This wonderful photograph, which was one of the ten highly commended entrants in the 2012 New Scientist Eureka Prize for Science Photography, captures an extremely special event. That chartreuse green insect is unfurling from its little egg to add to a slowly swelling captive population of Lord Howe Island stick insects - one of the rarest, and largest, insects in the world - at Melbourne Zoo. It will grow up to be a flightless, nocturnal insect that stretches up to 12 cm long, its solid, shiny black or rust-coloured body weighing up to 25 grams. Sir David Attenborough loves them.

In the 19th century, the Lord Howe Island stick insect (Dryococelus australis) was a common site on its native Lord Howe Island, which is located about 700 km east of Port Macquarie in New South Wales. So common were these insects, that fishermen would use them as bait and their wives would dread running into one on a trip to the outback toilet. Then mice were introduced to the island in the 1880s, and black rats hitched a ride on the British vessel S.S. Makambo in 1918, which led to the decimation of the endemic stick insect population. Soon, sightings of the Lord Howe Island stick insect declined to such an extent that by 1920, not a single one was found, and by 1960, they were declared extinct. Twelve other invertebrate species and five bird species were also driven to extinction because of the rats.

They were rumoured, however, to be living in on Ball’s Pyramid, a super-sheer volcanic stack about 20 km from Lord Howe Island, which measures around 550 metres high, 300-metres wide and one-kilometre-long. It not only sounds hellishly difficult to explore - there's barely anywhere flat to stand on it - in 1984, the Lord Howe Island Board made it illegal for anyone to climb it except specifically for scientific work. It took over ten years for a successful application to be made, and the proposal certainly wasn't to find the big, black trophy many explorers had tried to locate on Ball's Pyramid before the ban. The team behind the application, Australian scientists David Priddel and Nicholas Carlile from the NSW Department of Environment, Climate Change and Water; ranger Dean Hiscox; entomologist Stephen Fellenberg and entomology curator Margaret Humphrey from the Macleay Museum at the University of Sydney, travelled to Ball's Pyramid in 2001 to prove, once and ford all, that the Lord Howe Island stick insect was extinct. “David and I decided the only way to mount a trip to Ball’s Pyramid was to take some entomologists, and to prove the things weren’t there,” Carlile says.

One day, when the conditions were finally calm enough to navigate their little boat through the choppy waters around the edge of Ball's Pyramid, the team climbed about 150 m up the sheer rock face to find a couple of oversized crickets. Dizzy and dehydrated, they climbed back down to the boat, and passed a single Melaleuca howeana - a dense, short and hardy bush native to Lord Howe Island - that grew in a small crevice containing what was likely to be the only patch of soil on the whole formation. And there sat, as Carlile described it, "a large poo". Upon revisiting the bush the day after, the team were astounded to find two huge stick insects, quietly straddling the bush. “It was just phenomenal," says Carlile. "Even 12, 13 years later it is one of the highlights of my life."

It turns out this little bush was feeding the entire population of Lord Howe Island stick insects on Ball's Pyramid - 24 individuals in total - providing food and a soft soil surface for them to lay their eggs in. This little bush, and those that no doubt preceded it, had been sustaining the only Lord Howe Island stick insects in the world for half a century. As to how the hefty insects travelled over 20 km of ocean from Lord Howe Island to make Ball's Pyramid their new home, Carlile suspects they floated over as discarded fish bait, or were unwittingly carried by a kind of seabird, called the common noddy, in nesting material. Since the rediscovery of this species, numerous eggs and breeding pairs have been brought to the Australian mainland to breed in captivity. Melbourne Zoo now has around 1 000 adults and 20 000 eggs. A captive colony was also established on Lord Howe Island in 2009. "It is quite a strange thing to have the species that close to its original habitat," says Carlile. "They were known to seek daytime refuge in the hollow sections of Banyan Figs (as is the backdrop to the enclosure pictured below) - but due to the presence of rats and mice beyond the mesh of their current quarters,they are obliged to remain there until we ... eradicate the rodents. Hopefully they will get their chance to regain their realm in the coming years."

The plan is to eradicate the rats and mice from conservation areas on Lord Howe Island in 2015, and then reintroduce the captive-bred stick insects, and their natural predators - a sub-species of boobook owl. This AU$9 million project has just been approved last month, as announced by Federal Environment Minister Tony Burke and NSW Environment Minister Robyn Parker. According to the government press release, they hope to wipe out more than 130,000 rodents using poison baits, some dropped by air, in allocated conservation areas. Special 'arks' will be used to protect native, endangered species until the rodents are gone.

"On Lord Howe Island, the original control for the phasmid [stick insect] was a sub-species of the boobook owl that was wiped out by an introduced owl (Tasmanian/mainland masked owl), brought in to 'control' the introduced black rat," says Carlile. "Our intention with the rodent eradication is to remove the masked owl - through secondary poisoning from them consuming rats and mice, and then selective shooting - as it not only takes up the niche of the original owl, but also preys on seabirds, the endemic Lord Howe Island woodhen and native Lord Howe Island currawong. Around the same time of the phasmid releases (probably of eggs) we would look to establish a population of boobook owl. The most likely candidate is a hybrid Norfolk Island/New Zealand species that has limited breeding habitat on Norfolk Island and is in need of further conservation for its survival. This species would be introduced by moving near-fledged owl chicks from Norfolk and rearing them to release on Lord Howe Island."

You can read more about the Lord Howe Island stick insect in my new book, Zombie Tits, Astronaut Fish and Other Weird Animals, which is available for pre-order now.

Here's a video of Rohan Cleave's hatching Lord Howe Island stick insect:

Lord Howe Island Stick Insect hatching from Zoos Victoria on Vimeo.