The eastern Palearctic carabid beetle Synuchus congruus (Morawitz, 1862) is recorded from Belarus, Latvia, and Poland. Images of habitus, morphological features, and aedeagi, as well as an updated key to the Synuchus species of Europe, are provided.

Carabid beetle, Europe, identification key, new records

The genus Synuchus Gyllenhal, 1810, a member of the family Carabidae, includes 86 species found in the Palearctic, Oriental, and Nearctic regions (Bousquet 2012; Hovorka 2017; Kurian and Thomas 2022). The species diversity in the genus is unevenly distributed across its range, with the vast majority of species known from East Asia, particularly in Japan, Russian Far East, China, and the Korean Peninsula. Until now, only one species—Synuchus vivalis (Illiger, 1798)—was known to inhabit Europe. It occurs from the Iberian Peninsula, France and the British Isles in the west, Israel and Turkey in the south, through Central and Northern Europe, European Russia, the Caucasus, Siberia, and Central Asia to the Russian Far East, north-east China, and Japan (Hovorka 2017), where it can be found mainly in open habitats (Koch 1989; Lindroth 1992; Magura et al. 2000; Aleksandrowicz 2014) from lowlands to rather high elevations in mountains.

The present paper provides data on the surprising presence of Synuchus congruus (Morawitz, 1862) in Central and Eastern Europe. Considering its probable widespread distribution in the region, we provide diagnostic characters and an updated key for the identification of Synuchus species of Europe.

The study is based on specimens collected during various field trips in Belarus, Poland, and Latvia over the last several years. In addition, all available Synuchus specimens preserved in a number of institutional and private collections in the listed countries were examined for the presence of S. congruus. The collections referred to in this study are abbreviated as follows:

SPCM Scientific and Practical Center of the National Academy of Sciences of Belarus for Biological Resources, Minsk, Belarus

DUBC Daugavpils University, Institute of Life Sciences and Technology, Daugavpils, Latvia

PUIB Pomeranian University in Słupsk, Institute of Biology, Słupsk, Poland

FRI Forest Research Institute, Białowieża, Poland

cKuz collection of V. Kuznetzov, Minsk, Belarus

An updated key to European Synuchus species was prepared on the basis of a morphological study of collected beetles and existing keys (Lindroth 1956; Lafer 1989). The distributional map was made using SimpleMappr (Shorthouse 2010). Photographs of the beetles and their aedeagi were made using a Canon EoS 6D digital camera with a Canon MP-E 65 mm macro lens, StackShot system and helicon Focus auto montage. Final post-processing of images was done in Adobe Photoshop.

Synuchus congruus was originally described as Taphria congrua by Morawitz (1862) from the “Bureja-Gebirge” (Bureinsky Ridge near Amur River, Russian Far East). In 1893, Tschitschérine described Synuchus latus from the Zabaykalsky Krai, Russia. Habu (1955) recognized that the two forms were conspecific and proposed their synonymy, which was consistent with the views of Lindroth (1956). The previously known range of the species includes Russia (southern Kuril Islands, southern Sakhalin, Primorskii Krai, southern Khabarovskii Krai, Jewish Autonomous Region, Amurskaya Oblast’, Transbaikalia, southern Siberia, southern Ural), Kazakhstan, North and South Korea, Japan, and the northwestern, northern, and northeastern regions of China (Šustek 2003; Sundukov and Makarov 2013; Saimova et al. 2020; Zhu 2022).

New data show that S. congruus has spread across Eastern and Central Europe. It has been recorded from Słupsk in the west to Minsk in the east, from Latvia in the north to Brest Polesie in the south-western Belarus. Although ground beetles have been one of the most active areas in beetle research in Europe over the past decades, what is most surprising is that it was overlooked in the region for many years and probably confused with S. vivalis, since the two species are extremely similar in habitus. In fact, a careful study of the carabids stored in the collections of the SPCM and PUIB showed that several specimens belonging to this species were initially misidentified as S. vivalis.

The earliest detected specimen of S. congruus from the studied collections was sampled in northern Poland in 2007. This suggests that the species was introduced into Europe prior to that year, although the exact time and point of entry are unlikely to be accurately determined. The study of beetles preserved in other collections, primarily those sampled from Poland, Germany, the Baltic countries, and the northwestern part of European Russia, could provide valuable insights. The method of introduction is also unknown, but may be due to the importation of plant stock or associated materials, as is known for other alien ground beetle species, such as Pterostichus vagus in Czech Republic (Hůrka and Šustek 1995) (previously recognized as P. caspius until its revision by Muilwijk et al. 2024), Leistus fulvibarbis in Norway (Westergaard et al. 2015), and multiple cases from North America (Kavanaugh and Erwin 1985; Spence and Spence 1988; Kavanaugh and LaBonte 2008). The ability for active flight allowed S. congruus to spread further in Europe.

In its native range, S. congruus is found in coniferous and deciduous forests, as well as on forest edges, clearings, bush thickets, and meadows, along riverbanks, and in wetlands (Lafer 1976; Sundukov 2009; Rogatnykh 2009; Shabalin et al. 2010; Sundukov and Makarov 2013; Sundukov 2024). In our study, the species was collected both in forest and open habitats of varying degrees of naturalness: from old-growth oak and hornbeam forests in Białowieża Forest and semi-natural oak-dominated forests to municipal woodlands, fallow fields and wooded strips surrounded by agricultural lands. It was observed from spring to late autumn. In several localities, the species was collected together with S. vivalis.

Future studies will help to accumulate data on the distribution of S. congruus in Europe, especially in neighboring countries (Germany, Ukraine, Lithuania, Estonia, and the European part of Russia) and to clarify its habitat and ecological preferences.

We thank Prof. Jerzy Gutowski (Białowieza, Poland) and Vladislav Kuznetzov (Minsk, Belarus) for providing additional material, Dr Alexey Tishechkin (Sacramento, USA) for the correction of the English text, and anonymous reviewers for suggestions.