Coconut Crab and Rhinoceros beetle
The coconut crab and the coconut rhinoceros beetle are also resident on the Philippine archipelago. Both representatives are palm pests - however, palm pests with a fascinating biological feature profile. While the coconut crab, the greatest land crab of the world, has already become very rare and is a threatened animal in the Philippines - the smaller coconut rhinoceros is still a great danger for the palm plantations in South East Asia.
The Coconut Crab
The male of the coconut crab (names Lat.: birgus latro/ English: robber crab or coconut crab/in the Philippines: tatus, umang; alimangong lupa reaches) reaches a maximum weight of 3 kg and a leg span up to one meter. In its dimensions it is only surpassed by the Japanese sea and spider crab which can get up to 17 kg and a leg span of four meters. The color of the body differs from region to region: The striking colour range includes crimson -blue and orange-brown.
The up to 40 cm long body is roughly divided by a front section and a relatively big abdomen. In the front section are the eating and breathing organs as well as the reddish - weakly developed - stalked eyes. The breathing organs are modified gill tissues - caused by the evolution from a sea animal to a terrestrial animal – and must be kept moistly. Despite gills the fully-grown animal cannot consume oxygen from the sea water; sooner or later it would be drowned. The lakeside is only visited to regulate the salt balance or to release larvae at high tide.
The abdomen shows in total 10 mostly strong developed strongly legs or claws. The forelegs show strong hammer tongs with which the coconut crab can open coconuts and lift up weights with more than 20 kgs. The next three couple of legs are developed at the end like pincers and allow a relatively fast running on the ground and the climbing up at palms. The smaller back legs are usually hidden under the body and are used for cleaning of the breathing organs.
During the day, the coconut hides in caves which protect it from desiccation and predators. At night, it wanders along the beach looking for nourishments like fallen coconuts. If it does not find any, it climbs also on higher palm trees and tries to pinch off nuts. Having reached the ground again by climbing backward it tries to open the shoot apertures in order to reach the white meat of the coconut. As an alternative the coconut crab takes also other organic food: Leaves, rotting fruits, dead small animals, exoskeletons of other crustaceans (calcium supply) or eggs of turtles. It feels attracted by shiny objects (pots, silverware) and sometimes it is told that this habitude gave it the German name “Palm Thief”.
As slowly growing animals the palm crabs are reaching the sexual maturity very late with the fourth year of life. The mating lasts for about 15 minutes, the stronger male puts the female onto the back. After insemination the females are carrying the eggs under their abdomen for some months and release them later in a collective action at high tide into the seawater. The larvae then swim approx. 28 days in the sea waters. They have a lot of predators. Within further 21 -28 days the larva changes to an amphibian. Up to a size of round about 3 cm the amphibian they use shells to protect their soft abdomen. Later the coconut crab gets a harder outer skeleton. The life expectancy It is assumed that the maximum life expectancy is approximately eight years.
We mentioned already that the coconut crab is relatively rare. It belongs to the threatened species of animals in the Philippines. In the Internet only small, sparsely populated islands are cited as places of finding: Olango Island (east of Cebu City), Caluya Island and Didyo Island. With regard to the small number, it should be considered that pigs, monkeys, rats, lizards and ants are eating the young crabs. However men carry the main blame for the decline. Suitable shore habitats for palm crabs have been destroyed or taken away. Moreover, the lobster similar meat is estimated as a delicacy as well as the eggs. The crab is hunted in damp nights with the help of flashlights. If they are still in the caves, smoke is used to drive them out. Sometimes if the animal is discovered on a palm tree, damp grass is tied on the palm tree. The crab then assumes that it has reached the ground and falls to the ground.
Asian experts know that there is in Asia a constant, often blind search for Aphrodisacia. So it isn't surprising that the meat of the coconut crab is also regarded as an Aphrodisacium even if the relatively weak fertility of the coconut crab doesn't give any clues for this assumption. Although there is no official market for the meat of palm crabs and legal regulations should prevent the export and import of the animals there exists nevertheless, a black market. In Japan young crabs are occasionally hold as pets. The pet-crabs should have solid cages and a portion of caution is necessary because the animals can also attack a person, if they feel threatened. "Pet" qualities are also awarded to the coconut rhinoceros beetle, our next candidate.
The Coconut Rhinoceros Beetle
With its 4 cm of body length the sturdy, black-reddish rhinoceros beetle (lat. name: oryctes rhinoceros) is unequally smaller than the coconut crab. It can be found in all parts of Southeast Asia and in the west pacific area. Modern means of transportation favoured - particularly also during the 2nd World War – its spreading. Some authors describe it as the most dangerous insect for coconut, date and oil palm plantations
Significant is the backward turned head horn which is bigger with the male. The backside of the females shows a reddish-brown hair. Rhinoceros beetles fly at night and bore into the middle ribs of the young fronds and the inflorescence to reach the fabric juice. The consequences of this tunneling and sucking are a stunted growth of the palm and reduced yields in harvest. Young palms can die. A further resultant damage is a general weakness of the palm, which then has an insufficient resistance against other pests like the nettle caterpillar or the red striped palm weevil. Adult rhinoceros beetles live about six months. After the fertilization the female puts down nearly 100 3-4 mm big, whitish brown eggs in tree stumps, sawdust, decaying plant material or mud. After approx. two weeks gluttonous larvae develop from the eggs. The larva stage with pupations lasts for about two to three months. Fully-grown larvae have a C-shaped body form, a brown head section and legs. Mechanical (raking the palm leaves and installation of sawdust traps), chemical (insecticides) or biological methods (virus infection the male) are used to expel the rhinoceros beetles. Quite important is an adequate prophylaxis, i.e. field sanitation and particularly the avoidance of rotting biological scraps.
Hanewald (1) gives the information that in Culion (northern Palawan) children are collecting the beetles in order to sell them to Chinese dealers. They feed the little black monsters with sweet juices, and later they resell them to Japan. Here coconut rhinoceros beetles are held as pets. Anyway Japan is an important country with regard to beetles. In 2001 about 319,000 rhinoceros beetles and 364,000 stag beetles (2) were exported to Japan and there is already a danger that the imported beetles could threaten the native beetles.
© Wolfgang Bethge, 2005
(1) Roland Hanewald, Inselfieber, p. 203
(2) 680.000 beetles imported in 2001, trade monitor says in Japan Times, 7-30-2002