New beetle species with unique trait discovered on island

Australian researchers recently discovered a previously unknown species of scarab beetle (Scarabaeidae) in the insect collection of the Australian Museum in Sydney. The specimen in question, a female, was collected on January 30, 1979 on Lord Howe, a small island of only 14 square kilometers in the southwest Pacific. The species was endemic exclusively to the rainy cloud forest on the summit of Mount Gower at elevations of 700 to 875 meters. The newly discovered species, Semanopterus kingstoni, is the sixth species of this genus known from Lord Howe Island.

Flightless beetle supports Darwin’s island theory on the loss of flight in insects

What is special about Semanopterus kingstoni is its inability to fly—a trait that is extremely rare in rhinoceros beetles (Dynastinae), a subfamily of scarab beetles. In the original description, published in the journal Zootaxa, entomologist Chris Reid of the Australian Museum emphasizes that this new scarab beetle species may be the only oceanic and flightless species. This supports Charles Darwin’s theory about the loss of flight in insects on islands, similar to what is known from birds that evolved from flight-capable relatives and forgot how to fly over the course of evolution.

Many flightless bird species evolved especially on oceanic islands because flight brought them more disadvantages than advantages. Birds that could not fly. Numerous flightless bird species once lived on Lord Howe Island, including the Lord Howe swamphen, which was exterminated between 1790 and 1834 through intensive hunting.

In contrast to birds, where the loss of flight on islands is often due to evolutionary adaptations, Darwin argued that the loss of flight in beetles has different causes. Flying insects on islands risk being blown out to open sea by the wind, which is why insects that stay on the ground are more likely to survive.

Only one specimen known: new scarab beetle species probably already extinct

The inability to fly only became a disadvantage when humans settled the islands. The discovery of Lord Howe Island in 1788 marked the start of human presence, and from the 1860s onward mice and later rats reached the island, with devastating effects on the native fauna. Despite these challenges, the island is still considered relatively ecologically intact.

Beetles on Lord Howe have been studied and described since the early 1850s, with the estimated number of species at 535, only a small percentage of which were introduced through human activities. In the last 50 years, scientists have intensively surveyed Lord Howe Island for macroinvertebrates, including beetles. For his study, Reid spent nine nights searching for beetles on the summit and lower slopes of Mount Gower, but found no specimens of the flightless scarab beetle species S. kingstoni.

Because the species has not been recorded since 1979 and because of its inability to fly, the study assumes that it is probably already extinct. Nevertheless, there remains a glimmer of hope of rediscovering the species, because the Lord Howe Island cockroach, considered missing since the 1930s, was found again on the island last year. If, however, S. kingstoni should indeed prove to be extinct, possible causes could include the destruction or fragmentation of its habitat as well as increased risk from predators such as ground-dwelling birds or small mammals.