Mono Lake diving beetle: missing for 100 years—and sought in the wrong place

A mistake with consequences

For a long time, the case seemed clear: the Mono Lake diving beetle lived—so it was assumed—in Mono Lake in California’s Sierra Nevada. A lake that could hardly be more inhospitable: highly alkaline, extremely saline, and with conditions to which only a few specialized organisms can adapt.

But that was precisely where the beetle was never found again. For decades, researchers searched for the species in Mono Lake—without success. The American entomologist Russell D. Anderson wrote in 1983:

“I have collected in alkaline Mono Lake and studied collections made by numerous other workers in the area, but I have seen no other examples of this species.”

Two years later he went even further and declared that the Mono Lake diving beetle was “known exclusively from the alkaline waters of Mono Lake.” However, he cites no source for this assumption. Even so, this assessment shaped the image of the species for decades—and contributed to it being classified by the IUCN from 1986 onward as “extinct?” and later, from 1996 onward, as “extinct.”

In fact, the story begins quite differently. When the entomologist Henry Clinton Fall first formally described the species in 1919, he had only a single male specimen before him. A small animal, slenderly built, with yellowish-brown coloration and finely punctate elytra. It was collected on June 12, 1917, presumably by Frank Ellsworth Blaisdell, whose name Fall gives as the source of the type material. It remains unclear whether Blaisdell collected the specimen himself or whether it came from his collection.

What is striking, however, is less what Fall describes than what he does not mention: He does not say a word about the beetle living in Mono Lake. In the original description, he names only “Mono County, California” as the locality. And yet that later became the accepted idea.

Why this misconception arose can no longer be fully reconstructed today. A central role was probably played by the work of Russell D. Anderson. He assumed that the beetle lived in Mono Lake and searched specifically in its alkaline waters—without success. This interpretation was subsequently adopted by other works and shaped perceptions of the species for decades.

This idea may also have been reinforced by the later common English name Mono Lake diving beetle. In the scientific literature, the assumption gradually became entrenched—and with it the search in the wrong place.

The Mono Lake diving beetle belongs to the family of diving beetles (Dytiscidae), of which around 3,200 species have been described worldwide. Diving beetles breathe air, which they take in at the water surface and store under their elytra. Many larger species therefore have to surface regularly, while smaller species can also remain underwater for longer periods. With a body length of only around three millimeters, the Mono Lake diving beetle is among the smaller representatives of this group.

Mono Lake diving beetle – fact sheet

alternative name	Mono Lake hygrotus diving beetle
scientific names	Hygrotus artus, Leptolambus artus, Coelambus artus
range	Freshwater habitats in the surroundings of Mono Lake (California, USA)
time of extinction	after 1917 — rediscovered in 2017!
causes of extinction	unclear
IUCN status	extinct

The crucial clue—and the search in the right place

For decades, the Mono Lake diving beetle was known exclusively from a single specimen, the holotype collected in 1917. Only about a century later, during investigations of the genus Hygrotus, the entomologists Gil Challet and Hans Fery noticed a detail that had long been overlooked.

Besides the well-known label “Mono Co., Cal.” (Mono County, California), the holotype bears another inscribed “Farrington, Mono Lake”—presumably added in Blaisdell’s own handwriting. This label had previously been ignored both by Anderson and by other authors.

The trail led to a crucial insight: “Farrington” refers to the former Farrington Ranch, which in the late 19th and early 20th centuries lay around five kilometers from Mono Lake. This produced a completely new picture: the beetle had very probably never been found in the lake itself, but rather in its surroundings.

Challet and Fery drew the obvious conclusion from this—and fundamentally changed the search strategy. Instead of continuing to look for the missing beetle in the highly alkaline Mono Lake, they focused on the surrounding freshwater habitats: small streams, ponds, and other non-alkaline bodies of water in the region.

Several attempts were initially unsuccessful, but in August 2017—exactly 100 years after the species was discovered—the breakthrough finally came: about 700 meters south of the remains of Farrington Ranch, they found five specimens of Hygrotus artus. The Mono Lake diving beetle had been rediscovered.

