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Photo#2070379
Agabus in restored valley stream - Ilybiosoma seriatum - female

Agabus in restored valley stream - Ilybiosoma seriatum - Female
Sevenmile Creek, 8 km NW of Helena, Lewis and Clark County, Montana, USA
October 5, 2021
Size: 9.5 mm
Shiny black beetle, oblong-rounded, flattened body. Collected. Locally common in shallow water, especially mats of aquatic plants, at the cobbly margins of recently constructed stream channel, in water a few centimeters deep. At least 30 present in a 10 meter stretch. Stream floodplain disturbed in winter 2020-2021 by heavy equipment during stream restoration work. Large patches of bare ground, stands of exotic perennial grasses re-establishing, large patches of Chenopodium simplex and C. berlandieri with many ripe seeds, and patches of still-flowering Helianthus annuus and Sisymbrium loeselii. Early night, the first few hours after sunset. Smoky, wind calm varying to light breeze, partly cloudy, 75 F to 64 F.

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

Keyed to genus in Arnett & Thomas 2001. Some of the characters include metatarsal claws equal; scutellum visible; medium size; pronotum with lateral bead; and the ) ( shape of the metacoxal lines. Have requested Larson & Wolfe 1998 and will attempt to key to species when I get it. Placing at the family level for now since I'm not sure if Arnett & Thomas' Agabus corresponds to the current treatment.

Images of this individual: tag all
Agabus in restored valley stream - Ilybiosoma seriatum - female Agabus in restored valley stream - Ilybiosoma seriatum Agabus in restored valley stream - Ilybiosoma seriatum Agabus in restored valley stream - Ilybiosoma seriatum Agabus in restored valley stream - Ilybiosoma seriatum Agabus in restored valley stream - Ilybiosoma seriatum Agabus in restored valley stream - Ilybiosoma seriatum Agabus in restored valley stream - Ilybiosoma seriatum

Keyed to species in Larson et al. 2000
Moved from Predaceous Diving Beetles.

Within Agabus s.l., characters included the bead at the anterior margin of the clypeus discontinuous, with a wide non-grooved gap in the middle; the lateral bead of the prosternal process not inflated posterior of the procoxae; pronotum widest at the hind angles; impression in metasternum to receive the prosternal process extending almost to the level of the hind margin of the mesocoxae. This took me to the seriatus group; from there important characters were measurements of relative proportions of the body. The ratio of metacoxa to metasternal wing was 2.6. Metatibial length to width was 5.3. Overall length to width was 2.1. This combination of characters, supported by the apically infuscated palpi and antennomeres 3-11 apically infuscated, took me to A. seriatus (now transferred to Ilybiosoma). Female (protarsomeres lacking sucker-like hairs ventrally). This is a widespread species and its typically lotic habitat matches with my observation here.

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