Bizarrifrons Eichler, 1938

Type species: Nirmus magus Nitzsch [in Giebel], 1866, by original designation.

Bizarrifrons belongs to the Brueelia -complex (also including the genera Brueelia Kéler, 1936; Sturnidoecus Eichler, 1944; Formicaricola Carriker, 1957; Formicaphagus Carriker, 1957; Buerelius Clay & Tandan, 1967 and Furnariphilus Price & Clayton, 1995) that was defined by Clay & Tandan (1967) as having the following characters: (1) head with ventral carina interrupted medially and passing forward each side to or towards the anterior margin of the head; (2) lobes of the pulvinus attached to a flattened area parallel to that of the other side; (3) pronotum with one postero-lateral seta on each side; (4) meso- and metanotum fused forming a distinct pterothorax; (5) episternum III laterally sclerotised. Bizarrifrons is unique in the Brueelia -complex by its male genitalia structure and by the asymmetry of its preantennal region. In addition to those proposed by Eichler (1938), useful characters to separate the species within this genus are the level of the asymmetry in the head front, the size of the conus in relation to the length of the antennal scape, the shape of the tergal and sternal plates, the shape of the subgenital plates in both sexes, presence or absence of fenestrae on male subgenital plate (Figs. 43–46 vs. Fig. 36), the tergal chaetotaxy and the male genitalia. Although we have observed differences in the sclerotization of the temporal carina above the eyes, we consider it to be an unreliable character, which is not easy to define and measure.

Although all species of Bizarrifrons are still poorly known, it is possible to define two species-groups based on characters given in their original descriptions: (1) the magus species-group—including B. magus; B. maculatus; B. francisi (Carriker, 1903); B. clayae Eichler, 1938; B. meinertzhageni Eichler, 1938; B. latifrons sp. nov. and B. wecksteini sp. nov. —found on birds of the genera Psarocolius and Quiscalus, with sparse tergal chaetotaxy and tergal plates not entirely pigmented in both sexes, and (2) the picturatus species-group—including B. picturatus Carriker & Díaz-Ungría, 1961; B. juruani Carriker & Díaz-Ungría, 1961 and B. quasisymmetricus sp. nov. —found on species of Cacicus, with dense tergal chaetotaxy and tergal plates entirely pigmented (except for the area around the spiracles) in both sexes.