For more than 30 years now, we have been gathering data on vespan activity in the field and laboratory under the influence of various factors. We found that light is most influential on the behaviour and activities of hornets (Hymenoptera, Vespinae); among various light wavelengths, the greatest influence was ascribed to the ultraviolet bandwidth (UVB). Prominent vespan activities outside their nest included digging, that is, the removal of soil from the nest, and we found this activity to take place at high noon, when the UV radiation, especially the UVB fraction, is maximal. In fact the digging activity of hornets was at times fully coordinated with the solar radiation, especially with the UVB portion of it, so that in daytime hours with diminished UV radiation, as in the morning or the afternoon, this activity and also flights outside the nest were accordingly curtailed, whereas at night there was no vespan flight at all. Under laboratory conditions, we found that hornets subjected to ether anaesthesia awaken faster when exposed to UV light than do control hornets left in the dark. In this connection, the exposure of pieces of hornet cuticle to UV light resulted in enhanced light absorption by the cuticle, but the absorption level reverted to normal after a period of rest in the dark. Tests for cuticular fluorescence after its irradiation with UVB light (290 nm) revealed a dominant emission in both UV and visible light. Furthermore, exposure of the cuticle of either live or dead hornets to light results in a photovoltaic effect which amplifies under UV irradiation. The hornet cuticle appears to behave like a semiconductor with traps and under the influence of light irradiation the electrical conductivity diminishes. The cuticle exposed to UV irradiation undergoes polarization, as do ferroelectric substances after being exposed to an electric field. The present paper summarizes the results of experiments and observations carried out on both live and dead hornets, from all of which emerges the conclusion that UV light is a factor which attracts hornets and influences them, while the hornets, in turn, utilize it for their own purposes. The latter utilization is achieved in cooperation with bacterial symbionts such as Staphylococcus xylosus and S. gallinarum.