The spectral sensitivity of polarized light orientation inCataglyphis bicolor (Formicidae, Hymenoptera)

Summary1.The desert ant,Cataglyphis bicolor, is able to orient towards the pattern of polarized light in the sky even without perceiving information on the sun's position. The accuracy of artificially induced homing courses is not influenced by performing the experiments just before sunrise and after sunset or by shading the sun.2.However, after destroying the polarization pattern by appropriate filtering of the skylight (Figs. 1 and 2) the azimuth of the sun was found to be sufficient when working as an isolated orientation parameter (Fig. 5). No influence of the sun's altitude could be shown by mirror experiments (Fig. 6b).3.By artificially shifting the sun's azimuth either during the foraging or during the return run the sun's azimuth competes with the polarization pattern. In that situation the sun has no influence on direction finding (Fig. 6a and b).4.The ants tested beneath various colour folios working as large sized spectral filters do not show any direction finding capacities as soon as wavelengths shorter than 410 nm are cut off (Fig. 7). This holds irrespective of whether the sun is visible or not. The accuracy of the homing courses is totally restored by means of an edge filter transmitting in the range λ λ 390 nm (Fig. 9).5.The results strongly support the hypothesis that only the uv.-receptors are involved in polarization analysis.