Water bug seined from shallow water of pond near emergent cattail stand - the same pond from which I also collected N. kirbyi on the same date. Very silvery forewings. Collected. Pond created in winter 2020-2021 from old, incised stream channel by heavy equipment during stream restoration work. Unusually warm evening about 5 days after 1 inch of snow fell, now melted. Dusk, high clouds, 66 F to 62 F, gusty breeze varying from light to fresh.

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

Notonecta have eyes separated dorsally, and lack a pit at the anterior end of the claval commissure. The former separates them from Martarega and the latter from Buenoa. Keyed to species using the key to common Notonecta in Slater & Baranowski 1978. Combination of fourth apparent abdominal segment without a bare central area; the scutellum entirely black; and the forewings mostly pale with a dark crossbar beyond the tip of the claval commissure narrows the field to N. undulata and N. indica. N. indica "closely resembles undulata in size and color but often has the dark wing markings more extensively developed, frequently as complete black transverse band which will separate indica from 'typically' colored specimens of undulata with which it is often confused." Based on the illustrations in Slater & Baranowski, my specimen closely matches N. undulata and the black band does not appear wide enough for N. indica; moreover, the distribution of N. indica is "across the entire southern United States usally below 37 N. latitude," so it appears at best an improbable species for Montana. In the key, the distinguishing characteristic between these two is "length of head subequal to maximum interocular distance" for N. undulata, vs. median length of head longer for N. indica (with specimen horizontal). I took a completely horizontal photo of this specimen under the microscope and used pixel measurements to get a ratio of median head length/maximum interocular distance of 0.91, clinching the ID. *Note: the Slater & Baranowski key does not include all of the species in North America, so to confirm this ID I consulted the distribution of North American Notonecta listed in Hungerford 1933. Of these species, the only one not included in this key that might be present in Montana is N. spinosa. Based on BugGuide comments by Brady Richards, N. spinosa has the mesotrochanter spinose; it was rounded in this specimen. Therefore, I am confident that this is Notonecta undulata.

This (along with an individual from this site in 2020 that I was just now able to identify) are the first BugGuide records for this species in Montana, but it is well within the expected range, which Slater & Baranowski list as "throughout the United States but becomes scarce and local in the southern states and west of the Rocky Mountains."