Lord Howe Island is a Unesco World Heritage site, between mainland Australia and the North Island, and is home to many unique species. Photo: 123rf
When a University of Sydney biology student lifted a rock under a huge banyan fig tree on Lord Howe Island, he could hardly believe what he saw.
It was a wingless wood-eating cockroach, unique to one tiny World Heritage-listed island that lies between Sydney and the North Island, and believed to be extinct.
It was last seen more than 80 years ago.
"For the first 10 seconds or so, I thought, 'No, it can't be,'" honours student Maxim Adams said.
"We were doing a brief survey of Lord Howe basically to confirm its extinction there … and lo and behold the first rock we looked under there it was. It was really unbelievable."
The wood-feeding cockroach (Panesthia lata) was once widespread across the Lord Howe Islands archipelago, but was believed to have become extinct after rats arrived in 1918.
Searches had previously discovered similar closely related cockroaches on two even smaller islands in the archipeligo, but the cockroaches Adams rediscovered are genetically different from those.
The "extinct" wood-eating cockroach rediscovered on Lord Howe Island. Photo: Supplied/ University of Sydney - Justin Gilligan/ Australian Department of Planning and Environment
Research takes unexpected turn
Adams is a student under University of Sydney evolutionary biologist Nathan Lo.
Professor Lo has been leading a research team examining the population distribution of cockroaches across the archipelago.
He said a major rodent eradication program on Lord Howe Island in 2019 had been so successful that his team were investigating the possibility of introducing a population of the other different cockroaches from the outer islands onto the main island.
Adams and Department of Planning and Environment scientist Nicholas Carlile had gone to Lord Howe Island ahead of Professor Lo to make a start, when their research took a very unexpected turn.
"They were due to go out to Blackburn Island to start studying the cockroaches there, the weather was really bad, so they were forced to stay on Lord Howe Island," Professor Lo said.
Maxim Adams under the banyan tree where he rediscovered the Lord Howe Island cockroach. Photo: Supplied/ University of Sydney - Nicholas Carlile/Australian Department of Planning and Environment
"They went for a walk to the north end to look at some of the habitat where ... cockroaches might have been happy to stay.
"The very first rock they looked under they found cockroaches, which is very strange, as entomologists have been looking on the island for many decades and haven't seen any at all."
The researchers ended up finding families of the cockroaches, all under one banyan tree.
The cockroach plays a role as an "ecosystem engineer" on Lord Howe Island. Photo: Supplied/ University of Sydney - Justin Gilligan/ Australian Department of Planning and Environment
Genetically distinct
Professor Lo said DNA work had confirmed the importance of the discovery.
"We sequenced their DNA and compared it with the DNA of cockroaches from Blackburn and so far, they seem different. The same species probably, but they seem to be a distinct population," he said.
"It does seem this little population in the north end of the island has hung on over many decades. It's exciting, they might be able to re-establish across the island over time."
Lord Howe Island board chair Atticus Fleming said it was an exciting find.
"Lord Howe Island really is a spectacular place. It's older than the Galápagos Islands and is home to 1600 native invertebrate species, half of which are found nowhere else in the world," he said.
"These cockroaches are almost like our very own version of Darwin's finches, separated on little islands over thousands or millions of years developing their own unique genetics."
'Charismatic' cockroach ecologically important
Professor Lo said the native wood-eating cockroaches played an important environmental role.
"They are incredibly important nutrient recyclers, ecosystem engineers and as a food source for other species," Professor Lo said.
He said the species also deserved a better rap than "common street roaches".
"It doesn't smell, it doesn't run really quickly, it's not scary. It's actually quite charismatic, you can hold it in your hand," he said.
"It just hangs out in the forest. It does not go into people's houses. It's just out in the forest recycling the wood and leaf litter, to keep the forest healthy.
"That's why we are interested in it, because it was so abundant before the rats wiped it out. We figure it was probably playing a pretty important ecological role on the island, also acting as food for a number of the bird and reptile species out there."
Professor Lo said there was still much to learn.
"This species lives for a long time, about seven or eight years, but doesn't breed anywhere as quickly as your common street roaches," he said.
"We are hoping to study their habitat, behaviours and genetics to learn more about how they managed to survive."
-ABC
