After the previous papers on the genus (Horn (1905), Kippengan (1997)), 20 recognized (and one uncertain) Oxygonia species were presented recently by Moravec (2020), occurring mostly along the Andean mountain streams and distributed from Costa Rica and Panama to Colombia, then southwards to Ecuador, Peru and northern Bolivia. Interestingly enough, Oxygonia nigricans W. Horn, 1826 was originally described from a maritiam habitat of the small Georgona Island off the Colombian Pacific coast, yet in Panama was later caught on Rio Cana at altitude 500 m. Fourteen recognized taxa occur in Ecuador, six of which are Ecuadorian endemics.

Some species of this genus can be recorded during the day, some at night, and some both, during day and night. Individuals are mainly found on partially flooded, rather larger boulders and stones, usually in the middle of fastflowing streams with a width of 1 to 15 m, where they search for prey of smaller aquatic insects. Most species, when disturbed and according to the natural character of the water course, fly to another boulder in the stream or a rock on the bank or to the leaves of coastal vegetation reaching above the water surface, where they also rest during periods of inactivity.

Oxygonia oberthueri (Fig. 13) was the only species of this genus recorded on studied localities. Pearson et al. (1995) published the results of natural history observations on nine Ecuadorian species of Oxygonia. They mentioned diurnal activity of Oxygonia oberthueri, that forages on rocks and moss-covered vegetation near the water’s surface. It regularly flies to overhanging foliage to escape danger. It is found along small (<1 m wide) streams to moderate rivers (> 15 m wide) from 300‒1300 m elevation.

Our observations confirm both diurnal and nocturnal activities. The nocturnal activity seems to be preferred by this species according night vision observation however the same behaviour was observed during the day and night. The individuals move quickly on boulder surfaces and often fly from one to another. The mating pair was observed during the night when the female foraged undisturbed during mating. The male held the female with his mandibles on the upper part of her elytra, not in metepisternum as presupposed.