Northward range extension of Atrichops crassipes (Meigen, 1820) (Diptera, Athericidae) in the Baltic ecoregion, with the first record from Latvia

the journal of biodiversity data NOTES ON GEOGRAPHIC DISTRIBUTION 1138 Academic editor: Maíra Araújo Received: 6 October 2025 Accepted: 6 November 2025 Published: 24 November 2025 Copyright © The authors. This is an open‑access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0) Abstract. The first record of Atrichops crassipes (Meigen, 1920) (Diptera, Athericidae) in Latvia is reported, to‑ gether with additional findings from Lithuanian waters in 2015. The data are based on larval records collected during freshwater macroinvertebrate research and water‑quality monitoring. Atrichops crassipes represents a new Diptera species record for Latvia and marks the northernmost limit of the species known range. Our data suggest that A. crassipes is expanding its range northward, possibly driven by climate warming. Key words. Aquatic insect, larval observations, Least Water‑snipefly, new localities Ozoliņš D, Jēkabsone J, Piterāns U, Višinskienė G, Arbačiauskas K (2025) Northward range extension of Atrichops crassipes (Meigen, 1820) (Diptera, Athericidae) in the Baltic ecoregion, with the first record from Latvia. Check List 21 (6): 1138–1142. https://doi.org/10.15560/21.6.1138 INTRODUCTION The family Athericidae comprises 10 genera worldwide (Nagatomi and Stuckenberg 2004), of which four genera are reported from Europe (Lablat 2023). The genus Atrichops Verall, 1909 globally contains 11 extant species (Muller et al. 2023), with the least water‑snipefly Atrichops crassipes (Meigen, 1820) being the only rep‑ resentative of the genus in Europe (Schmidt‑Kloiber and Hering 2025). In general, A. crassipes is considered a Western and Central European species with findings from the United Kingdom, Belgium, the Netherlands, Spain, France, Germany, Italy, the Czech Republic, Poland, Slovakia, and Romania (Murányi et al. 2009). Ac‑ cording to the International Union for Conservation of Nature (IUCN) criteria, A. crassipes has been assessed as Vulnerable in the Czech Republic (Kolaříková et al. 2014), but as Endangered in Poland (Głowaciński et al. 2002). In the last two decades, this species has been reported for the first time from several European coun‑ tries: Hungary (Murányi et al. 2009), Switzerland (Sartori et al. 2011), and Portugal (Andrade 2014). The life cycle of A. crassipes is reported to be biennial, with the adult flight period occurring from mid‑ June to August (Gerke and Böttger 2001). Ecological studies suggest that A. crassipes is a thermophilic spe‑ cies (Daufresne et al. 2003; Bulánková et al. 2019) that prefers lower altitudes (Sartori et al. 2011). The larvae are strictly aquatic, preying on other aquatic invertebrates, such as chironomids and oligochaetes, and typically inhabit soft substrates in streams, rivers, and standing waters. Adult females are haematophagous and have been reported to feed on frogs (Thomas 1997). In Lithuania and Latvia, only two species of Athericidae belonging to the genus Atherix Meigen, 1803 are listed in published checklists of Diptera (Pakalniškis et al. 2006; Karpa 2008). However, some larval observa‑ tions of A. crassipes from Lithuania have been previously mentioned in ecological studies (Bernotienė and Višinskienė 2007, 2008). Our study reports the first and northernmost occurrence of A. crassipes in Latvia, documents new localities in Lithuania, and reviews the species known distribution. METHODS The specimens in Latvia were collected in the Tartaks River during the national surface water monitoring programme conducted by the Latvian Environment, Geology and Meteorology Centre (LEGMC). The Tartaks is a medium‑sized rheophilic river with a catchment area of 890 km². Altogether 77% of the landcover in the 21 (6) · https://doi.org/10.15560/21.6.1138 21 (6): 1138–1142. https://doi.org/10.15560/21.6.1138 Northward range extension of Atrichops crassipes (Meigen, 1820) (Diptera, Athericidae) in the Baltic ecoregion, with the first record from Latvia Dāvis Ozoliņš1,2, Jolanta Jēkabsone2, Uģis Piterāns3, Giedrė Višinskienė4, Kęstutis Arbačiauskas4 1 Institute of Biology, Faculty of Medicine and Life Sciences, University of Latvia, Riga, Latvia 2 Latvian Environment, Geology and Meteorology Centre, Riga, Latvia 3 Zoology Department, Latvian National