HOLOTYPE ♀ Belgian Congo [Democratic Republic of Congo]: Kafakumba, viii.1934 [CMNH].
Transferred to Falcatula by Kitching & Cadiou, 2000, Hawkmoths of the world: 46. Polyptychus penumbra was based on a pair of misshapen and badly prepared moths from southern Democratic Republic of Congo. Clark (1936) (STI 17261) characterized the species as “a drab insect, allied to P. falcatus R. and J. and to P. cymatodes R. and J., but much darker”. Carcasson (1968: 31) (STI 17169) suggested that Polyptychus penumbra “is probably no more than a dark form of Falcatula falcata [sic]”. Synonymized with Falcatula falcatus by Kitching et al., 2018, Biodivers. Data J. 6: e22236.
Examination of the series of Falcatula falcatus in NHMUK has shown that although many specimens from Shaba province of Democratic Republic of Congo and adjacent areas of Zambia are dark, many are rather paler and form a continuous series of intermediate colour forms with the generally paler specimens from eastern Africa. Kitching & Cadiou (2000: 29) (STI 18788) argued that, “Two taxa that are diagnosably distinct in habitus and/or structure and that come from widely separated localities but are connected by a series of intermediate forms in the intervening area are not treated as subspecies but simply as the terminal representatives of clinal variation”. Such is the case with Falcatula penumbra and Falcatula falcatus and consequently there is no justification for maintaining Falcatula penumbra as a species. As in many other Smerinthinae, the ground colour and pattern intensity of Falcatula falcatus is probably largely determined by environmental factors.