Bembidiini (Coleoptera, Carabidae, Trechinae) is one of the most species-rich tribes of ground beetles in the Iberian Peninsula and Balearic Islands. In this territory, Bembidiini represents about 10% of the carabid fauna, with 130 species belonging to the genera Bembidion Latreille, 1802 (108 spp.), Asaphidion Gozis, 1886 (9 spp.), Ocys Stephens, 1828 (5 spp.), Cillenus Samouelle, 1819 (1 sp.) and Sinechostictus Motschulsky, 1864 (7 spp.) (Ortuño & Toribio, 2005; Serrano, 2020). The carabid beetles of this tribe are common elements of humid habitats, such as river and lake shores, in where they generally prey on other invertebrates (Andersen, 1970; Hering & Plachter, 1997).

The genus Ocys is a well-defined group that occupies a basal position in the phylogeny of Bembidiini (Maddison, 2012). It is characterized by a labium fused with the pre-basilar, a careniform apical striola and the presence of an only one discal setigerous pore (Ortuño & Toribio, 2005). In the Iberian Peninsula and Balearic Islands, some Ocys are endemisms with a narrow distribution and strict habitat requirements, others are euryoic ground beetles easily found in so many humid habitats and others are poorly known species that have been collected very sporadically in the territory (Ortuño & Toribio, 2005). In particular, the last two different situations occur between two close related species of the Ocys s. str. group: Ocys harpaloides (Audinet-Serville, 1821) and Ocys tachysoides (Antoine, 1933).

Ocys harpaloides is a widespread Palearctic element (Marggi et al., 2003: 272) and the most common species of Ocys in the Iberian Peninsula and Balearic Islands (Ortuño & Toribio, 2005). Abundant data of O. harpaloides have been provided from this region (Baehr, 1986; Zaballos, 1989; Andújar et al., 2000; Novoa et al., 2003; Ortuño & Toribio, 2005; Peláez & Salgado, 2007; Serrano et al., 2015; Toribio & Ramos Abuín, 2018; among others).

On the other hand, O. tachysoides is a rare species in the territory (4 records; Sciaky, 1998; Toribio, 2013; Toribio & Ramos Abuín, 2018). It was described as a “form” of O. harpaloides occurring in North Africa (Antoine, 1933), but afterwards the same author raised it to the category of species (Antoine, 1955). The decision was based principally on differences in elytra shape and aedeagus morphology, and the typical expressions of these characters were described for the two Ocys (Antoine, 1955). The first record of O. tachysoides in the Iberian Peninsula was provided by Sciaky (1998) from Portugal, and the existing scarce data were summarized in the monography of Iberian Bembidiini published by Ortuño & Toribio (2005). Since then, only some comments and three more records were published (Toribio, 2013; Toribio & Ramos Abuín, 2018), so the knowledge about Iberian populations of this species has been hardly increased.

More recently, Maddison & Anderson (2016) played an integrative morphological and molecular study on specimens from North Africa and different regions of Europe (including the Iberian Peninsula) that confirmed the validity of the taxonomic status of O. tachysoides. Maddison & Anderson (2016) also demonstrated that several European collection samples of O. tachysoides have been wrong identified as “forms” of O. harpaloides, so its global distribution was largely increased. In addition, Maddison & Anderson (2016) proposed new diagnostic characters and described their typical expression in both species: elytra coloration, spermatheca morphology, microsculpture pattern and shape of the hind angles of pronotum.

Soon after the publication of the work of Maddison & Anderson (2016), new wrong-identified collection material of O. tachysoides was detected in Germany and the Netherlands, increasing again the chorological knowledge of the species (Fritze et al., 2017; Muilwijk & Felix, 2017). However, Muilwijk & Felix (2017) suggested that some of the morphological external characters reported by Maddison & Anderson (2016) were similar between some Dutch samples of O. harpaloides and O. tachysoides, so not all of them would be completely reliable for the species identification.

