Tree lobster

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Tree lobster
Groomed male tree lobster (Dryococelus australis)

Groomed male tree lobster ( Dryococelus australis )

Systematics
Order : Ghost horror (Phasmatodea)
Subordination : Verophasmatodea
Family : Phasmatidae
Subfamily : Lonchodinae
Genre : Dryococelus
Type : Tree lobster
Scientific name of the  genus
Dryococelus
Gurney, 1947
Scientific name of the  species
Dryococelus australis
( Montrouzier , 1855)
Female tree lobster

The tree lobster ( Dryococelus australis ) is an insect from the order of the stick insects (Phasmatodea) and the only member of the genus Dryococelus . Contrary to the German name, the insect is not related to the lobsters ( Homarus ) of the crustaceans .

The tree lobster is endemic to the Australian Lord Howe Island and was considered extinct for a long time until living specimens were found on the small rock island Ball's Pyramid , which belongs to the Lord Howe group of islands .

features

Adult tree lobsters are wingless, mostly completely black, rarely dark brown insects. Only specimens or animals under artificial light show a rather red-brown color. The massive body is almost free of thorns or spines. Only the males have two strong, long thorns on the thighs ( femurs ) of the hind legs, as can also be found in many other representatives of the Eurycanthini tribe . At 100 to 112 millimeters, they remain slightly smaller than the females, which reach a length of 120 to 133 millimeters. The abdomen of the females ends in a beak-shaped, secondary laying spine, which surrounds the genital organs including the actual laying apparatus ( ovipositor ) consisting of appendages of the eighth and ninth abdominal segment . Compared with the laying spine of other representatives of this subfamily, the upper part, the eighth sternum, known as the subgenital plate or operculum, is shorter. As a result, the upper part of the laying spine is surmounted by the extended tenth abdominal tergum on the underside.

Way of life and reproduction

The nocturnal phasmids hide in cavities during the day and only come out at night to eat their food plants. The males are aggressive towards one another and often mate with the females, some of whom even guard them. Like other representatives of the subfamily, the animals often sit on top of each other in hiding places. The females lay clutches of nine to ten eggs in the ground about every ten days. A total of around 300 eggs are produced per animal. The eggs, which are initially pale beige, become increasingly darker on permanent contact with the moist soil, until they are dark brown or almost black. After six to seven months, the 16 to 22 millimeter long nymphs hatch from them . They are light green at first, but get darker with each moult . So they first turn light brown, then dark brown, until they are finally black as an imago . The natural predator was the Lord Howe cuckoo owl , a subspecies of the New Zealand cuckoo owl endemic to Lord Howe Island . This was exterminated by the Tasmanian barn owl introduced to control rats .

Original distribution and apparent extinction

The tree lobster was originally found all over Lord Howe Island, 580 kilometers east of Australia. The species therefore bears the common name "Lord Howe Island stick insect" in the English-speaking world . However, the islanders called it "land lobster", from which the German name "tree lobster" is probably derived. The animals that were originally common were used as fishing bait. When the supply ship SS Makambo ran aground on Lord Howe Island on June 14, 1918 , rats from the wrecked ship came to the island. These spread on the island with catastrophic consequences for the endemic fauna . The tree lobster population was decimated to such an extent that no more animals were found by 1920. Since 1930 it has been assumed that the species was one of 13 invertebrate species to be exterminated by the rats. Around 1960 it was declared "extinct".

Rediscovery and Protection

View of Ball's Pyramid , where the last tree lobsters were found

After rock climbers discovered one dead tree lobster on the small rock island Ball's Pyramid , 23 kilometers southeast of Lord Howe Island, in 1964 and two more in 1969, researchers examined the barren rock more closely in 2001. They found two females and a female nymph. In a further investigation in 2002 , 24 specimens were found on a small rock terrace of 6 mx 30 m on which a small tea tree of the species Melaleuca howeana , native to Lord Howe Island , stood, including only two males. How this population got to this rocky island is not definitively clear. The animals could have washed up on driftwood or inadvertently got onto the island on nesting material brought by the Noddise Tern . There is also the possibility that fishermen brought the first animals with them as bait.

In 2003, Stephen J. Fellenberg removed two pairs from the population and started a breeding program in order to maintain a sufficiently large population and to reintroduce the tree lobster to Lord Howe Island as soon as it is cleared of the rats.

