Darwin’s Rove Beetle

A chance find gave it its own name

On August 24, 1832, the HMS Beagle anchored in Bahía Blanca Province in eastern Argentina. On board the ship: the then 23-year-old British naturalist Charles Darwin. During the voyage he collected rock samples, plants, marine animals and a great many beetles. He sent the collected specimens, some preserved in conservation fluid, back home to Cambridge.

Between September 6 and October 17, 1832, Darwin discovered an unusually large rove beetle (Staphylinidae) with a long, segmented body and a blue-green gleaming head on the coast of Bahía Blanca. He once again sent this remarkable beetle, together with numerous fossil animal finds from a nearby bay, to England.

Only 180 years after Darwin had collected the beetle in Argentina, as Christopher Kemp writes in The Lost Species (2019), entomologist Stelios Chatzimanolis found the animal again in 2012. During a reassessment of the genus Trigonopselaphus, a small group of rove beetles, he requested undetermined material of the genus from the National History Museum in London. He then received a box with 24 beetles pinned on needles—one of them was Darwin’s rove beetle, which had evidently been assigned to the wrong genus.

Chatzimanolis immediately saw that one beetle was in no way similar to the others: it was larger, its head was blue-green instead of dark brown or black, and its antennae were serrated like a saw, a characteristic that hardly any other animal species and certainly no rove beetle displays in this form.

Darwin’s rove beetle – fact sheet

scientific name	Darwinilus sedarisi
original range	Argentina
time of extinction	unclear, between 1832 and 1935
causes of extinction	possibly habitat loss

Where did inventory number 708 spend almost two centuries?

Darwin’s rove beetle was lost among countless insects in a huge collection built up over centuries. Once an insect is misassigned as one among millions of specimens, the chances of ever finding that exact animal again drop to almost zero.

As late as 1987, the male beetle to which Darwin had once given inventory number 708 was listed as missing in the article Darwin’s Insects: Charles Darwin’s Entomolocial Notes, which insect researcher Alexei Solodovnikov, however, was unwilling to accept. He began searching for the missing beetle and in fact found it in 2008 in unsorted Staphylinidae material at the London museum. By mistake, however, Solodovnikov then placed the specimen among further unsorted beetles of the genus Trigonopselaphus, where Chatzimanolis finally rediscovered it by chance four years later.

In February 2014, Chatzimanolis gave the unusual beetle its name: Darwinilus sedarisi, honoring both Darwin and the U.S. writer David Sedaris, to whose audiobooks Chatzimanolis listened while composing the first description of the insect for the journal ZooKeys.

Because it is customary and more reliable to describe a new species not from just one specimen, Chatzimanolis searched for further rove beetles like the one Darwin had once found in Argentina. He was fortunate: he discovered a paratype, which he could describe alongside the holotype, in the Museum für Naturkunde in Berlin. The male specimen was damaged and came from a collector named Breuer, who had collected the beetle at the Río Cuarto in the Argentine province of Córdoba, nearly 800 kilometers north of Bahía Blanca.

Because the German entomologist Walther Horn mentions the beetle in one of his books published in 1935, Breuer must have captured the animal before 1935. Beyond that, nothing is known about the circumstances of how and when the beetle reached the Berlin museum.

Darwin’s rove beetle: missing or extinct?

Today nobody can say with certainty whether Darwin’s rove beetle is simply missing or whether it is already extinct. What is fairly certain is that no one who knows beetles and could recognize it as unusual has seen it in the last 100 years. It cannot be ruled out that it follows a hidden way of life, because some related species also live concealed and inhabit ant nests or nests of other hymenopterans (Hymenoptera).

It appears just as likely that the rather large rove beetle is extinct, because humans have transformed a large part of the area between the two collection sites Bahía Blanca and Río Cuarto: the forests were cleared and converted into farmland. Chatzimanolis himself tried to find further specimens of these rove beetles in other collections, unfortunately without success. He tends to assume that the species is extinct, since its type locality has disappeared. This assumption becomes all the more likely the smaller the species’ original range was.

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