Dryococelus australis

Anatomy and behaviour

Adult Lord Howe Island stick insects can measure up to 15 centimetres (6 in) in length and weigh 25 grams (1 oz), with females 25% smaller than males. They are oblong in shape and have sturdy legs. Males have thicker thighs than females. Unlike most phasmids, the insects have no wings, but are able to run quickly.

The behaviour of this stick insect is highly unusual for an insect species, in that the males and females form a bond.

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 facility 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, where they were used as bait in fishing. They became extinct there soon after black rats were introduced to the island in 1918 when the supply ship SS Makambo ran aground. The last one was seen on the island in 1920, and after that the species was thought to be extinct. In 1964, a team of climbers visiting Ball's Pyramid, a rocky sea stack 23 kilometres (14 mi) south-east of Lord Howe Island, discovered a dead Lord Howe Island stick insect. During subsequent years, a few more dead insects were discovered, but expeditions to find live specimens were unsuccessful.

In 2001, Australian scientists David Priddel and Nicholas Carlile hypothesized that there was sufficient vegetation on the islet to support a population of the insects, and with two assistants travelled to the island to investigate further. They scaled 500 feet of rock, but only found crickets. On their descent, the team discovered large insect droppings under a single Melaleuca shrub growing in a crevice approximately 100 m (330 ft) 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, scaled the heights again. They discovered a small population of 24 insects living amongst a substantial buildup of plant debris beneath the Melaleuca shrub.

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 2006, the captive population of insects was about 50 individuals, with thousands of eggs waiting 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. As of April 2012, the Melbourne Zoo has reportedly bred over 9,000 of the insects, including 1,000 adult insects, plus 20,000 eggs.

By the beginning of 2016, Melbourne Zoo had hatched 13,000 eggs, and had sent eggs to the Bristol Zoo in Europe, the San Diego Zoo in the United States, and the Toronto Zoo in Canada to establish distinct insurance populations.