The spectral cues used in the bee's celestial compass are investigated by presenting bees dancing on a horizontal comb with unpolarized (or polarized) spectral stimuli. Where appropriate, the use of e-vector information is prevented by painting out the specialized dorsal margin of the bee's eye (POL area, Fig. 1). This area has been shown to mediate e-vector information (Fig. 3; Wehner 1982), whereas the remainder of the dorsal retina is sufficient for mediating spectral information (Fig. 4).
Spectral cues are used by the bees to discriminate between sun and sky (Fig. 4). According to physical reality (Fig. 2), a long-wavelength stimulus is taken as the sun, whereas a short-wavelength stimulus is expected by the bee to lie anywhere within the antisolar half of the sky (Figs. 5 and 6). This is in accord with the bee's e-vector compass in which e-vectors are confined to the antisolar half of the sky (Fig. 9).
In general, spectral cues do not provide precise compass information except when a full celestial colour gradient is available including the solar and the antisolar meridian (Figs. 7 and 8).