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Within Alberta there are two other species which may be confused with Notonecta kirbyi: N. borealis and N. undulata. Of these, N. borealis occurs only in the boreal region and N. undulata is found across all of North America (Brooks and Kelton 1967, Hungerford 1917). As an adult N. kirbyi is the largest of the Alberta Notonectids (12-15 mm). Notonecta borealis may be differentiated from N. kirbyi by its white head, scutellum and hemelytra. As there is a great deal of variation in N. undulata it may be difficult to tell it apart from N. kirbyi by colouration. The head to propleuron of N. kirbyi is greenish yellow and the scutellum is always black, whereas N. undulata may be variable colours including yellow, green and has a black scutellum. Brooks and Kelton (1967) use morphological differences in eye colouration and the space between the eyes at the vertex of the head to distinguish very similar-looking individuals. Notonecta kirbyi's eyes are red, and the space between them at the vertex is about one half the distance of the distance between the perimeter of the eyes at the frons. Notonecta undulata's eyes are black. The distance between its eyes at the vertex is less than one half of the total distance between the perimeters of the eyes at the frons. Keel hairiness always reliably tells the difference between the two species under a dissecting microscope. Notonecta kirbyi has a bare keel on the fourth abdominal sternite that is hairy on both sides (Brooks and Kelton 1967). Notonecta undulata has a line of hair on the fourth abdominal sclerite keel (Brooks and Kelton 1967). The most distinguishing feature of N. kirbyi are its large, cloudy bands stretching across the leathery section of the hemelytra (from the inner edge of the clavus to the outer costal margin). Notonecta kirbyi is synonymous with N. insulata (Uhler), N. insulata var. impressa, N. (Paranecta) kirbyi (Henry and Froeshner 1988).

Very little is known about the life history of this organism (Rice, 1954). The eggs are approximately 2.2 mm long, the largest of any notonectid, and the hard chorion has puncture marks for respiration (Rice 1954). A mucilaginous sheath attaches eggs to substrates (Rice 1954). Development to the adult stage through five instars takes ~50 days (Rice 1954). Emergent adults do not develop ova as late as November, thus it is presumed they over-winter as adults (Rice 1954). Instars 1-4 hunt in the upper 50 cm of the water column (Streams 1992). The fifth instar and adults hunt below 50 cm depth in the water column (Streams 1992). Notonecta kirbyi displays the longest foraging dives of any Notonectinae measured: up to 14.6 minutes, seven times that of the next highest species N. undulata (Streams 1987). This species is rarer than the ubiquitous N. undulata (Rice 1954, Streams 1992) either because it prefers muddy habitat or because we haven't looked hard enough.

First and second instar nymphs have been noted to feed on crustaceans (Murdoch et al 1984) third instars and larger feed on larger prey like dytiscid larvae, mayflies, and terrestrial species that fall onto the surface of the water (Murdoch et al 1984). This species will devour anything it can subdue.