs (Coenobitidae). Two genera are assigned to this family : the genus Coenobita , to which about 15 species belong, and the genus Birgus , the only representative of which is the palm thief. The palm thief, which among other things is able to open a coconut , is the largest crustacean on earth living on land.
Surname
The name “palm thief”, like the English term coconut crab, may refer to the fact that the animal can climb palm trees and harvest coconuts there , which it then opens on the ground in order to consume their contents. The original scientific name Cancer latro ( latro is Latin for robber), which goes back to Carl von Linné , then apparently led to thief in the German translation . Georg Eberhard Rumpf (1627–1702), a Dutch botanist and naturalist on the Moluccan island of Ambon in the Dutch East Indies ( now Indonesia), made D'Amboinische Rariteitkamer (first edition in the Netherlands 1705, illustrated by Maria Sibylla Merian ) first known the palm thief in Europe.
Characteristics of palm thieves
anatomy
When fully grown, palm thieves can reach a body length of up to 40 centimeters and a weight of up to 4 kilograms. The span of the legs can be up to one meter. The palm thief is thus the largest land-living representative of the arthropods . Only in the water, where the body is carried by the water, do decapods get bigger. Male specimens of the Japanese giant crab ( Macrocheira kaempferi ), which is considered to be the largest crustacean, have a leg span of almost four meters.
Palm thieves have half sunken, red complex eyes on short eye stalks. Their body color varies from island to island between blue-purple and red-orange. The males are usually larger than the females.
As is typical for decapods, the body is divided into a front section ( cephalothorax ), on which the ten legs are located, and a rear section, the abdomen or pleon . At the end of the foremost pair of legs there are scissors of different sizes and specialized in their function, the left of which is always the larger: So Birgus is like z. B. also left-handed hermit crabs , "monostrophic left-sheared": The larger left one should be "more than twice as large as the other". With the differently usable scissors, the palm thief is able to open coconuts (by applying one of the scissors to the three germ holes at the upper end of the nut) and to lift objects weighing up to 28 kilograms. The legs are mainly used by the palm thief for locomotion. Because of the scissors and legs, palm thieves are able, among other things, to climb vertically up rough tree trunks. The last pair of legs is very small and is only used by the palm thief to clean the air breathing organs.
Although the palm thief belongs to the land hermit crabs, only young and adolescent animals use snail shells to protect their soft abdomen. Adolescent animals also occasionally use broken coconut shells if they cannot find snail shells of suitable size. Adult animals have developed other protection strategies: On the one hand, palm thieves curve their abdomen under the front body to protect them, as is the case with real crabs. Their most important protection, however, is that they store chitin and lime in the abdominal cover in the course of their development from young to adult palm thief. This hardens over time and forms a protective armor that also reduces water loss on land. The palm thieves, however, repel this protective armor at regular intervals. During the thirty days it takes for a new protective shell to form after such a molt, the palm thieves live very hidden.
breathing
Palm thieves cannot swim and would drown in the water. You breathe through gill cavities that are formed by the wide lateral edges of the carapace . These edges are called Branchiostegite . The two air cavities are at the end of the cephalothorax. They contain a tissue that is also found in gills, but unlike gills, it is designed to take in oxygen from the air and not from the water. Palm thieves use their smallest pair of legs to cleanse this respiratory organ and to moisten it with sea water. The respiratory system needs water to function, and the palm thieves ensure this by dipping their legs in the water and then stroking the spongy tissue of their Branchiostegiten. Palm thieves also drink salt water, which they bring to their mouths with the help of their legs.
In addition to this respiratory system, palm thieves have a rudimentary pair of gills. During the evolution of this species, these gills were probably used for underwater breathing. Today, however, they are no longer able to supply the animal with sufficient oxygen. There is different information about the length of time that a palm thief can survive under water, which varies between minutes and several hours, since the oxygen consumption depends on the individual condition and the stress level.
