Charles Darwin had kind of a thing for beetles, and would go to great lengths to collect and study them. In 1846, he wrote to a friend about one of the entomological adventures he had looking for ground beetles:
Under a piece of bark I found two Carabi & caught one in each hand, when lo and behold I saw a sacred Panagæus crux major; I could not bear to give up either of my Carabi, & to lose Panagæus was out of the question, so that in despair I gently seized one of the carabi between my teeth, when to my unspeakable disgust & pain the little inconsiderate beast squirted his acid down my throat & I lost both Carabi & Panagæus!
During his famous voyage on the Beagle in the 1830s, Darwin collected fossils and living animals for his research wherever he could, including plenty of beetles. Among them was a type of rove beetle—a member of Staphylinidae, the largest beetle family—that was unknown to science.
Unfortunately, before Darwin—who apparently could not bear to lose a beetle—or any other biologist could formally describe the new beetle and name it, the specimen was misplaced somewhere in the collections of the Natural History Museum in London.
Skip ahead almost 200 years, to the present day. Stylianos Chatzimanolis, an entomologist at the University of Tennessee, has been working over the last few years to update the family tree of a sub-group of rove beetles. He’s spent many hours in his lab examining specimens borrowed from all over the world and working on manuscripts (while listening to David Sedaris audiobooks). One day, he noticed that one of the beetles had notched antennae, a trait that’s not common among rove beetles. Intrigued, he looked into it a little more and discovered that the strange beetle was on loan from the Natural History Museum, and was the lost beetle collected by Darwin in Argentina.
The beetle was recorded as specimen number 708 by Darwin in his notes, and then stored at the museum among unsorted Staphylinidae specimens, presumably because no one knew what it was or where it belonged. Eventually one of the curators noticed it while sorting these materials and, taking a best guess, moved it to storage with the genus Trigonopselaphus, to which it bore a resemblance. This happened to be the same genus that Chatzimanolis was researching, and when the museum sent over its Trigonopselaphus collections, specimen 708 made a second trip over the Atlantic, this time to be rediscovered instead of lost.
After examining the beetle more closely, Chatzimanolis decided that it wasn’t a member of Trigonopselaphus, but a new genus. He dubbed the group Darwinilus in honor of Darwin, and named specimen 708’s species D. sedarisi as a nod to the writer who entertained him while he worked. He published his description of the beetle on Darwin’s 205th birthday, February 12, 2014.
Despite searching in many major museum collections, Chatzimanolis has only been able to find one other specimen of Darwinilus sedarisi, which dates from 1935 or before. Chatzimanolis thinks the lack of specimens may be because the beetles spend most of their time hiding and feeding in the trash piles of ant colonies. Most of the area around the spots where the two beetles were found, though, has since been deforested and turned into farmland, so it's also possible the beetles disappeared for lack of a place to live. “One of course hopes that a newly described species is not already extinct,” says Chatzimanolis.