How come cockroaches, which have been "extinct" for more than 80 years, reappeared? !

Speaking of cockroaches, it probably brings back painful memories for many people.

Whenever you see a cockroach suddenly jump out and then disappear from your sight, your blood pressure will probably jump up, and then you will complain: Why can't these cockroaches be completely eliminated?

For cockroaches, which are one of the "four pests", people just want them not to appear in front of them, but not all cockroaches will break into our homes, mess up the environment, and spread diseases. Some cockroach species play an important role in the ecosystem.

The Lord Howe Island wood-eating cockroach (Panesthia lata) is one of these.

Lord Howe Island wood-eating cockroach. Image source: Wikipedia

01

Once spread across Lord Howe Islands

But after the arrival of humans, it is hard to find any traces

In the southwestern Pacific Ocean, there is an isolated oceanic archipelago called the Lord Howe Islands. Formed by volcanic eruptions, the Lord Howe Islands are famous for their large number of rare plant and animal species.

Lord Howe Islands and surrounding islands. Image source: References

The Lord Howe Island wood-eating cockroach is one of the original inhabitants of the archipelago.

As a large, wingless wood-eating cockroach unique to the island, the Lord Howe Island wood-eating cockroach was once distributed throughout the island, playing a very important role in maintaining the island's ecosystem.

Specifically, male Lord Howe Island wood-eating cockroaches are typically 33-40 mm long, have a metallic sheen, a red to black head and body, and red legs, while females are 32.5-41 mm long, are typically darker than males, and lack the males' metallic sheen.

The Lord Howe Island wood-eating cockroaches do not look like the "bullies" of cockroaches in our homes, but more like a darker "enlarged version" of pill bugs. They look larger and move slowly, and because they have no wings, they have lost the ability to fly.

Wood-eating cockroaches on Lord Howe Island. Image source: sydney.edu.au

Of course, what everyone is most concerned about may be whether they will "break into private homes."

The answer is of course no.

As the name suggests, the Lord Howe Island wood-eating cockroach feeds on wood and the forest is its home. They do not enter people's houses, but only recycle wood and fallen leaves in the forest to keep the forest healthy. In addition, they may be a source of food for some birds on the island.

Unfortunately, not much is known about the Lord Howe Island wood-eating cockroach.

In 1868, biologist Walker discovered and described this peculiar species. In 1887, Australian naturalists landed on Lord Howe Island and conducted a comprehensive scientific survey. They saw traces of wood-eating cockroaches on a rotten log and recorded them.

But before any in-depth study could be conducted, this "big guy" of a cockroach had disappeared from the island.

The reason why this cockroach is almost extinct is actually rat infestation!

02

Stowaway rats

It is the cockroach's "unexpected" enemy

In 1918, a ship ran aground on Lord Howe Island and black rats (Rattus rattus) on board came to the island by accident.

Within a few years of the black rats' arrival, five species of forest birds endemic to Lord Howe Island had become extinct, and at least 13 species of invertebrates have since disappeared, including the Lord Howe Island wood-eating cockroach.

Black rat. Image source: wikipedia

Despite numerous searches, the Lord Howe Island wood-eating cockroach seemed to have disappeared from the islands after specimens were collected in the 1830s, and it is generally believed that the Lord Howe Island wood-eating cockroach probably ceased to exist on the main island of the Lord Howe Islands 80 years ago.

According to relevant reports, there were more than 300,000 rats living on the island at one time. They were rampant on Lord Howe Island, damaging crops, preying on invertebrates, eating bird eggs...

Finally, in 2019, a $15 million rodent eradication program was launched to remove the destructive invasive species, namely those nasty rats. The program was carried out from May to November 2019 after 15 years of detailed research and planning.

The rat eradication operation has played a positive role in the recovery of endangered wildlife on the island. After the eradication, local people heard the long-lost sound of crickets again, and the number of some endangered birds also showed an upward trend.

So, people began to think about getting the Lord Howe Island wood-eating cockroach back on the island.

Some people may ask, aren’t these cockroaches eaten by mice?

In fact, the wood-eating cockroaches on Lord Howe Island have not been extinct. On small islands other than the main island, these cockroaches still exist in areas that have not been occupied by black rats.

Scientists discovered traces of these "big guys" on Ball's Pyramid Island, 23 kilometers south of Lord Howe Island. In addition, they were also found on several small islands near the main island.

But the latest findings suggest the cockroaches may never have truly disappeared from Lord Howe Island.

03

Reunion after more than 80 years

Wood-eating cockroaches return to Lord Howe Island

The extinction of the wood-eating cockroaches on Lord Howe Island was caused by an accidental stranding, and the scientists' rediscovery of these "big guys" on the island was also due to an accident.

In 2001, wood-eating cockroaches were also found on two small islands near Lord Howe Island, Blackburn Island and Roach Island. Twenty years later, scientists from the University of Sydney were scheduled to go to Blackburn Island to investigate and study the local wood-eating cockroaches.

However, a bout of bad weather prevented them from travelling to Blackburn Island, so they decided to check potential sites on Lord Howe Island, which had been infested with wood-eating cockroaches before the rats arrived.

They reached a grove of banyan trees on the northern side of Lord Howe Island, where they turned over a rock.

Then, something amazing happened! There was a small colony of wood-eating cockroaches under the stone!

Image source: sydney.edu.au

Scientists studied the wood-eating cockroaches that were rediscovered on the island and the results showed that the population on the main island is genetically different from the populations found on Blackburn Island and Roach Island, which means that they are likely to be the "indigenous survivors" of the island. More research is still underway.

For scientific researchers, rediscovering the wood-eating cockroach is undoubtedly exciting, but for the wood-eating cockroach, being discovered itself may not be something to be excited about.

And if they weren't endangered, who would care about a group of cockroaches under a rock?

References:

[1] 'Extinct' wood-eating cockroach rediscovered after 80 years.

https://www.sydney.edu.au/news-opinion/news/2022/10/01/extinct-wood-eating-cockroach-rediscovered-after-80-years.html

[2] A large cockroach thought extinct since the 1930s was just rediscovered on a small island in Australia

https://theconversation.com/a-large-cockroach-thought-extinct-since-the-1930s-was-just-rediscovered-on-a-small-island-in-australia-191847

[3] Carlile, N., Priddel, D., & O'Dwyer, T. (2018). Preliminary surveys of the endangered Lord Howe Island cockroach Panesthia lata (Blattodea: Blaberidae) on two islands within the Lord Howe Group, Australia. Austral Entomology, 57(2), 207-213.

[4] Maekawa, K., Matsumoto, T., & Nalepa, CA (2008). Social biology of the wood-feeding cockroach genus Salganea (Dictyoptera, Blaberidae, Panesthiinae): did ovoviviparity prevent the evolution of eusociality in the lineage?. Insectes Sociaux, 55(2), 107-114.

[5] Rodent Eradication Project

https://lhiroenteradicationproject.org/the-project/

Produced by | Science Popularization China

Author: EVEE (School of Life Sciences, Peking University)

Producer｜China Science Expo

Submitted by: Computer Information Network Center, Chinese Academy of Sciences