Female macropterous. Body and legs brown, fore tarsi and apex of fore tibiae paler; antennal segment III yellow in basal half or two-thirds but brown distally, IV–IX brown; forewing brown at extreme base including entire clavus, median brown area long, continuous along posterior margin, distal clear area not transverse, with costal vein dark.
Head with postocular region as long as eye length; distal maxillary palp segment subdivided. Antennae 9-segmented, III–IV with sensorium curving around apex, weakly sinuous and extending to basal third of segment, with prominent discoidal internal markings. Mesonotum with 2 pairs of accessory setae medially. Metanotal reticles with internal dot-like markings. Abdominal tergite I transverse lines antero-medially; trichobothria on X no larger than base of major setae on X. Sternites with 4 pairs of marginal setae, 4 to 7 pairs of discal setae laterally but none medially; sternite VII two pairs of accessory setae not distinguished from marginal setae.
Male similar to female but smaller, antennal segment III more extensively shaded. Maxillary palp distal segment with only one small subdivision. Antennal sensoria internal markings weak. Abdominal tergite I with two longitudinal ridges. Sternites with few discal setae, arising laterally, IX with only one or two discal setae.
The genus Desmothrips is known only from Australia, with 18 described species (Pereyra & Mound, 2010). D. bagnalli is closely related to D. australis and D. propinquus, but has distinct discoidal marking within the linear sensoria on antennal segments III and IV.
Known only from Australia
This species appears to be most common in souteastern Queensland, but has also been taken near Canberra. It is not known from Western Australia.
Collected from various flowers, with no known specificity.
Adults have been found in low numbers in various flowers.