This breeding program at Melbourne Zoo is very successful after initially having major problems. In 2005 there were already more than one hundred tree lobsters in captivity, which, in addition to the tea tree already mentioned, also accept large-leaved fig ( Ficus macrophylla ), sprouting dwarf gorse ( Chamaecytisus proliferus ), blackberries , lemon trees and other forage plants. By 2008 the population had grown to 450 animals, in early and mid-2012 to 9,000, including 1,000 adults, and around 20,000 eggs.

In 2009 the first 20 specimens were returned to a specially protected habitat on Lord Howe Island. As part of the Lord Howe Island Rodent Eradication Project, all rats and mice should be exterminated by using poison bait, after which the tree lobsters should also be freely established on the island again. The dropping of 42 tons of bait with the active ingredient Brodifacoum by helicopters in distant areas of the island sparked a dispute among the islanders about the pros and cons of this action, which even a decision that was narrowly made for the supporters could not resolve. Another plan was to establish a hybrid of the subspecies of the New Zealand cuckoo owl on the Norfolk Island and the New Zealand native subspecies as a natural enemy , for which the Tasmanian barn owl was to be exterminated on Lord Howe Island.

Systematics

Morphological differences between males from Lord Howe Island (left) and males from the breeding program from Ball's Pyramid (right)

In 1855 Montrouzier described the genus Karabidion with the new species Karabidion micranthum (now Eurycantha micrantha ) and Karabidion australe , the tree lobster. He also transferred the Eurycantha horrida, described by Boisduval in 1835, to this genus. All species were transferred to the older genus Eurycantha by Westwood as early as 1859 , making Karabidion a synonym for Eurycantha . In 1904 Kirby wrongly described a male tree lobster nymph as a new species. He placed this in the genus Eubulides , which is now part of the Heteropterygidae family , and named it Eubulides spuria . The corresponding holotype could not be found for a time, but was rediscovered in 2006 in the Natural History Museum in London . The species had already been synonymous with Dryococelus australis . The generic name Dryococelus , which is valid today for the tree lobster, goes back to Gurney , who established this monotypical genus in 1947. The type material of Dryococelus australis , a male and a female, which were deposited as syntypes in the Institut Sainte Marie in Saint-Chamond in France , is considered lost.

Only in 2008 was it proven that the tribe Eurycanthini is actually polyphyletic . The similarity between the "tree lobsters" of Lord Howe, New Guinea and New Caledonia goes back to convergent evolution . Sister group of Dryococelus are the Australian giant stick insects of the genus Eurycnema (compare e.g. Eurycnema goliath ).

The animals rediscovered on Ball's Pyramid show clear morphological differences to those before the extinction on Lord Howe Island. By comparing the genetic make-up of animals from the Melbourne Zoo's breeding program and old museum specimens, it was found that they are the same species. The samples differed by less than 1%, which is within the variation of the museum specimens.

swell

  1. ↑ a b c d e Paul D. Brock & Jack W. Hasenpusch : The complete field guide to stick and leaf insects of Australia , Csiro Publishing, Collingwood, Auaralia, 2009, pp. 74–75, ISBN 978-0-643- 09418-5
  2. ↑ a b c d scientificamerican.com : Becky Crew: Lord Howe Island stick insects are going home , August 22, 2012, in English, accessed August 31, 2012
  3. ↑ a b c www.heise.de - Article by Wolf-Dieter Roth from July 19, 2006 about tree lobsters on the Telepolis site
  4. ↑ youtube.com : Act Wild for Lord Howe Island Stick Insects , April 18, 2012, in English, accessed June 2, 2012
  5. ↑ An island argues over rat hunting. In: orf.at , February 9, 2016, accessed on November 21, 2017.
  6. ↑ a b Alexander S. Mikheyev, Andreas Zwick, Michael JL Magrath, Miguel L. Grau, Lijun Qiu, You Ning Su, David Yeates: Museum Genomics Confirms that the Lord Howe Island Stick Insect Survived Extinction . In: Current Biology . October 5, 2017, doi : 10.1016 / j.cub.2017.08.058 .
  7. ↑ geocurrents.info : Martin W. Lewis: Lord Howe Island: Return of the Tree Lobster , March 8, 2010, in English, accessed June 2, 2012
  8. ^ Paul D. Brock: Phasmida Species File Online . Version 2.1 / 4.1. (accessed on September 1, 2012)
  9. ↑ Thomas R Buckley, Dilini Attanayake, Sven Bradler (2009): Extreme convergence in stick insect evolution: phylogenetic placement of the Lord Howe Island tree lobster. Proceedings of the Royal Society Series B vol. 276 no. 1659: 1055 - 1062. doi : 10.1098 / rspb.2008.1552

Web links

Commons : Tree Lobster  - album with pictures, videos and audio files