Sense of smell
The olfactory sense of crabs works differently depending on whether the molecules to be smelled are hydrophobic or hydrophilic . Crustaceans living in water have special organs on their antennae, which are known as aesthetasques or olfactory irritant threads. With these you can determine the concentration of the odor molecules and the direction from which they come. In the palm thieves, however, the aesthetasques differ significantly from those of the crabs that live in the water. They are more like the olfactory organs of insects, the sensilla - the similarity is due to a convergent evolution . Palm thieves also move their antennae in a similar way to insects in order to detect smells. They are particularly sensitive to the smell of rotting meat , bananas, and coconuts.
Distribution area
Birgus latro occurs on oceanic islands and on the smaller continental islands in the western Pacific and eastern Indian Oceans .
The largest documented population of palm thieves lives on Christmas Island in the Indian Ocean. Large populations are also found in the Cook Islands . They are particularly widespread there on Pukapuka , Suwarrow , Mangaia , Takutea , Mauke and Atiu . There is also a population on Niue . Palm thieves also live on the islands of Caroline Atoll , which is part of Kiribati , and the smaller islands of Palmerston . Populations are also found in the Seychelles , particularly on Aldabra , Îles Glorieuses , Astove Island , Assumption Island and Cosmoledo . In contrast, palm thieves have become extinct on the central islands of the Seychelles. They are also found on some Andaman and Nicobar islands in the Bay of Bengal . There is also a population on the islands of Bikini Atoll . In 1972, the animals living there were found to be contaminated with radioactive substances as a result of the atomic bomb tests in the 1940s and 1950s. Since palm thieves cannot swim as adults, these islands must have been colonized in the larval stage. However, some scientists are convinced that the distances between the islands are too great for them to be bridged during the larval stage, which lasts only 28 days. They claim that juvenile palm thieves reached them via natural rafts.
Palm thieves, on the other hand, are absent in Indonesia (with the exception of Bunaken and Togian Islands near Sulawesi ) or on the mainland of New Guinea , although these islands offer a suitable habitat and could also be populated by larvae or juvenile drifting. It is therefore assumed that palm thieves were used as a source of food by the islanders after each successful settlement, so that no populations could survive here.
habitat
The palm thief lives in crevices and sand holes along the coastline. The preferences vary from island to island and depend on the existing habitat. On the Philippine Olango Islands he lives in caves in the coral reef, while on the Guam Islands (Oceania) he digs caves in the porous limestone himself. On the islands, where he does not find any natural shelter, he digs his own sand holes on sandy or similar loose ground.
During the day, the palm thief usually stays in its cave to protect itself from dehydration and enemies. He closes the entrance to his cave with one of his scissors and thus creates the humid microclimate in his cave that is necessary for his respiratory system. In regions where many palm thieves live, some come out of their buildings during the day. Most palm thieves, however, can be seen at night as they wander along the beach in search of food.
Reproduction
The mating season for palm thieves is between May and September. The main mating season is July and August. Palm thieves mate several times during this time. Mating takes place on land and begins with an argument between male and female, in the course of which the male turns the female on its back and then mates with him. Pairing takes about 15 minutes. Shortly afterwards, the female lays the fertilized eggs, which she glues to her lower body to carry around with her for a few months. Shortly before the larvae hatch , the female visits the beach at high tide and drops the eggs into the sea water.
The larvae swim as plankton in seawater for 28 days. The greatest number fall victim to predators during this time. Most of the surviving larvae remain in the seabed for the next 28 days, during which time they use empty snail shells as protection. After that, they leave the ocean as a habitat and also lose their ability to breathe underwater. As described in the body structure section , growing palm thieves use snail shells and possibly broken coconuts to protect their abdomen before they develop their own protective armor. A palm thief is sexually mature after four to eight years . This is an unusually long development time for crustaceans.
