Baetis vernus, Curtis, 1834

Webb, J. M., Jacobus, Luke M. & Sullivan, S. P., 2018, The state of systematics of North American Baetis Leach, 1815 (Ephemeroptera: Baetidae), with recommendations for identification of larvae, Zootaxa 4394 (1), pp. 105-127 : 119

Baetis vernus group

This group currently consists of the following North American species: B. brunneicolor , B. bundyae , B. hudsonicus , and B. vernus . The species group is distinguished from other North American groups by the absence of robust setae from the antennal scapes and pedicels, paraprocts, gills, and abdominal sterna and terga, and by the well-developed medial projection on labial palp segment two. All species of the vernus group are extremely similar and difficult to distinguish as there are no apparent differences in mouthparts and all have a similar color pattern of brown abdominal terga with diffuse pale areas laterally and frequently a thin, pale median line (Fig. 6) although the size and sharpness of the pale areas varies greatly within species. The pronotum has previously been described as uniformly colored (Morihara & McCafferty 1979; Wiersema et al. 2004), but in most freshly collected specimens we have examined, we observed various pale and dark markings, and frequently a pair of bilobed, pale markings submedially ( Fig. 52). Larvae of two species have very elongate, narrow gills. Cryptic species have not yet been observed in the North American representatives of the B. vernus group, but have been found in the Palearctic species (Savolainen et al. 2007; Ståhls & Savolainen 2008).

Baetis bundyae and B. hudsonicus are most commonly found in the northern parts of North America, although B. bundyae has been reported from Wyoming ( Durfee & Kondratieff 1999) and Minnesota ( Lager et al. 1982). Larvae of B. bundyae and B. hudsonicus are distinguished by the relative lengths of their median caudal filaments. This character is known to be variable in many baetids, including in B. hudsonicus , but the two species form distinct barcode clusters (Webb et al. 2012). However, we emphasize that caution should be exercised when applying the names of these two species.

Baetis vernus complex: The Baetis vernus complex includes B. brunneicolor and B. vernus . Baetis brunneicolor is widespread throughout North America, but it is most common in the north and midwest; recently, the species was reported from scattered western localities, including Washington and Idaho ( McCafferty & Meyer 2007). The report of a single specimen of B. vernus based on mtDNA ( Cordero et al. 2017) complicates the identification of the vernus group in the north as B. vernus is nearly identical to larvae of B. brunneicolor based on detailed descriptions provided for European specimens (Muller-Liebenau 1969; Bauernfeind & Soldán 2012). The cytochrome oxidase 1 sequence of the North American specimen of B. vernus ( Cordero et al. 2017) is nearly identical to, and in the same BIN as, those of specimens from Finland (Ståhls & Savolainen 2008). Although B. vernus is widespread throughout the Palearctic as far south as Turkey and Greece ( Bauernfeind & Soldán 2012), mtDNA suggests the northern populations of B. vernus are likely not conspecific with those from Germany (Morinière et al. 2017). Given that the BIN to which the North American specimen of B. vernus belongs is only reported from the far north in the Palearctic, it is reasonable to assume a similar distribution in North America. Until characters can be found to differentiate larvae of B. vernus and B. brunneicolor , specimens North America should be identified only as B. vernus complex, especially for northern specimens.