The Lord Howe Island Phasmid:
an extinct species reborn
By David Priddel

Lord Howe island's most famous resident is undoubtedly the Lord Howe Woodhen Gallirallus sylvestris, a species saved from the very brink of extinction by a concerted conservation campaign spanning several decades. The Foundation for National Parks & Wildlife was instrumental in initiating the woodhen recovery project, and has provided on-going financial support.

But the woodhen may be about to surrender the prominence that it has enjoyed to another remarkable creature of these World Heritage-listed islands.

Towering from the waters of the Pacific Ocean, 23 kilometres to the south-east of the main island of Lord Howe, is Balls Pyramid - a volcanic spire that rises abruptly to a height of 550 metres above the ocean.The near vertical rock walls of the Pyramid tower upward to a summit that is a mere four metres wide.

Nicholas Carlile of the NSW Department of Environment and Conservation examines an adult female phasmid "Eve". She has laid over 120 eggs in the past 9 months and is still going strong. Photo Patrick Honan.

This, the tallest sea-stack in the world, is home to tens of thousands of seabirds. Living among this thriving rookery is an animal that was thought to be lost forever - the Lord Howe Island Stick-insect Dryococelus australis.

Growing to a length of 12 cm and with a body exceeding one cm in width, this giant insect, also known as the Lord Howe Island Phasmid, is a true heavyweight of the arthropod world. Its body is the colour and length of a large cigar.

Once common in the forests of Lord Howe Island, it disappeared without trace in the 1920s. Black Rats, Rattus rattus, were the cause of the insects' demise. The rats, which landed in 1918 when the supply ship Makambo ran aground, simply feasted on the defenceless insects until none were left.

During the 1960s, hopes that there might be surviving stick-insects were rekindled when rock climbers discovered some newly dead remains on Balls Pyramid. Barren and largely devoid of vegetation, Balls Pyramid contains none of the luxuriant forests that were the habitat of this species on the main island. Was it at all plausible that a population of large, herbivorous insects could survive on this remote, desolate outpost?

In February 2001, we landed a small team of scientists on the Pyramid to search for the elusive insect. Sea conditions around Balls Pyramid can be treacherous, but fortuitously, the seas abated long enough for us to get ashore safely. Leaping onto rocks from a boat in surging seas took a level of nerve and seamanship few would wish to test. Swimming ashore is possible but involves running the gauntlet of sharks that infest these rich waters.

A nymph on its food bush, Melaleuca howeana.Photo Nicholas Carlile

After we established a base camp, we began searching every shred of vegetation for evidence of the elusive stick-insect. Although we found other interesting species, we returned to camp at dusk without sighting our quarry. We were encouraged, however, by the discovery of large insect droppings (referred to by entomologists as “frass”) under a single Melaleuca howeana shrub, about 100 m above the shoreline.

Historical records indicate that this stick-insect is nocturnal. We surmised that our best chance of sighting one would be to climb the Pyramid at night and search the shrub where we had earlier found the frass. Nicholas Carlile, a NPWS scientist, and Dean Hiscox, a local ranger, volunteered to make the difficult ascent. Treacherous climbing conditions necessitated that they travelled light. Equipped only with head torches, a spare battery and a compact camera they made the assault.

Approaching their destination they were resigned to finding nothing more unusual than a large cricket. Neither was prepared for what they saw. Glistening in the torchlight, straddling the outer leaves of the melaleuca bush, were two of the largest insects imaginable. They were looking at a species that had not been seen alive for 80 years.

The sheer elation of this experience had them jumping for joy like 6-year-olds at a birthday party. Some precious data was collected and a few photos snapped before the pair began the cautious descent back to base camp.

The next day we revisited the bush, then searched the rest of the Pyramid. We discovered that the bush was growing in a small crevice where water was seeping through cracks in the underlying rocks. This moisture supported relatively lush plant growth which had, over time, resulted in a build up of plant debris, several metres deep. This was the moist, dark refuge where the stick-insects sheltered during the day.

We subsequently discovered that this type of habitat occurred nowhere else on the Pyramid. The insects were restricted to a single bush and the population probably did not exceed 20 individuals. The Lord Howe Island Phasmid is arguably the rarest insect in the world, and their future on Balls Pyramid is precarious to say the least.

Two years later, in February 2003, we revisited the Pyramid. This time it was not to search for the stick-insects, but to collect them. The aim was to establish a captive colony back on the mainland. Should a calamity then befall the tiny population on Balls Pyramid, the species would not be lost forever. Two males and two females were collected and carefully transferred to the mainland. One pair went to a private breeder in Sydney, the other to Melbourne Zoo.

To date, the captive breeding program has gone remarkably well. More than 120 eggs have been produced by the two captive females. These eggs have been collected and are currently being incubated. Some eggs have recently hatched and more are expected to hatch as this article goes to press.

Aptly, the first hatching occurred on a day that was both Threatened Species Day and Fathers Day. The young stick-insects are miniature replicas of the adult, except they are bright green in colour, not dark chocolate-brown like their parents.

Meanwhile, planning is underway to eradicate rats from Lord Howe Island. The Foundation has given $33,000 towards a cost-benefit analysis of rat eradication, including the steps that will be needed to protect the woodhen and other species during the baiting programme. The money is also being used to research quarantine procedures that will prevent the introduction of other alien species.

It is hoped that the removal of rats will allow the Lord Howe Island Phasmid to be reintroduced to the island, where it can once again claim its rightful place as the heavyweight of the island’s vast menagerie of unique and remarkable insects.

Dr David Priddel is a senior research scientist with the Department of Environment and Conservation (New South Wales National Parks and Wildlife Service) specialising in seabird conservation, island ecology and the recovery of threatened fauna.

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