Tobias’ caddisfly: Germany’s only endemic species to have gone extinct

Inconspicuous, highly specialised insects

Caddisflies are among those insects that hardly anyone notices. They are inconspicuous, quiet and do not impose themselves on people. In 2002, the Austrian entomologist Hans Malicky described them aptly as animals that “cause neither harm nor any particular benefit”, that “do not sting and do not bite”, and that “only exceptionally stray into human dwellings”. They “simply exist”—as “many small cogs in nature’s household”.

This inconspicuousness likely contributed substantially to the fact that Tobias’ caddisfly also remained largely unknown. As an unassuming species with no immediate relevance to humans, its decline never entered public awareness. Yet caddisflies have high ecological requirements and react sensitively to deteriorations in water quality. The disappearance of Tobias’ caddisfly went unnoticed—long before its absence was even registered.

The IUCN has listed the Tobias’ caddisflyas extinct since 1983. It is thus the only species endemic to Germany that is officially considered to have gone extinct in modern times. All other species listed as extinct in Germany—as well as worldwide—also occurred in other countries, including the Aurochs, the Chiem whitefish (Coregonus hoferi), the Starnberg whitefish (C. renke) and the Lake Constance whitefish.

Tobias’ caddisfly – fact sheet

alternative name	Tobias’ caddis-fly
scientific name	Hydropsyche tobiasi
native range	Rhine-Main region, Germany
time of extinction	after 1938
causes of extinction	Environmental pollution (water pollution)
IUCN status	extinct

Discovery and first scientific description

The German entomologist Wolfgang Tobias first studied in more detail the caddisfly that would later bear his name as early as 1972 . At that time, however, it was still assigned to other species. Only five years later did Hans Malicky recognise that several specimens from the Rhine region labelled as Hydropsyche exocellata represented a previously unrecognised species . Malicky formally described it in 1977 as Hydropsyche tobiasi.

In his paper, Malicky notes that the specieshad been misidentified for decades—mostly because of its external similarity to H. exocellata. Only a detailed examination of the male genital structures made it possible to clearly distinguish it and recognise it as a separate species.

The original description was based solely on male specimens; females and larvae could not be assigned with certainty. The holotype and paratypes come from the Rhine area, which early on already suggested a very narrow distribution range .

In a renewed review of historic collection material, Wolfgang Tobias and Peter J. Neu evaluated in a 2004 study additional voucher specimens: two males from Rüdesheim, one male from Assmannshausen and a specimen that had been caught in a light trap on 4 August 1938 near Klingenberg on the Main. This individual represents the last confirmed record of Tobias’ caddisfly.

An endemic of the Middle Rhine and the Main

Tobias’ caddisfly is known exclusively from eight localities along the Rhine and the Main:
– Assmannshausen
– between Biebrich and Assmannshausen (1906)
– confluence of the Sieg (1908)
– Königswinter (1909)
– Rüdesheim (1913)
– Neuenahr (1914)
– Bonn (1914)
– near Klingenberg on the Main (1938).

All known records of the species come from the Rhine-Main region. Accordingly, Tobias and Neu assign the occurrence of Tobias’ caddisfly to the Middle Rhine—among others near Rüdesheim, Assmannshausen and Königswinter—as well as to the Main near Klingenberg; added to this is a record at the confluence of the Sieg. All documented occurrences lay on the Rhine terraces between Bonn and Mainz and on a short stretch of the Main near Klingenberg.

There are no records outside this area. Malicky (2014) therefore assumes that Tobias’ caddisfly was probably an endemic of the Middle Rhine and the Main.

Despite targeted and intensive searches at the known localities—for example in 1979 near Oppenheim, Wiesbaden-Schierstein and Ingelheim, and in 2003 and 2004 near St. Goarshausen and Kaub—the species could not be rediscovered.

A river-dweller with exacting requirements

“The species place high demands on their habitats. Only a few tolerate water pollution. Most depend on clean waters and a good oxygen supply in the water. (…) Thus, they are excellent indicators (…) not only of the health of the water body, but also of intact structures within a stretch of river.”

What Hans Malicky describes here in general for caddisflies (Trichoptera) applies to Tobias’ caddisfly in particular. Its disappearance can be directly linked to the long-term deterioration of water quality in large rivers—especially the Rhine and the Main, the only known habitats of the species.

The Rhine and the Main as polluted rivers

The pollution of the Rhine began as early as the industrialisation of the 19th century. From the second half of the century onwards, the burden increased sharply and reached its peak between the 1920s and the 1960s. For decades, the Rhine was one of the most polluted rivers in Europe. A comparable development also took place on the Main, which as an important tributary was particularly strongly affected by urban and industrial discharges.

