Dryococelus australis, also known as the Lord Howe Island stick insect, Lord Howe Island phasmid or, locally, as the tree lobster, is a species of stick insect that lives in the Lord Howe Island Group. It is the only member of the monotypic genus Dryococelus. Thought to be extinct by 1920, it was rediscovered in 2001. Although it had been extirpated from Lord Howe itself, a remnant population of 24 individuals was rediscovered on the sea stack of Ball's Pyramid. The species has been called "the rarest insect in the world".

Adult Lord Howe Island stick insects can measure up to 20 centimetres (8 in) in length and weigh 25 grams (1 oz), with males 25% smaller than females. They are oblong in shape and have sturdy legs. Males have thicker thighs than females. Unlike most phasmida, the insects have no wings.

The behaviour of this stick insect is highly unusual for an insect species, in that the males and females form a bond in some pairs. 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 quality has allowed the species to survive when they are low in numbers.

The stick insects were once very common on Lord Howe Island, where they were used as bait in fishing. They were believed to have become extinct soon after the supply ship SS Makambo ran aground on the island in 1918, allowing black rats to become established. After 1920, no stick insects could be found. The species was declared extinct.

In 1964, a team of climbers visiting Ball's Pyramid, a rocky sea stack 23 kilometres (14 mi) south-east of Lord Howe, discovered a dead stick insect. In subsequent years, climbers found a few more fresh carcasses, but expeditions to find live specimens were unsuccessful.

In 2001, Australian scientists David Priddel and Nicholas Carlile hypothesised that there was sufficient vegetation on the islet to support a population of the insects, and, with two assistants, travelled there to investigate further. They scaled 120 metres of grassy, low-angled slope, but found only crickets. On their descent, the team discovered large insect droppings under a single Melaleuca shrub growing in a crevice approximately 100 metres 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, scrambled back up the slopes. They discovered a small population of 24 insects living beneath the Melaleuca shrub amongst a substantial build-up of plant debris.

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.