Food and subsistence
The main source of food for the animals are the fruits of the plants in its habitat , especially the fig trees ( Ficus ), the arenga palms ( Arenga ) and the screw trees ( pandanus ). But they also eat carrion and small live animals, such as newly hatched sea turtles . It is also known that palm thieves sometimes kill careless birds such as B. Capture red-footed boobies . They also feed on the stripped skins of other crustaceans , which contain a lot of calcium , which in turn is important for the growth of their own shell. Palm thieves are jealous of one another for food . Most drag their prey into their burrows in order to be able to eat there in peace.
For a long time it was doubted that palm thieves were actually able to open coconuts. In experiments, some specimens starved to death even when surrounded by coconuts. In 1980, the German biologist Holger Rumpf, who researched the behavior of palm thieves, was able to describe for the first time in wild specimens how they open the nuts of the coconut palm ( Cocos nucifera ). If the coconut is still covered with fibers, palm thieves use the large claws on their front pair of legs to remove the fibers in strips. You always start on the side where the three germ holes are. As soon as the hard shell is exposed, hit the germ holes with the scissors until the coconut breaks open at this point. With the small scissors on the middle pairs of legs, they pull out the white coconut meat.
Palm thieves sometimes even climb palm trees to feast on the coconuts. But wrong is that Palm thieves while the coconuts tactically nip off to the fruit stems, so they can be eaten on the ground. According to Holger Rumpf's investigations, their intelligence is not sufficient for a “planned harvest”. Occasionally, however, coconuts may accidentally fall from the tree while the palm thief is tampering with them.
threat
According to the RAHA criteria, there is insufficient data to be able to decide whether the palm stealer is to be classified as an endangered species. It is therefore shown in the Red List of Endangered Species of the IUCN or World Conservation Organization as a species for which only insufficient data (“ data deficient ”) is available. The final classification dates back to 1994 and with the today defunct Category rare ( " Rare ") specified. Some reports indicate that the population is still quite high on some islands. One of the largest stocks is on Caroline Island . The population density probably varies significantly from island to island.
Young palm thieves are threatened by introduced neozoa such as rats , pigs or ants such as the yellow spinner ant ( Anoplolepis gracilipes , Yellow Crazy Ant). Adult palm thieves have no natural enemies - apart from humans. Palm thieves have poor eyesight and sense the approach of potential enemies through vibrations in the ground.
Overall, the increasing population on the islands has a negative impact on the palm thief population. Since their meat is very tasty and is considered a delicacy or aphrodisiac on many islands , the population is threatened by intensive hunting . In addition, increasing tourism and the development of the coastlines have impaired or destroyed the habitat of the palm thief. That is why the palm thief has now been placed under protection in some areas. For example, there is a minimum size that palm thieves must have reached before they can be caught.
Man and palm thief
Palm thieves, with their impressive size and strength, often hold a special position in the culture of the Pacific islanders. He applies, for example by the local inhabitants of the Tuamotu - atoll or the Ryukyu Islands traditionally considered a delicacy . The meat of palm thieves is said to resemble that of lobsters and lobsters . Among the most prized parts are the eggs inside the female palm thieves and the fat in the abdomen. Palm thieves are prepared by cooking or steaming, similar to lobsters. The recipes vary from island to island - locally palm thieves are also prepared in coconut milk.
Although palm thieves are usually not poisonous, their flesh can occasionally become poisonous - they belong to what is known as a passively poisonous crustacean. On the Tuamotu Atoll and the Ryukyu Islands, fatal poisoning is said to have occurred from eating the meat. The origin and type of the toxins is unclear, but it is assumed that the animal ingests and stores plant toxins. The different poison intake of individual animals would explain why consumption causes poisoning in some cases and not in other cases. It is also possible that it is these plant toxins that act as an aphrodisiac in lower doses - similar to the puffer fish so valued in Japan . However, palm thieves are still not a commercial commodity.