The results published in 2020 confirmed not only the identity of the species, but also a central insight: The beetle does not live in Mono Lake itself, but in the non-alkaline waters of its surroundings. It had never vanished—people had simply been searching in the wrong place.

Challet and Fery also note that the Mono Lake diving beetle is “fairly widespread in Mono County (California).”

The Mono Lake diving beetle—a Lazarus species

That the Mono Lake diving beetle was long considered missing or extinct is less a biological problem than an epistemological one. Once an assumption had become established—that the beetle lived in Mono Lake—it was no longer questioned for decades. It determined where people looked, and thus also what could be found at all.

The case shows exemplarily how easily such misconceptions can take on a life of their own—and what consequences that can have. If a species is prematurely declared extinct, conservation measures are often discontinued. In conservation biology, this is referred to as the Romeo and Juliet effect, named after Shakespeare’s tragedy, in which a false assumption about death ultimately leads to catastrophe in the first place. Applied to species conservation, this means: A species is given up because it is considered lost—and that can be exactly what causes it to be truly lost.

The Mono Lake diving beetle is therefore not an example of final extinction, but of a so-called Lazarus species—a species that was long thought missing and later rediscovered. Such cases show how important it is to examine data critically, take historical sources seriously, and keep questioning even seemingly secure assumptions.

Taxonomy: From Coelambus to Hygrotus

The taxonomic classification of the Mono Lake diving beetle was refined in the course of new systematic studies. Henry Clinton Fall originally described the species in 1919 as Coelambus artus. Today it is listed as Hygrotus (Leptolambus) artus.

This is based on a comprehensive revision of the diving beetle tribe Hygrotini by Ignacio Ribera Villastrigo and his team (2017), based on molecular and morphological data. The study showed that several previously used genera did not represent natural kinship groups. As a result, the systematics were reorganized: Coelambus was integrated into the genus Hygrotus, and a differentiated subgenus concept was introduced with Leptolambus.

Today, the Mono Lake diving beetle, Hygrotus artus, is regarded as a clearly delimited, independent species. Earlier suggestions that it might be identical with species such as Hygrotus sharpi or Hygrotus fumatus had already been disproved by examination of the holotype: Anderson demonstrated clear differences in genital morphology. The rediscovery by Challet and Fery (2020) also confirmed its species status.

Hygrotus artus was therefore never a taxonomic phantom or a vanished species, but a real species that was simply misunderstood for a long time. Other diving beetles regarded as extinct, however, have probably in fact disappeared forever, including the New Guinea diving beetle (Rhantus papuanus), the Brazilian diving beetle, and Perrin’s cave beetle from France.

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Sources

• Anderson, R. D. (1983). Revision of the Nearctic species of Hygrotus groups IV, V and VI (Coleoptera: Dytiscidae). Annals of the Entomological Society of America 76(2), 173–196.
• Anderson, R. D. (1985). Proposed faunal affinities of the Great Basin Dytiscidae (Coleoptera). Proceedings of the Academy of Natural Sciences of Philadelphia 137(1), 12–21.
• Anonymous (2020). A register of extinct beetles. Latissimus 45, 26–28.
• Challet, G., & Fery, H. (2020). Rediscovery of Hygrotus (Leptolambus) artus (Fall, 1919), description of Hygrotus (L.) yellowstone nov. sp. and notes on other species of the genus (Coleoptera, Dytiscidae, Hydroporinae, Hygrotini). Linzer biologische Beiträge, 52(1), 37–79.
• Fall, H. C. (1919). The North American species of Coelambus. John D. Sherman, Jr.
• Villastrigo, A., Ribera, I., Manuel, M., Millán, A., & Fery, H. (2017). A new classification of the tribe Hygrotini Portevin, 1929 (Coleoptera: Dytiscidae: Hydroporinae). Zootaxa 4317(3), 499–529. https://doi.org/10.11646/zootaxa.4317.3.4
• World Conservation Monitoring Centre. 1996. Hygrotus artus. The IUCN Red List of Threatened Species 1996: e.T10345A3195883. https://dx.doi.org/10.2305/IUCN.UK.1996.RLTS.T10345A3195883.en