Balls Pyramid is the highest sea stack in the world (572 m) and a centre of marine birdlife - several are endemic species whilst many are migratory. It was on a ledge on this pinnacle that a species of phasmid (stick insect) that was thought extinct from 1920s was found and from a few eggs, careful breeding is returning a population to Lord Howe Island. Quite a remarkable story of species redemption!
Dryococelus australis, commonly known as the Lord Howe Island phasmid or tree lobster, is a species of stick insect that lives on the Lord Howe Island Group. It is the only member of the monotypic genus Dryococelus and was thought to be extinct by 1930, only to be rediscovered in 1964 on Ball’s Pyramid. Only 24 individuals were found to be living on Ball’s Pyramid.
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 brown, then black and become nocturnal. Reproduction can happen without the presence of males (parthenogenesis) – in which all hatched phasmids are females. This quality has allowed the species to survive when they are low in numbers.
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 SS Makambo ran aground on the island in 1918, allowing black rats to become established.
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 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 3 insects living beneath the Melaleuca shrub amongst a substantial build-up of plant debris. Another expedition the following year found 24 phasmids.
In 2003, a research team from New South Wales National Parks and Wildlife Service returned to Ball’s Pyramid and collected two breeding pairs, one destined for a private breeder in Sydney and the other sent to the Melbourne Zoo. After initial difficulties, the insects were successfully bred in captivity in Melbourne. The ultimate goal was to produce a large population for reintroduction to Lord Howe Island, providing that a project to eradicate the invasive rats was successful.
In 2008, when Jane Goodall visited the zoo, the population had grown to 11,376 eggs and 700 individuals, 20 of which were returned to an enclosure on Lord Howe Island. By April 2012, Melbourne Zoo had reportedly bred over 9,000 of the insects, including 1,000 adult insects, plus 20,000 eggs.
Parallel to this program is the eradication of rats which has been determinedly undertaken on Lord Howe Island, along with a number of other species that had previously been introduced to control the rats, including owls.
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