The species of this genus are recorded on all continents (Noyes, 2001).

Pnigalio belongs to the tribe of Eulophini by having funicle 4 segmented, propleura meeting posteriorly and covering prosternum, 2 pairs of scutellar setae and 3 or more setae on submarginal vein.
Pnigalio and Ratzeburgiola, may be distinguished from other Eulophini (Dicladocerus, Hemiptarsenus, Notanisomorphella Girault, Stenomesius and Sympiesis) by having plicae and a costula on propodeum. These genera may also be distinguished from Pnigalio as follows: Dicladocerus has 2 branches on male funicle and longitudinal lines on scutellum; Hemiptarsenus has a long scape distinctly exceeding apex of vertex; Notanisomorphella has a step-like plica and the propodeum is distinctly sculptured; Stenomesius has yellow coloration, notauli complete, longitudinal lines on scutellum, two median carina H- or X-shaped and doesn’t have branches on male funicle.
Finally, Ratzeburgiola appears to be close to Pnigalio, as they both have plicae and costula on propodeum; however, Ratzeburgiola has notauli which are present (complete or almost complete and converging posteriorly) and the scutellum shiny with sublateral lines (Schauff et al., 1998).
Recent keys to Pnigalio are available for North American species (Yoshimoto, 1983). Older but still useful keys may also be Graham (1959) and Askew (1968) for the British species, and Miller (1970) for the Nearctic region. In those keys however there are several species that have subsequently been renamed or synonymised (Noyes, 2001).