We hypothesized that the scarce number of records of O. tachysoides in the Iberian Peninsula may results from the difficult distinction of the two species of Ocys, especially before the publication of the most recent works. To test this hypothesis, we re-studied Iberian collection material of O. harpaloides and Ocys sp. in order to detect wrong and/or non-identified individuals of O. tachysoides. In addition, we assessed the species recognition based on external characters in this material and in three recently collected individuals of O. tachysoides. The objectives of the present study are: 1) provide new records of O. tachysoides in the Iberian Peninsula; 2) study the consistency of the diagnostic external characters of O. tachysoides and O. harpaloides in Iberian populations.

The initial hypothesis was supported, as several samples of Ocys tachysoides were noticed among collection material previously identified as Ocys harpaloides and Ocys sp. (Table 1). The results of this work suggest that the recognition of O. tachysoides and O. harpaloides should not be assessed only by a superficial study of their external appearance, as individuals of both species could present atypical expressions of one or more diagnostic external characters (Fig. 1).

The microsculpture pattern was the most consistent external character in the studied material: microsculpture forming meshes, with lines not closely spaced, is typical of O. tachysoides, while microsculpture not forming meshes, with transverse lines closely spaced, is typical of O. harpaloides. W e must indicate that it could be difficult to distinguish the expressions of this trait without comparison material of the two species. The elytra coloration, elytra shape and shape of the hind angles of pronotum were, all of them, less consistent characters, as atypical expressions were detected in all cases in the two studied species. Thus, we suggest not considering typical expressions of these last three traits, but more or less common expressions (at least in the Iberian populations). The variability of elytra coloration in the two studied Ocys is illustrated for first time in the present work (Fig. 2). In O. tachysoides, the most common elytra coloration is entirely dark, contrasting with the paler head and pronotum (Fig. 2A). However, elytra in this species also could be reddish or brown, resulting in a poor or inexistent contrast between these three body parts (Figs. 2B, C). In O. harpaloides, the anterior and central regions of elytra are commonly paler than the lateral and posterior margins (Fig. 2D), but in some individuals the elytra coloration is uniform, more or less similar to the head and pronotum (Fig. 2E, F).

The new records of O. tachysoides provided in this work highly increase its chorological knowledge in the Iberian Peninsula. In this territory, the species is known from the central and northwestern regions, and it occurs in relatively humid locations with temperate climate and, frequently, mountainous orography (Fig. 3). In Spain, we provide the first records of O. tachysoides for the autonomous communities of Madrid and Castile and Leon, and we confirm its presence in Asturias. We also provide the second record for Portugal and the first one for the district of Montalegre.

From our samplings and the collection labels of the studied material (Table 1), we inform about different forest habitats (Fig. 4) in where O. tachysoides is present: mountain beech forest of Fagus sylvatica L. (Hayedo de la Pedrosa; Fig. 4A); gallery mixed forest of Betula alba L., Quercus robur L., Salix alba L. and Corylus avellana L. (Arroyo de Prao Viejo); woodland of Eucalyptus globulus Labill. close to freshwater (Ribadesella); mountainous pinewood of Pinus sylvestris L. (Arroyo de Majalvir; Fig. 4B). It is known that O. tachysoides can occur under bark of several tree species in forests and woodlands (NMNI, 2006; Maddison & Anderson, 2016). We confirm this behavior in our samplings, as O. tachysoides was collected removing bark from dead trees. Ortuño & Toribio (2005: 48) also did it for O. harpaloides, so both species may share this particular microhabitat. In addition, we indicate that studied material of O. tachysoides from Arroyo de Prao Viejo was collected by sieving leaf litter near a river stream. From all these data, we suggest considering humid forests as relevant habitats for O. tachysoides in the Iberian Peninsula.

Different suitable environments for O. tachysoides in this territory should be also considered. Part of the studied material (Table 1) could have been collected in humid but more open areas. Unfortunately, this information was not provided by collection labels. In fact, Toribio & Ramos Abuín (2018) collected the species under rolling stones in a riparian habitat (what is a more common behavior among Bembidiini).

Finally, with respect to the locations from where no data of O. tachysoides are available, we avoid suggesting real absences. New Iberian records of this species are expected to be noticed in the future. Considering the wide distribution of O. harpaloides (Ortuño & Toribio, 2005), safely both species co-occur in the Iberian territory, at least in the most humid environments and under some concrete conditions. More samplings are needed to understand the abiotic and biotic conditions in where populations of O. tachysoides develop.