Lighting and behaviour in captivity: Butterflies prefer light environments containing UV wavelengths

The behaviour and welfare of animals in captivity is of great importance to zoological collections, captive breeding programmes, food production and keepers of companion animals. Artificial lighting is commonly deficient in UV wavelengths, and use of such lighting for indoor animal enclosures could have significant impacts on the behaviour and welfare of animals to which UV wavelengths are visible. This includes birds, reptiles and fish, but also insects. Here we investigated the effect of UV-present and UV-absent light environments on the behaviour of Vanessa cardui, a butterfly that possesses a trichromatic visual system typical of many insects. We conducted behavioural experiments using a free-flight arena divided in half, where each half could be subjected to UV+ or UV− illumination. When lighting conditions for the two arena halves were the same, we found no significant differences in activity between UV+ and UV− light environments. However when lighting conditions for the two arena halves were different, butterflies showed a significant preference for the UV+ over the UV− half. This remained the case even when the overall intensity of UV+ illumination was less than that of UV− illumination. Our results suggest that UV-deficient artificial lighting conditions do not themselves affect the activity of butterflies, but that given a choice, butterflies prefer lighting that contains UV. Based on these findings, captive light environments can be designed that use supplementary lighting or filters to improve the welfare of captive insects, and the visitor experience.