The white objects on the wingcases are grains of sand.

The designation fuscus means brown, dark. The first impression however is a light brown or beige waterbeetle with a somewhat greenish tinge. The underside of the beetle in fact is black-brown. The namesakes probably thought this was a striking feature, compared to the light underside of many other water predatory beetles. In addition, the pronotum has a dark brown spot. The dark underside is clearly visible in the photo below. The beetle in the second photo is a specimen of Rhantus suturalis, a beetle that is somewhat smaller than the brown duiker, but otherwise very similar. Both beetles are common, but do not have an English name.

Colymbetes fuscus

Rhantus suturalis

The Brown Diver is common everywhere, yet I only found it after years. This specimen was in a small pool among dense masses of algae and aquatic plants. With its flat and smooth body, it can quickly dart away. Maybe that's why he's usually too fast for a landing net. This time I used an applesauce sieve, which is easier to pull through bunches of water plants, and suddenly there was this nervously crawling and jumping beetle in it.

The beetles of the genera Colymbetes and Rhantus are classified in the Colymbetinae a subfamily of the large family Dytiscidae (diving beetles). For comparison, here on the same scale a Rhantus suturalis caught in the same pool. Both species appear to have beige elytra, but when viewed up close, the base color is yellow-brown, with dense black markings on top. In Colymbetes the pattern is a network of black, transverse grooves, while in Rhantus it is black coils.

Colymbetes fuscus - Rhantus suturalis

Colymbetes fuscus - Rhantus suturalis

Other genera within the Colymbetinae are Agabus and Ilybius. These are nearly all black beetles. Agabus bipustulatis is very common in Europe.

The underside of Colymbetes fuscus stands out darkly against the light yellow protruding elytra (epipleura). Click on the image to see some detailed shots.his is a male specimen, recognizable by the widened front and middle legs with adhesive discs, which are important for mating (see: Blunck, 1912).

front leg - middle leg

Colymbus in the Century Dictionary

What's in a name?

The designations brown and fuscus have already been discussed at the beginning of this page. The scientific name of the beetle was Dytiscus fuscus Linnaeus 1758, so: Linnaeus named the beetle that way in 1785 and it means something like: 'the dark diver'. Many water predatory beetles were called Dytiscus and there was a need for clearer systematics. In 1806, the Swiss entomologist de Clairville proposed a 'new method', introducing the name Colymbetes.The name was accepted and the beetle was then named Colymbetes fuscus (Linnaeus 1758), i.e. with brackets, according to the rules of the ICZN.

What exactly Colymbetes means was not so easy to find. On bugguide.net I found the Century dictionary from 1907 as a tip (see Literature). The picture above on the left shows the explanatory piece from that dictionary. Here you can read that Colymbus means diver, so the translation of the beetle name remains the same: 'dark diver'. See also: Wikipedia - κολγμβοσ and Wikipedia - Columba.

Literature:

Blunck, H. jan 1912 Kleine Beiträge zur Kenntnis des Geschlechtslebens und der Metamorphose der Dytisciden. 1. Teil. Colymbetes fuscus L. und Agabus undulatus Schrank.Zoologischer Anzeiger 41 2. 534-546
Retrieved March 24, 2024 from: https://www.zobodat.at/pdf/ZoologischerAnzeiger_41_0534-0546.pdf

Clairville,J. 1806 Helvetische Entomologie, oder, Verzeichniss der schweizerischen Insekten nach einer neuen Methode geordnet : mit Beschreibungen und Abbildungen by SchellenbergJohann Rudolf, 1740-1806; Thompson, J. Christian, former owner. DSI Publication date 1798 Topics Insects Publisher Zürich : Bei Orell, Füssli und Compagnie Collection biodiversity; americana Contributor Smithsonian Libraries Language German; French Volume v.2 (1806) Parallel t.p.: "Entomologie helvétique, ou, Catalogue des insectes de la Suisse." Text in German and French (PAGINA's: 198-201)
DOI: https://doi.org/10.5962/bhl.title.15822
Read March 24, 2024 at: https://archive.org/details/helvetischeentom02sche/page/190/mode/2up

The Century dictionary : an encyclopedic lexicon of the English language: prepared under the superintendence of William Dwight Whitney 4 Car-Con Whitney, William Dwight, 1827-1894
Read March 24, 2024 at: https://www.biodiversitylibrary.org/item/217268#page/304/mode/1up

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