Diagnosis Body brown, with area between ocellar triangle and compound eyes paler; fore legs light brown, mid and hind legs brown, tarsi and apex of tibiae yellow.Antennal segment I light brown, II brown, III–IV brown with lighter bases and apexes, V pale, VI brown and VII–VIII light brown to pale; fore wings brown with pale spot sub-basally. Head strongly sculptured, constricted behind eyes and basally. Antennae 8-segmented, III & IV with short apical neck and forked sense cones, on IV the cone extends to about two thirds of segment V. Pronotum reticulate, without internal markings. Mesothoracic endofurca without spinula, metathoracic endofurca without spinula and with stout arms, reaching mesothorax. Mesonotum without a median longitudinal split. Metanotum reticulate, without a strong triangle; one pair of robust setae; campaniforme sensilla present medially. Tarsi 1-segmented. Fore wings with first row of setae interrupted medially, three setae distally; second row with 9 to 11 setae equally spaced between them; setae thin, wing cilia wavy. Abdominal tergites III–VIII with oblique striae on lateral thirds, some reticles submedially; median setae short and distanced from each other; posterior margins with craspeda; tergite VIII with teeth arising from craspedum on lateral thirds; X without a longitudinal split. Abdominal sternites with three pairs of setae, pairs 1 and 2 near posterior margin, 3 ahead of posterior margin. Both sexes macropterous.
Male similar to female, but smaller; abdominal sternites V–VII with concave and transverse pore plates on the median third.
Intraspecific variation The number of setae on the forewing's second vein varies from 9 to 11.
Genus and similar species information The genus Oneilliella has five Neotropical species, all with a dark and strongly reticulated body; metanotum sculpture not forming a strong triangle; metafurca stout and long, without spinula, reaching the mesosternum; and abdominal tergite X without a complete longitudinal split. Among the three Brazilian species, Oneilliella wanessae has antennomere III with the shortest apical neck, and forewing setae thin.A key to the Neotropical species of Oneilliella is available in Lima et al. (2023).
Distribution around the world Described from Brazil.
Life history Unknown, possibly phytophagous. Many specimens from the type series were collected from bamboo (Chusquea sp.), but without the presence of larvae.