Museum of Natural History, Riga, Latvia 4 State Scientific Research Institute Nature Research Centre, Vilnius, Lithuania Corresponding author: Dāvis Ozoliņš ([email protected]) Check List 21 (6) · https://doi.org/10.15560/21.6.1138 Ozoliņš et al. · Atrichops crassipes in the Baltics 1139 Tartaks River catchment area consists of agricultural land, while 23% are covered by forests. The sampling was done on 25 April 2023. Five replicate kick‑samples were collected near the riverbank using a standard hand net from dominating substrates at depths ranging from 0.3 to 0.6 m. The riverbed was covered by sand and silt, with emergent macrophytes (Glyceria fluitans(L.) R.Br., Phalaris arundinacea L., and Sparganium emersum Rehmann) growing along the banks, and a moderate amount of woody debris was present (Figure 1). The material from Latvia is deposited in the voucher specimen collection of LEGMC, Rīga, and two spec‑ imens are deposited in the collection of the Latvian National Museum of Natural History (LNMNH), Rīga. The records from Lithuania were obtained from the publications of Bernotienė and Višinskienė (2007, 2008), the doctoral dissertation of Višinskienė (2010) and unpublished data collected by the Laboratory of Evolutionary Ecology of Hydrobionts at the Nature Research Centre (NRC). The new material of A. crassipes from Lithuania presented in this study were collected in the larval stage in 2015 and deposited in NRC, Vilnius. Information on the global distribution of Atrichops crassipes (Meigen, 1920) was obtained from the Glob‑ al Biodiversity Information Facility (GBIF 2025) and published literature (Murányi et al. 2009; Sartori et al. 2011; Andrade 2014; Zeegers and Pollet 2024). The distribution map was made using ArcMapv. 10.8.2 (Esri 2011). RESULTS Family Athericidae Atrichops crassipes (Meigen, 1820) New records. LATVIA — AugšdAugAvA MunicipAlity • Višķu parish, Tartaks River; 56°04’44”N,026°49’01”E; 103 m alt.; 25.IV.2023; K. Paulauska leg.; 1 larva mounted on plastic card, LNMNH, En Dip/5651, 1 larva in ethanol, LNMNH, En Dip/5652, 5 larvae in ethanol, LEGMC, 23ZB0031/AC LITHUANIA — druskininkAi MunicipAlity • Merkys River near the road to Druskininkai; 54°08’39”N, 024°12’18”E; 73 m alt.; 30.IX.2015; K. Arbačiauskas leg.; 1 larva in ethanol, NRC, NRCE000251 — lAzdijAi district MunicipAlity • Baltoji Ančia River near Kapčiamiestis; 53°59’08”N,023°39’29”E; 108 m alt.; 30.IX.2015; K. Arbači‑ auskas leg.; 2 larvae in ethanol, NRC, NRCE000252 — pAnevėžys district MunicipAlity • Nevėžis River near Liū‑ dine; 55°41’06”N, 024°27’55”E; 41 m alt.; 28.IX.2015; K. Arbačiauskas leg.; 5 larvae in ethanol, NRC, NRCE000250 • Nevėžis River near Panėvežys, near the Sanžilė Canal; 55°44’07”N, 024°14’09”E; 28 m alt.; 28.IX.2015; K. Ar‑ bačiauskas leg.; 4 larvae in ethanol, NRC, NRCE000249 — švenčionys district MunicipAlity • Žeimena River below Pabradė wastewater treatment plant; 54°57’57”N, 025°43’43”E; 117 m alt.; 24.IX.2015; K. Arbačiauskas leg.; 2 larvae in ethanol; NRC, NRCE000253 • Žeimena River at Kaltanėnai; 55°15’10”N, 025°59’29”E; 141 m alt.; 24.IX.2015; K. Arbačiauskas leg.; 2 larvae in ethanol, NRC, NRCE000255 • Žeimena River at Liūlinė; 55°06’04”N, 025°56’52”E; 133 m alt.; 24.IX.2015; K. Arbačiauskas leg.; 5 larvae in ethanol, NRC, NRCE000254 Figure 1. The habitat of Atrichops crassipes in Tartaks River, Latvia (14.VI.2025). Check List 21 (6) · https://doi.org/10.15560/21.6.1138 Ozoliņš et al. · Atrichops crassipes in the Baltics 1140 Distribution. The known distribution of A. crassipes based on literature and the localities of our study is shown in Figure 2. Identification. The morphology of the larvae is very distinctive and cannot be confused with that of other Diptera species. The larvae have prolegs on abdominal segments 1–7. Abdominal segments 6 and 7 each bear four tracheal projections (two dorsal and two lateral), and two additional projections are present on the anal segment. The tracheal projections are at least half the length of the body. Last‑instar larvae mea‑ sure 14–15 mm in length (Thomas 1997; Figure 3). DISCUSSION The checklist of Latvian Diptera includes 1,654 confirmed species, although the estimated total is around 3,600 species (Karpa 2008). In comparison, the Lithuanian dipteran fauna includes 3,311 species (Pakalniškis et al. 2006). Both works mention two species belonging to the family Athericidae: