''Dryococelus australis'', commonly known as the Lord Howe Island stick insect or tree lobster,
is a
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
stick insect
The Phasmatodea (also known as Phasmida, Phasmatoptera or Spectra) are an order of insects whose members are variously known as stick insects, stick-bugs, walking sticks, stick animals, or bug sticks. They are also occasionally referred to as ...
that lives on the
Lord Howe Island Group
Lord Howe Island (; formerly Lord Howe's Island) is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, part of the Australian state of New South Wales. It lies directly east of mainland Port ...
. It is the only member of the
monotypic genus ''Dryococelus''. Thought to be extinct by 1920, it was rediscovered in 2001.
It is
extirpated in its largest former habitat,
Lord Howe Island
Lord Howe Island (; formerly Lord Howe's Island) is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, part of the Australian state of New South Wales. It lies directly east of mainland P ...
, and has been called "the rarest insect in the world", as the rediscovered population consisted of 24 individuals living on the small islet of
Ball's Pyramid
Ball's Pyramid is an erosional remnant of a shield volcano and caldera lying southeast of Lord Howe Island in the Pacific Ocean. It is high, while measuring in length and only across, making it the tallest volcanic stack in the world. Bal ...
.
Anatomy and behaviour
![Dryococelus australis 02b Pengo](https://upload.wikimedia.org/wikipedia/commons/2/2c/Dryococelus_australis_02b_Pengo.jpg)
Adult Lord Howe Island stick insects can measure up to in length and weigh , with
male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
s 25% smaller than
female
Female (Venus symbol, symbol: ♀) is the sex of an organism that produces the large non-motile ovum, ova (egg cells), the type of gamete (sex cell) that fuses with the Sperm, male gamete during sexual reproduction.
A female has larger gamet ...
s. They are oblong in shape and have sturdy legs. Males have thicker thighs than females. Unlike most
phasmida, the insects have no wings.
The behaviour of this stick insect is highly unusual for an insect species, in that the males and females form a bond in some pairs.
The females lay eggs while hanging from branches. Hatching can happen up to nine months later. The
nymphs are first bright green and active during the day, but as they mature, they turn black and become nocturnal.
Reproduction can happen without the presence of males (
parthenogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
) and this quality has allowed the species to survive when they are low in numbers.
History and conservation
The stick insects were once very common on
Lord Howe Island
Lord Howe Island (; formerly Lord Howe's Island) is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, part of the Australian state of New South Wales. It lies directly east of mainland P ...
, where they were used as bait in fishing. They were believed to have become extinct soon after the supply ship ran aground on the island in 1918, allowing
black rats
The black rat (''Rattus rattus''), also known as the roof rat, ship rat, or house rat, is a common long-tailed rodent of the stereotypical rat genus ''Rattus'', in the subfamily Murinae. It likely originated in the Indian subcontinent, but is n ...
to become established. After 1920, no stick insects could be found.
[ However, in 1964, a team of climbers visiting ]Ball's Pyramid
Ball's Pyramid is an erosional remnant of a shield volcano and caldera lying southeast of Lord Howe Island in the Pacific Ocean. It is high, while measuring in length and only across, making it the tallest volcanic stack in the world. Bal ...
, a rocky sea stack
A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks are formed over time by wind and water, processes of coastal geomorphology. ...
south-east of Lord Howe Island, discovered a dead Lord Howe Island stick insect. During subsequent years, climbers found a few more fresh carcasses, but expeditions to find live specimens were unsuccessful.
In 2001, Australian scientists David Priddel and Nicholas Carlile hypothesised that there was sufficient vegetation on the islet to support a population of the insects, and, with two assistants, travelled there to investigate further. They scaled 120 metres of grassy, low-angled slope, but found only crickets. On their descent, the team discovered large insect droppings under a single ''Melaleuca
''Melaleuca'' () is a genus of nearly 300 species of plants in the myrtle family, Myrtaceae, commonly known as paperbarks, honey-myrtles or tea-trees (although the last name is also applied to species of '' Leptospermum''). They range in size ...
'' shrub growing in a crevice approximately 100 metres above the shoreline. They deduced that they would need to return after dark, when the insects are active, to have the best chance of finding living specimens. Carlile returned with local ranger Dean Hiscox and, with a camera and flashlights, scrambled back up the slopes. They discovered a small population of 24 insects living beneath the ''Melaleuca'' shrub amongst a substantial build-up of plant debris.
In 2003, a research team from New South Wales
)
, nickname =
, image_map = New South Wales in Australia.svg
, map_caption = Location of New South Wales in AustraliaCoordinates:
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, es ...