Several factors acted together: municipal wastewater was for a long time discharged into the Rhine and Main without treatment. Along both rivers, industrial centres also concentrated—including chemical, metal, paper and pulp industries—whose wastewater often contained toxic substances . Oxygen deficiency, pollutant inputs and contaminated sediments led in many stretches to a massive decline of sensitive aquatic organisms.

In parallel with the chemical burden, both rivers were profoundly reshaped. Straightening, embankment works and canalisation, as well as the loss of side arms and gravel banks, destroyed fast-flowing microhabitats, structurally diverse substrates and refuges. Above all, specialised species are affected by such changes—possibly including Tobias’ caddisfly.

Extinct before restoration

In a study published in 2004 on the Hydropsychidae occurring in Germany—a caddisfly family with net-spinning larvae in running waters—Tobias and Neu conclude that Tobias’ caddisfly became extinct after the Second World War as a result of the wastewater pollution of the Rhine and Main that lasted for more than 30 years. Before the war, especially between about 1906 and the 1920s, the species, by contrast, had still been observed relatively frequently.

At the same time, the authors point out that Tobias’ caddisfly may have been rare even earlier—a circumstance that likely further increased its vulnerability to the rapidly emerging environmental changes.

Malicky (2014) also emphasises that the Rhine and Main were so heavily polluted in the 20th century that almost all caddisfly species in these river systems disappeared for a time. Many species were able to recover as water quality improved, but Tobias’ caddisfly remained permanently missing. As a regionally endemic species, presumably strictly tied to large rivers, it was likely already completely gone before restoration measures began. The species that returned either had remnant populations in tributaries or refugia, or had a high dispersal ability.

The ecological restoration of the Rhine and the Main did begin institutionally around 1950, but only showed measurable success from the 1970s onwards—among other things through the expansion of wastewater treatment plants, bans on particularly harmful substances and international agreements such as the work of the International Commission for the Protection of the Rhine (IKSR). For Tobias’ caddisfly, last recorded in 1938, this development came too late.

A particularly threatened habitat type

In Tobias and Neu’s assessment, Tobias’ caddisfly was a potamal species, specialised on the lower reaches of larger rivers. In addition to several caddisfly species, typical animals of this habitat include beavers, otters and sand martins. Potamal species are considered particularly sensitive to environmental change, as they depend on stable conditions in large river systems and respond sensitively to pollution, loss of structure and river regulation. Accordingly, many potamal species are now among the most threatened—or have already disappeared.

A species known only from collections

Very little is known about Tobias’ caddisfly. The preserved museum specimens are still the only direct evidence of its existence. There are no observations of living individuals, and larvae of this species could never be collected or reliably assigned. Accordingly, many aspects of its way of life remain in the dark.

The known specimens are now held in historical collections. The holotype as well as most of the paratypes are kept at the Zoological Museum Hamburg. Additional voucher specimens are held at the Senckenberg Museum Frankfurt and in the Entomological Collection of ETH Zurich. All known specimens were collected between about 1906 and 1938; there are no more recent records.

From the descriptions by Tobias and Neu it follows that the insects had a dark brown body, while legs and hindwings were somewhat lighter. The forewings were uniformly coloured and reached a length of up to 13 millimetres, placing the species among the smaller representatives of the caddisflies.

Besides Tobias’ caddisfly, around 19 other caddisfly species are considered probably extinct worldwide, including many regional endemics, especially from the United States and the Canary Islands.

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Sources

• Malicky, H. (1977). Ein Beitrag zur Kenntnis der Hydropsyche guttata-Gruppe (Trichoptera, Hydropsychidae). Zeitschrift der Arbeitsgemeinschaft Österreichischer Entomologen, 29. 1–28.
• Malicky, H. (2002). Die Frauenfeld-Köcherfliege (Platyphylax frauenfeldi): Porträt eines fast ausgestorbenen Insekts. ÖKO·L, 24(3), 29–34.
• Malicky, H. (2014). Hydropsyche tobiasi. The IUCN Red List of Threatened Species 2014: e.T10332A21426347. https://dx.doi.org/10.2305/IUCN.UK.2014-1.RLTS.T10332A21426347.en
• Neu, P. J., & Tobias, W. (2004): Die Bestimmung der in Deutschland vorkommenden Hydropsychidae (Insecta: Trichoptera). Lauterbornia, 51. 1–68.