Baetis, Leach, 1815

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 : 120-121

Key to larvae of North American Baetis species (larvae of B. rusticans and B. diablus unknown)

1 Labial palp short and broad, distinctly convex laterally, and with small medial projection on segment 2 (Figs. 19–21); prono-

tum usually with submedian dark, inverted U-shaped markings (Fig. 53), but in darkly colored specimens only pale area within and lateral to ‘U’ may be evident (Fig. 12); femora usually with large median quadrate dark marking (Fig. 34), but may be more elongate in western specimens (Figs. 35, 36); pedicels, paraprocts and abdominal sterna without robust setae ( Baetis fuscatus group).......................................................................................... 2 - Labial palp usually more elongate, with or without a distinct medial projection on segment 2, and only slightly convex laterally (Figs. 17,18, 22–27); pronotum variable (Figs. 51, 52, 54), rarely with inverted dark U-shaped markings; femora variable; pedicels, paraprocts and abdominal sterna with (Figs. 31, 33) or without robust setae................................ 4

2 Abdominal terga 2–4, 6–8 each with three small, similarly sized round, pale markings near posterior margins (Figs. 15, 16), although markings may be reduced (Fig. 14) or abdominal terga nearly uniformly dark with submedian pair of pale parenthesis-shaped markings (Waltz et al. 1996: Fig. 1); caudal filaments with a median dark band; east of Rocky Mountains ( B. intercalaris and synonym; comprised of at least 6 BINs)..................................... Baetis intercalaris complex

- Abdominal terga with two large sublateral pale markings near posterior margin and a small anteromedian pale marking (Figs. 11, 12) or with sublateral and anteromedian marking fused to form ‘crown’ shaped pale marking (Figs. 8, 9, 13); caudal filaments with or without dark median band................................................................... 3

3 Caudal filaments with dark median band (Fig. 11); abdominal terga usually with anteromedian and sublateral markings separate and with tergum 5 distinctly paler than adjacent terga (Figs. 11, 12) and with distinct subquadrate dark marking on femora (Fig. 34); specimens from Pacific Northwest with some fusion of sublateral and anteromedian spots and with tergum 5 similarly marked to adjacent segments (s. 8, 9) and with variably sized elongate dark markings on femora (Fig. 35, 36); widespread ( B. flavistriga , B. phoebus , and likely B. rusticans ).................................... B. flavistriga complex

- Caudal filaments uniformly pale; abdominal terga 2–8 with sublateral and anteromedian pale markings fused to form ‘crown’ shaped pale area (Fig. 13); femora with indistinct or elongate dark marking; mostly southwestern but reported as far north as Washington and Idaho ......................................................................... Baetis notos

4 Scapes and/or pedicels (Fig. 33), paraprocts and abdominal sterna (Fig. 31) with robust setae in addition to fine setae and scales; pronotum usually with pair of dark, bilobed markings (Figs. 2b, 51) ( Baetis rhodani group)..................... 5

- Pronotum without pair of dark, bilobed markings, but may have pale bilobed marking (Fig. 52); scapes and/or pedicels, paraprocts, and abdominal sterna with only fine setae and scales..................................................... 9

5 Gills with fine and robust setae on margins (Figs. 39, 40), serrations present or absent............................... 6

- Gills with only fine setae and serrations on margins, robust setae absent (Fig. 41)................................... 7

6 Abdominal terga with robust setae near posterior margins (as in Fig. 30); gill margins smooth (Fig. 40); paraglossae with 5 subapical rows of setae; labial palps slender, length segment 2>2× basal width of segment 3 (Fig. 25)....... Baetis magnus

- Abdominal terga without robust setae; gill margins serrate (as in Fig. 41); paraglossae with 3–4 subapical rows of setae; length of labial palp segment 2 <2× basal width of segment 3 (Fig. 26)....................................... Baetis adonis

7 Median caudal filament reduced to 1–2 segments (Fig. 32).................................................... 8

- Median caudal filament with at least 3 segments, usually>20% length of cerci in mature specimens and with fine setae laterally................................................................................................ 13

8 Gills> 2× longer than wide; far Northern ........................................................ Baetis foemina

- Gills <2× longer than wide; widespread in western areas ( B. bicaudatus and synonym; includes at least 4 BINs).......................................................................................... Baetis bicaudatus complex

9 Labial palps slender and elongate, with inner margin of segment 2 straight or convex (Fig. 18); labrum usually longer than wide and tapered distally (Fig. 29); abdominal tergum 5 distinctly paler than adjacent terga (Fig. 1) ( Baetis alius group)... 10

- Labial palps with distinct medial projection, with inner margin of segment 2 concave (Fig. 17); labrum wider than it is long (as in Fig. 28); abdominal color pattern with all terga similar, usually with thin pale median line and pair of diffuse pale sublateral markings (Fig. 6) ( Baetis vernus group)................................................................... 11

10 Eastern North America; caudal filaments with median dark band....................................... Baetis pluto

- Western North America; caudal filaments without medial dark band.................................... Baetis alius

11 Gills length>2.5× width, usually more than 2.5 abdominal segments in length (Figs. 6, 42); mostly far northern in distribution................................................................................................... 12

- Gills length <2× width, less than 2 abdominal segments in length (Fig. 45); widespread ( B. brunneicolor and B. vernus )........................................................................................ Baetis vernus complex

12 Median caudal filament subequal in length to cerci............................................. Baetis hudsonicus

- Median caudal filament length> 0.8× length of cerci............................................. Baetis bundyae

13 Pronotum with pair of dark bilobed markings (Figs. 2b, 51); gills length <2.0× longer than width; labial palp segment 2 with distinct median projection (Figs. 22, 23); abdominal terga with only fine setae, scales, and scale bases; tarsal claws usually with pair of fine subapical setae; fore femur length <3.0× width, mid- and hind femora lengths each <3.5× respective widths; outer incisors of mandibles with at least 3 teeth (Figs. 46, 47); widespread ( B. tricaudatus and 6 synonyms; comprised of at least 16 BINs)................................................................... Baetis tricaudatus complex

- Pronotum dark medially, without dark bilobed markings (Figs. 3, 54); gills length 2.0× width (Figs. 43, 44); labial palp segment 2 with poorly developed median projection (Figs. 24, 27); abdominal terga with robust setae, especially near hind margins, in addition to fine setae, scales, and scale bases (Fig. 30); tarsal claws without subapical pair of setae; fore femur length>3.0× width, mid- and hind femora lengths>3.5× widths; outer incisors of mandibles fused into single scraping blade (small secondary tooth may be present) (Figs. 48-50); Rocky Mountains and westward ( B. piscatoris , B. palisadi , B. persecutor ). .................................................................................. Baetis piscatoris complex