The eyes of male and female Rhagophthalmus ohbai are of very different sizes and possess approximately 3000 and 35 facets, respectively. In the male eye one can distinguish a smaller dorsal region with 500 facets and a larger ventral one with ca. 1800. Ultrastructural differences between them have been described earlier in this journal (Lau and Meyer-Rochow, 2006). Electrophysiological recordings from the two eye areas have now revealed that the ventral region is maximally sensitive to light of 600 nm wavelength, while the dorsal eye region responds maximally to light of 540-560 nm wavelengths. In the dorsal eye region sensitivity to UV-radiation at around 360 nm wavelength, being twice as high as that of the ventral eye region, amounted to ca. one quarter of peak wavelength sensitivity. The regional differences in spectral sensitivity seem to be a reflection of the different tasks of the two eye regions: looking downward to see the yellow light emitted by a female, sensitivity towards longer wavelengths would be advantageous, but looking upward into the twilight sky, sensitivity to shorter wavelength would be a more appropriate adaptation.