Polarization Sensitivity and Polarotaxis in Springtails (Collembola)

The anatomy, photoreceptive structure and optics of the two ocellar fields on the head of poduromorph springtails (Collembola) are here summarized. The water-surface-inhabiting Podura aquatica springtails have the ability to estimate both the degree and the angle of polarization. They are attracted to linearly polarized light, the polarization direction of which deviates from the horizontal by less than 50°. Horizontally polarized light attracts more springtails than unpolarized, even if the polarized stimulus is 10 times less intense. The polarization sensitivity threshold in Podura aquatica is between 10% and 26%. The bimodal phototactic response of Podura aquatica is strongest in the blue (484 nm) and green-yellow (570 nm) spectral ranges, while their polarotaxis operates in the blue (484–492 nm). This polarotaxis ensures water detection, while phototaxis helps the recognition of the riparian zone.