Atherix aurichalcea Becker, 1921 and A. ibis (Fabricius, 1798) (Pakalnišķis et al. 2006; Karpa 2008). In Lithuania, all identified athericid spec‑ imens were in the adult stage: eight A. aurichalcea females were recorded (Dumčius and Pakalniškis 2004), along with one A. ibis male (Podėnas and Pakalniškis 2000). It is noteworthy that Atrichops crassipes is absent from the Lithuanian Diptera checklist, despite frequent occurrences of its larvae in benthic invertebrate surveys (Bernotienė and Višinskienė 2007, 2008; Višinskienė 2010; unpublished data from the Laboratory of Evolutionary Ecology of Hydrobionts, NRC). Since the Lithuanian Diptera checklist is based solely on adult specimens, A. crassipes has remained unreported in the published records of the Lithuanian fauna. In differ‑ ent studies of Lithuanian river macroinvertebrates, it was found that A. crassipes was a common species in medium‑sized rivers (Bernotienė and Višinskienė 2007). Studies in the Lithuanian rivers Neris and Šventoji Figure 2. The geographical distribution of Atrichops crassipes. red dots = occurrences in Latvia and Lithuania; yellow dots: occurrences elsewhere in Europe (GBIF 2025). Figure 3. The larva of Atrichops crassipes (Meigen, 1821), collected in Višķu parish, Tartaks River, 25.IV.2023. Check List 21 (6) · https://doi.org/10.15560/21.6.1138 Ozoliņš et al. · Atrichops crassipes in the Baltics 1141 have revealed a positive relationship not only between river current velocity and total aquatic invertebrate abundance, but also between current velocity and A. crassipes larval density (Bernotienė and Višinskienė 2008). We suggest that A. crassipes is a new species for Latvia as the surface water monitoring program has been active since 2006 and encompasses the entire territory of the country (LEGMC 2009). In contrast, A. crassipes was first recorded in Lithuania in 2003 and has since been regularly detected in benthic inverte‑ brate samples. Based on our 2023 finding in Latvia, we assume that the species is a recent addition to the Latvian fauna, rather than a result of insufficient sampling efforts in the past. The biennial life cycle of A. crassipes confirms that the larvae are present in water throughout the year (Gerke and Böttger 2001). Our results suggest that A. crassipes is undergoing a range extension northwards, as it was previously considered a species of Western and Central Europe (Sartori et al. 2011; Bulánková et al. 2019). The locality in Latvia rep‑ resents the northernmost known limit of the species, which had previously been recorded only as far north as the United Kingdom (GBIF 2025). The mean annual temperatures are known to be increasing in the Baltic countries (Jaagus etal. 2014; Kalvāns et al. 2023) and Sartori et al. (2011) mentioned A. crassipes as a potential climate migrant, as it appears to benefit from climate warming (Daufresne et al. 2003; Bulánková et al. 2019). The low altitudes of the Baltic ecoregion (Jusik et al. 2015) seems to correspond to the favorable habitat requirements of this species (Sartori et al. 2011). In conclusion, we suggest that A. crassipes will expand its distribution across Latvian waters in the coming decades and continue to spread northwards. ACKNOWLEDGEMENTS We thank all the participants of Latvian freshwater macroinvertebrate monitoring programme for fieldwork, and Dr. Dmitry Telnov (Natural History Museum: London) for comments on the insect collections. We also gratefully acknowledge the anonymous reviewers. ADDITIONAL INFORMATION Conflict of interest The authors declare that no competing interests exist. Ethical statement No ethical statement is reported. Funding This research received no external funding. Author contributions Conceptualization: DO. Data curation: DO, GV, KA. Investigation: DO, JJ, GV. Methodology: DO, JJ, UP, GV, KA. Supervision: DO, GV. Visualization: JJ, UP. Writing – original draft: DO, GV. Writing – review and editing: DO, JJ, UP, GV, KA. Author ORCID iDs Dāvis Ozoliņš https://orcid.org/0000‑0003‑3752‑2040 KęstutisArbačiauskas https://orcid.org/0000‑0001‑8688‑2291 Data availability All data that support the findings of this study are available in the main text. Data from the specimens collected in this study are deposited in GBIF via the Pensoft IPT and available at the following link: https:// doi.org/10.15468/e5b7wp. 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