Animal Fact Sheets
Lord Howe Island Stick Insect (Dryococelus australis)
The Lord Howe Island Stick Insect was listed as presumed extinct in the IUCN Red List and is now listed as endangered under Schedule 1 of the NSW Threatened Species Conservation Act 1995.
The adults measure up to 15 cm long, weigh up to 25 g and are a glossy black colour. Neither sex can fly. Unlike other stick insects that hang upside down and move slowly, the Lord Howe Island Stick Insects can walk and even run along the ground. The females have strong hooks on their legs and have a thicker, heavier body than the males.
Their large size has given the Lord Howe Island Stick Insect the nickname of ‘land lobsters’.
The Lord Howe Island Stick Insect was thought to be extinct for the past 80 years. It was rediscovered by a ranger who was rock climbing on Ball’s Pyramid in February 2001.
Staff from Melbourne Zoo’s Invertebrate Department travelled to Lord Howe Island with rangers from the NSW National Parks and Wildlife and collected four stick insects from the known population of seventeen. One pair came to Melbourne Zoo and one pair travelled to Sydney. At Melbourne Zoo, the first egg hatched on Threatened Species Day – September 7th 2003.
Each egg is weighed, measured and housed individually to ensure as much information is collected as possible.
At Melbourne Zoo, the Lord Howe Island Stick Insects are held in a temperature and humidity controlled glasshouse, as close as possible to those on Lord Howe Island.
Breeding and Lifecycle
On average, a male will mate with a female once or twice through the night. On average, a female will lay up to 300 eggs in her lifetime. Some pairs consistently sleep together with the male’s legs around the female, while other pairs do not.
Most stick insects remain in their tree and let their eggs fall to the ground. However the female Lord Howe Island Stick Insect climbs down to the ground and pushes her abdomen into the soil to lay her eggs. The oval shaped eggs are about 4 mm long. She lays in batches of nine, resting for about ten days between batches. The eggs incubate under the soil for about six and a half months before hatching.
Newly hatched young are a bright green colour and active during the day. When disturbed, they display the camouflaging behaviour of swaying like a small leaf in the wind. As the young mature, they progress from green, through brown to black through successive moults, as they become increasingly active at night.
Habitat and distribution
The only known habitat of the Lord Howe Island Stick Insect is Ball’s Pyramid, 700kms north-east of Sydney and 23kms south-east of Lord Howe Island. At 548 m tall, Ball’s Pyramid is the world’s tallest and most isolated rocky sea-stack, with sheer cliffs rising straight out of the sea.
Diet
The only vegetation growing on Ball’s Pyramid is a species of melaleuca, Melaleuca howeana, so plants grown from the same seed stock are used at Melbourne Zoo to feed the insects. Banyan trees, Ficus macrophylla columnaris, also grow on Lord Howe Island so ten species have been trialled successfully with the insects as an alternative food source at Melbourne Zoo.
Threats to Survival
These stick insects were once common on Lord Howe Island and would shelter in Banyan trees during the day, emerging at night to feed. Tragically, a supply ship, the Mokambo, ran aground there in 1918, releasing rats onto the island. Along with five species of birds, the Lord Howe Island Stick Insect had disappeared by 1930.
It is thought that either seabirds carried several stick insects over to Ball’s Pyramid or that they were carried by floating vegetation from the main island. There the stick insects shelter in rocky crevices through the day and feed on the melaleuca at night.
In order to return the species to Lord Howe Island, a systematic rat eradication program would have to be implemented and successful.
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