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Photo#2069847
Agonum at stream edge - Agonum errans

Agonum at stream edge - Agonum errans
Sevenmile Creek, 8 km NW of Helena, Lewis and Clark County, Montana, USA
September 14, 2021
Size: 8.5 mm
Shiny black beetle with coppery iridescence, crawling actively across cobbles at stream edge. Collected. Ruderal floodplain community with Kochia scoparia, Chenopodium simplex, Chenopodium berlandieri, Helianthus annuus, and Cleome serrulata. Midday to early afternoon, sunny, 66 F to 73 F, gentle to fresh W breeze, good air quality.

Elevation ca 4000 feet. Disturbed riparian corridor on stream restoration site within a patchwork of native and non-native grassland.

Keyed to genus in Lindroth 1961. Characters include 3 punctures on the 3rd elytral interval; 2 lateral punctures on the pronotum; mentum with median tooth; 2 punctures above each eye; epipleura not crossed; and tibiae slender, only slightly widened apically. Tentatively keyed to A. muelleri. 3 small punctures on the 3rd elytral interval, plus a possible 4th beyond the apex of the scutellar stria. Well-formed lateral pronotal bead connected to well-formed basal bead. Iridescence of elytra uniform. Several short setae present on the underside of the apical metatarsomere. Basal antennomere and legs rather pale, except tarsi dark. Epipleura dark, however, which does NOT match with the description of this species.

Images of this individual: tag all
Agonum at stream edge - Agonum errans Agonum at stream edge - Agonum errans Agonum at stream edge - Agonum errans Agonum at stream edge - Agonum errans Agonum at stream edge - Agonum errans Agonum at stream edge - Agonum errans Agonum at stream edge - Agonum errans Agonum at stream edge - Agonum errans

Moved based on closer study
Moved from Agonum.

Keyed to A. errans in Lindroth 1961 when I re-examined the specimen with a higher-powered microscope. The undersides of the apical tarsal segments threw me off originally in Lindroth's key, since there are 6 VERY short setae present (to get to A. errans I have to say they are glabrous underneath or with up to 4 inconspicuous bristles, these "notably in errans and quadratum"). Having previously gone the route of none-glabrous tarsal undersides (in which case the setae should be usually long, certainly not the case for this specimen), I had gotten to A. muelleri, whose description did not match the specimen (that species is not described with dark epipleura or clearly transverse elytral microsculpture). When I tried going the route of the nearly-ventrally-glabrous apical tarsomeres, this keyed very easily to A. errans and the description matches well. Characters of note include the relatively broad pronotum without sinuate margins but with often denticulate basal angles, and with large, rugose basal foveae, the lateral depression extending to the front angles; elytra with the striae punctulate; elytral microsculpture obviously transverse; legs rufous except tarsi; and brightly iridescent dorsum.

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