Stick insect survived extinction by hiding out

In June 1918, a ship called SS Makambo ran aground on Lord Howe Island, 600 kilometres east of the Australian mainland, and unleashed an ecological disaster.

Black rats aboard the ship quickly colonised the island, which harboured no native mammals, nor any kind of carnivorous species capable of eating the rodents. Within a very short period, five bird and 13 insect species had vanished.

Among the casualties was a stick insect (Dryococelus australis) thought to be endemic only to the island. After decades of fruitless searching by entomologists, the species was declared extinct in the 1960s.

The declaration, it turns out, was premature. In 2001, some intrepid climbers discovered a handful of stick insects in the top of a tree on a nearby mid-ocean rocky outcrop called Ball’s Pyramid. They looked similar, but not identical, to museum specimens of the Lord Howe Island species.

Entomologists revisiting the uninhabited rock the following year found 24 specimens, and took some to establish a captive breeding program at Melbourne Zoo, back in Australia.

And now, in very welcome news, scientists at the Okinawa Institute of Science and Technology in Japan have used genetic sequencing to confirm that, despite their outward differences, the Ball’s Pyramid insects are definitely the same species as the extinct Lord How Island ones.

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The two insects look different morphologically, which raised questions about whether they were the same species.
Credit: You Ning Su / CSIRO

The two insects are noticeably different, with visibly divergent structures on their hind legs. However, their DNA diverges by less than 1%, a range narrow enough for them to be declared the same species.

The discovery, and the ongoing success of the captive breeding program, means that in time Lord Howe Island will once again host its unique species.

“In this case, it seems like we’re lucky and we have not lost this species forever, although by all rights we should have,” says lead researcher Alexander Mikheyev. “We get another chance – but very often we do not.”

Island locals and relevant authorities are keen to see the stick insect reintroduced to the island. Before that can happen, however, there is still one major obstacle to be overcome: the eradication of the rats.

The research is published in the journal Current Biology.

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