Invertebrates
Lord Howe Island Stick Insect
Dryococelus australis · also called lord howe island stick insect, tree lobster, land lobster
The Lord Howe Island stick insect is one of the rarest insects on Earth and the subject of one of conservation’s most improbable comeback stories. A hand-sized, flightless, glossy-black phasmid once so common on its island that people used it for fish bait, it was eaten to extinction by shipwreck rats — and then, 80 years later, found alive on the side of a sea stack, clinging to a single bush.
Overview
The species is native to Lord Howe Island, in the Tasman Sea. It is one of the heaviest stick insects in the world, 12–15 cm long and up to 25 g, with a thick dark body, stout legs, and no working wings. It eats the leaves of shrubs and small trees.
Extinction by rat
Black rats came ashore from the grounded steamer Makambo in 1918, and within a few years the large, slow, ground-sheltering insect had vanished from the island. By around 1960 it was presumed globally extinct.
Rediscovery
In 2001, a population later counted at about 24 adults was found living under a single Melaleuca bush on a ledge of Ball’s Pyramid, a sheer 562 m spire 23 km away. In 2003 two breeding pairs were taken into captivity; one female, “Eve,” nearly died and was nursed back with a hand-mixed calcium-and-nectar slurry.
Bred back
Melbourne Zoo and other institutions have since reared many thousands. Keepers found that pairs roost together at night, the male draping his legs over the female. A major rodent eradication on Lord Howe Island, completed in 2019, has opened the way for the insect to be returned home.
Status
The Lord Howe Island stick insect is Critically Endangered. The only wild population is the tiny one on Ball’s Pyramid; the species otherwise survives as a managed captive population descended from very few founders.
Lord Howe Island Stick Insect: common questions
How did the Lord Howe Island stick insect survive on Ball's Pyramid?
Ball's Pyramid is a bare, near-vertical volcanic spire with very little soil or vegetation, and for decades it was assumed to hold nothing that could support a large insect. In fact a single patch of the shrub Melaleuca howeana had taken root in a crack on a ledge a hundred metres or so above the sea, fed by a seep of water, and a small colony of the stick insects was living in the leaf litter and moist debris beneath it. Climbers had reported dead insects and droppings on the rock as early as the 1960s, but it was not until a 2001 expedition specifically searched at night that living animals were found.
Who were Adam and Eve?
They were the two adult pairs, and especially one pair, taken off Ball's Pyramid in 2003 to start a captive-breeding programme. Shortly after arriving at Melbourne Zoo the female, Eve, became gravely ill and stopped moving. The keeper caring for her, Patrick Honan, improvised a treatment of ground-up calcium and nectar fed drop by drop, and she recovered and went on to lay eggs. Because so few founders were available, the modern captive population is descended from a very small number of individuals, which is a long-term genetic concern.
Why did the species go extinct on Lord Howe Island in the first place?
The cause was the arrival of the black rat. When the supply ship Makambo ran aground at Lord Howe in 1918, rats got ashore and spread across the island. The stick insect was large, slow, flightless, and spent the day hidden in cavities and leaf litter on or near the ground, which made it easy prey. Within about two years islanders noted that the once-common insects had gone, and the same rats went on to drive several of Lord Howe's endemic birds to extinction as well.
Will the stick insect be returned to Lord Howe Island?
That is the goal. The single biggest obstacle, the introduced rodents, was removed by a major eradication campaign declared successful in 2019. With the island rat-free, captive-bred stick insects can in principle be released back into suitable habitat, and trial reintroductions and habitat preparation have been planned. It is a slow, carefully monitored process, because managers want to be sure the island is genuinely and permanently rodent-free and that the released insects establish a self-sustaining wild population.