Sphinx formosana Riotte, 1970, Ent. Z., Frankf. a.M. 80: 14. Type locality: Central Formosa [Taiwan, Nantou Hsien], Wushai [Jenai].
A close relative of Sphinx crassistriga crassistriga (Rothschild & Jordan, 1903) from Japan, but wings much narrower, forewing with apex falcate, hindwing with apex pointed. Forewings with a general dusting of pale grey scales over the upperside.
Male genitalia similar to those of Sphinx crassistriga crassistriga, but: valve more robust; harpe with outer margin dentate at dorsal half, ventral edge more produced; saccus longer; sacculus characteristically with a strongly toothed outer edge; aedeagus sigmoidal, ending in a curved point and with a subapical lateral convexity.
A montane species, occurring above 2000m altitude.
Taiwan: vi (Nantou Hsien; Taichung Hsien); 2.vii (Ilan Hsien).
Larval hostplants. Unknown.
Taiwan: Nantou Hsien (Jenai); Ilan Hsien (Taipingshan); Taichung Hsien (Tashiiehshan, Anmashan, 2230m).
Endemic to the northern central mountains of Taiwan.
Part of the relict eastern Palaearctic fauna of montane Taiwan. Closely related species are found in Japan (Sphinx crassistriga crassistriga Rothschild & Jordan, 1903) and southwest mainland China (Sphinx centrosinaria Kitching & Jin, 1998).