The Return of the Stick Insect
How a creature that was considered extinct for many decades was found on a rocky Pacific island and saved for the world.
Now it was not a spectacularly beautiful insect, and not one we cannot live without. But its disappearance and subsequent rediscovery holds lessons for biodiversity, species interaction and conservation.
I have always been fascinated by stick insects, which I encountered on my travels in South and Middle America, and in Asia — where in southern Indian Tamil they were called “stick pūcci”. It was not that they were particularly attractive, but they were mostly so difficult to see.
I kept searching for them and marveling at the camouflage they use to avoid predators. And the very frugal body mass that makes it hardly worthwhile to hunt for them for food.
Unless you are a stick insect on a Pacific island, a Dryococelus australis, also known colloquially as the “tree lobster,” due to its size and glossy exoskeleton. It measured over 10 centimeters in length and weighed up to 25 grams. Dryococelus was the largest flightless stick insect in the world.
These creatures lived on Lord Howe Island, a small, lush volcanic remnant landmass jutting off the east coast of Australia. They were used as bait in fishing — until 1920, when they suddenly disappeared completely from the island.
What had happened?
In 1918 the supply ship SS Makambo ran aground on the island, and some black rats escaped. These invasive predators feasted on the succulent “tree lobsters,” rapidly decimating them, until two years later no stick insects could be found on the Island. They had been particularly vulnerable to rat predation because they were flightless, nocturnal and slow-moving. From 1920 on the species was considered extinct.
Now for the good news, which quite inexplicably fills me with relief. In 1960, climbers on another nearby volcanic rock island, Ball’s Pyramid, found the remnants of what appeared to be the “extinct” Dryococelus australis. And in 2001, when researchers returned to Ball’s Pyramid, they found a few living examples. Several of the insects were collected and taken to Melbourne, where they were placed in a captive breeding program.
However, scientists were not certain that the insects they were breeding were the same as the ones that had gone extinct a century earlier. They had darker brown bodies, and thinner back legs than the museum specimens from Lord Howe Island.
But then DNA sequencing was conducted on the museum specimens and the captive-bred stick insects, and it was discovered that there was less than one percent genetic variance —which was enough to classify them as belonging to the same species. A paper entitled “Museum Genomics Confirms that the Lord Howe Island Stick Insect Survived Extinction” was published in the journal Current Biology.
In the above illustration from that paper, museum specimens from Lord Howe Island are shown on the left, and captive-reared specimens originally from Ball’s Pyramid are shown on the right. It is unclear whether these are species-level differences or merely environmental variations.
So what about the rats that had escaped from the grounded vessel and encountered an ecological paradise, with slow-moving, flightless, stick insects that became easy prey to the voracious rodents. A Lord Howe Island Rodent Eradication Project (REP) was implemented to eradicate rats and mice from the island. A 100-day operation distributed poison baits across all parts of the island group. After that intensive surveillance was implemented to detect any remaining rodents, and when breeding rats were found, in 2021, a rapid eradication response was activated, which included the use of detection dogs.
In October 2023, after a two-year monitoring period, Lord Howe Island was declared free of rats and mice. This paves the way for the reintroduction of Dryococelus australis to its ancestral home. Hurrah!
