''Dryococelus australis'', also known as the Lord Howe Island stick insect, Lord Howe Island phasmid or, locally, as the tree lobster, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of stick insect that lives in the Lord Howe Island Group. It is the only member of the monotypic genus ''Dryococelus''. Thought to be extinct by 1920, it was rediscovered in 2001. Although it had been extirpated from Lord Howe itself, a remnant population of 24 individuals was rediscovered on the sea stack of Ball's Pyramid, and the species has been called "the rarest insect in the world".

Anatomy and behaviour

Adult Lord Howe Island stick insects can measure up to in length and weigh , with

male Male (Planet symbols, symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or Egg cell, ovum, in the process of fertilisation. A male organism cannot sexual repro ...

s 25% smaller than

female An organism's sex is female ( symbol: ♀) if it produces the ovum (egg cell), the type of gamete (sex cell) that fuses with the male gamete (sperm cell) during sexual reproduction. A female has larger gametes than a male. Females and ...

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) and this quality has allowed the species to survive when they are low in numbers.

Extinction

The stick insects were once very common on Lord Howe Island, 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 to become established. After 1920, no stick insects could be found. The species was declared extinct.

Rediscovery

In 1964, a team of climbers visiting Ball's Pyramid, a rocky sea stack south-east of Lord Howe, discovered a dead stick insect. In 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, bottlebrushes or tea-trees (although the last name is also applied to species of '' Leptospermum''). They ...

'' 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 New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

National Parks and Wildlife Service returned to Ball's Pyramid and collected two breeding pairs, one destined for a private breeder in

Sydney Sydney is the capital city of the States and territories of Australia, state of New South Wales and the List of cities in Australia by population, most populous city in Australia. Located on Australia's east coast, the metropolis surrounds Syd ...

and the other sent to the Melbourne Zoo.

Conservation

After initial difficulties, the insects were successfully bred in captivity in

Melbourne Melbourne ( , ; Boonwurrung language, Boonwurrung/ or ) is the List of Australian capital cities, capital and List of cities in Australia by population, most populous city of the States and territories of Australia, Australian state of Victori ...

. The ultimate goal was to produce a large population for reintroduction to Lord Howe Island, provided that a project to eradicate the invasive 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 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 2012, the Budapest Zoo was the first zoo outside of Australia to reproduce the insects. 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 (biology), family, Myrtaceae and is Endemism, endemic to the Lord Howe Island, Lord Howe Island group, off the east coast of Australia. It is common in exposed a ...

''. 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. 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 to protect the island ecology and potentially reintroduce ''D. australis.'' plans are being made to reintroduce the insects to Blackburn Island, an islet in the Lord Howe lagoon, to test the potential for reintroduction to the larger island. In 2025, the Prague Zoo joined the conservation program. The zoo became the sixth institution in the world to create living conditions for ''D. australis'' and the third to put them on display. The new "Ball's Pyramid exhibit" also includes greenhouses and garden beds for cultivating the plants used to feed the insects.

Genetic

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.

References

External links

* *
Sticky, a short film on the rediscovery of the Lord Howe Island Stick InsectVideo of Stick insect hatching
by David Priddel, at the Foundation for National Parks & Wildlife
Sticks and stones
article, '' Sydney Morning Herald'', 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 Australia’s principal public service broadcaster. It is funded primarily by grants from the federal government and is administered by a government-appointed board of directors. The ABC is ...

Phylogenetic study on ''Dryococelus australis''
{{Taxonbar, from1=Q14626919 Phasmatidae Monotypic insect genera Insects of Lord Howe Island Critically endangered insects Insects described in 1855 Insects of Australia Phasmatodea genera