The islanders prefer to go hunting during dark nights when it has rained fresh. The best time is the three days that follow the new moon . Palm thieves can also be hunted during the day, but this usually means digging for them or smoking them out of their hiding spots.
literature
- R. Altevogt, TA Davis: Birgus latro India's monstrous crab. A study and an appeal . In: Bulletin of the Department of Marine Sciences. University of Cochin, Ernakulam 1975. ISSN 0970-9878
- P. Grubb: Ecology of terrestrial decapod crustaceans on Aldabra . In: Philosophical Transactions of the Royal Society: Biological Sciences. 1971, 260, pp. 411-416.
- EE Held: Moulting behavior of Birgus latro . In: Nature . Macmillan Journals, London 1963,200, pp. 799-800. ISSN 0028-0836
- LK Barnett, C. Emms, D. Clarke: The coconut or robber crab (Birgus latro) in the Chagos Archipelago and its captive culture at London Zoo . In: CRC Sheppard, MRD Seaward (Ed.): Ecology of the Chagos Archipelago . Linnean Society Occasional Publications. Vol. 2. Westbury Publishing, Otley 1999, pp. 273-284. ISBN 1-84103-003-1
- S. Lavery, C. Moritz, DR Fielder: Indo-Pacific population structure and evolutionary history of the Coconut Crab Birgus latro . Molecular ecology. Blackwell, Oxford 5.1996, pp. 557-570. ISSN 0962-1083
- CAN Combs, A. Alford, M. Boynton, RP Henry: Behavioral regulation of haemolymph osmolarity through selective drinking in land crabs, Birgus latro and Gecarcoidea lalandii . In: The Biological bulletin. Lancaster 182.1992, pp. 416ff. ISSN 0006-3185
- P. Greenaway, S. Morris: Adaptations to a terrestrial existence by the robber crab Birgus latro. III. Nitrogenous excretion . In: The journal of experimental biology. Cambridge 143.1989, pp. 333 ff. ISSN 0022-0949
- P. Greenaway, HH Taylor, S. Morris: Adaptations to a terrestrial existence by the robber crab Birgus latro. VI. The role of the excretory system in fluid balance . In: The journal of experimental biology. Cambridge 152.1990, p. 505ff. ISSN 0022-0949
- S. Morris, HH Taylor, P. Greenaway: Adaptations to a terrestrial existence in the robber crab Birgus latro L. VII. The branchial chamber and its role in urine reprocessing . In: The journal of experimental biology. Cambridge 161.1991, p. 315 ff. ISSN 0022-0949
- HH Taylor, P. Greenaway, S. Morris: Adaptations to a terrestrial existence in the robber crab Birgus latro L. VIII. Osmotic and ionic regulation on freshwater and saline drinking regimens . In: The journal of experimental biology. Cambridge 179.1993, p. 93 ff. (PDF download; 253 kB) ISSN 0022-0949
- MC Stensmyr, S. Erland, E. Hallberg, R. Wallén, P. Greenaway, BS Hansson: Insect-Like Olfactory Adaptations in the Terrestrial Giant Robber Crab . In: Current Biology. London 15.2005, pp. 116-121 (January 26, 2005). ISSN 0960-9822
Remarks
- ↑ Palm thief, the. Retrieved September 12, 2017 .
- ↑ Jürgen Neffe: Darwin. The adventure of life , 8th edition 2008, ISBN 978-3-570-01091-4 , p. 409.
- ↑ Bauernfeind, Ingo: Radioactive to all eternity - The fate of the Prinz Eugen . ES Mittler & Sohn, Hamburg / Berlin / Bonn 2011, ISBN 978-3-8132-0928-0 , p. 108 .
- ↑ 20 minutes: Giant crayfish eats sleeping bird. November 10, 2017. Retrieved November 10, 2017 .
- ^ Mark E. Laidre: Ruler of the atoll: the world's largest land invertebrate . In: Frontiers in Ecology and the Environment . November 1, 2017 (English, wiley.com [accessed November 10, 2017]).
Web links
- Birgus latro in the endangered Red List species the IUCN 2009. Posted by: Eldredge, 1996. Retrieved on January 4 of 2010.