National Parks and Wildlife Service returned to Ball's Pyramid and collected two breeding pair
Breeding pair is a pair of animals which cooperate over time to produce offspring with some form of a bond between the individuals.Gaston, A. J.The evolution of group territorial behavior and cooperative breeding" The American Naturalist 112.988 ...
s, one destined for a private breeder in Sydney
Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mountain ...
and the other sent to the Melbourne Zoo
Melbourne Zoo is a zoo in Melbourne, Australia. It is located within Royal Park in Parkville, approximately north of the centre of Melbourne. It is the primary zoo serving Melbourne. The zoo contains more than 320 animal species from Austra ...
. After initial difficulties, the insects were successfully bred in captivity in Melbourne
Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...
. The ultimate goal was to produce a large population for reintroduction to Lord Howe Island, providing that a project to eradicate the invasive
Invasive may refer to:
*Invasive (medical) procedure
*Invasive species
*Invasive observation, especially in reference to surveillance
*Invasively progressive spread of disease from one organ in the body to another, especially in reference to cancer ...
rats was successful. In 2006, the captive population of insects numbered about 50 individuals, with thousands of eggs still to hatch. In 2008, when Jane Goodall
Dame Jane Morris Goodall (; born Valerie Jane Morris-Goodall on 3 April 1934), formerly Baroness Jane van Lawick-Goodall, is an English primatologist and anthropologist. Seen as the world's foremost expert on chimpanzees, Goodall is best know ...
visited the zoo, the population had grown to 11,376 eggs and 700 individuals, 20 of which were soon after returned to a special habitat on Lord Howe Island. , the Melbourne Zoo had reportedly bred over 9,000 of the insects, including 1,000 adult insects, plus 20,000 eggs.
In 2014, an unauthorised climbing team sighted live stick insects near the summit of Ball's Pyramid, in a thicket of sedge plants rooted in very thin soils at an altitude of 500 metres, suggesting that the insect's range on the island is more widespread than previously thought, and that its food preferences are not limited to ''Melaleuca howeana
''Melaleuca howeana'', commonly known as tea tree, is a plant in the myrtle family, Myrtaceae and is endemic to the Lord Howe Island group, off the east coast of Australia. It is common in exposed areas, on cliffs and ridges, occasionally fo ...
''.
By the beginning of 2016, Melbourne Zoo had hatched 13,000 eggs, and had also sent eggs to the Bristol Zoo in England, the San Diego Zoo in the United States, and the Toronto Zoo in Canada, to establish distinct insurance populations.
A 2017 study comparing DNA sequences of phasmids originating from Ball's Pyramid with those from museum specimens from Lord Howe Island showed that the Ball's Pyramid sequences differ from those of Lord Howe Island by a degree comparable to variation within the museum specimens, despite some morphological differences between the two groups. This confirms that the two populations represent the same species. The genome was found to be very large in size (over 4 Gb) and is probably hexaploid
Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...
.
In 2018 it was announced that the CEO of the Lord Howe Island Board had approved a plan to exterminate the black rat population on Lord Howe Island and reintroduce ''D. australis.''
See also
*Giant weta
In folklore, giants (from Ancient Greek: '' gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fro ...
* Lazarus taxon
*Threatened fauna of Australia
Threatened fauna of Australia are those species and subspecies of birds, fish, frogs, insects, mammals, molluscs, crustaceans and reptiles to be found in Australia that are in danger of becoming extinct. This list is the list proclaimed under t ...
References
External links
*
*
Sticky, a short film on the rediscovery of the Lord Howe Island Stick Insect
Video of Stick insect hatching
by David Priddel, at the Foundation for National Parks & Wildlife
The Foundation for National Parks & Wildlife is an Australian not-for-profit, non-governmental organisation that was incorporated on 29 June 1970. Its purpose is to foster the protection of Australia's native plants, animals and cultural heritag ...
Sticks and stones
article, ''Sydney Morning Herald
''The Sydney Morning Herald'' (''SMH'') is a daily compact newspaper published in Sydney, New South Wales, Australia, and owned by Nine. Founded in 1831 as the ''Sydney Herald'', the ''Herald'' is the oldest continuously published newspaper i ...
'', 18 October 2003 (with picture)
Giant stick insect rediscovered
science news 14 February 2001 at the Australian Broadcasting Corporation
The Australian Broadcasting Corporation (ABC) is the national broadcaster of Australia. It is principally funded by direct grants from the Australian Government and is administered by a government-appointed board. The ABC is a publicly-own ...
Phylogenetic study on ''Dryococelus australis''
{{Taxonbar, from1=Q152856, from2=Q14626919
Critically endangered insects
Insects of Lord Howe Island
Insects described in 1855
Phasmatodea
Insects of Australia