Full spectrum lighting induces behavioral changes and increases cortisol immunoreactivity in captive arachnids

The use of full spectrum illumination, including ultraviolet (UV), during captive husbandry of arachnids such as scorpions and theraphosids (tarantulas) is common practice in zoological institutions and amongst some hobbyists, as confirmed by a survey undertaken in this study. The effect of such lighting on captive arachnids has not been previously investigated. Comparison of key behavioral changes and haemolymph cortisol immunoreactivity was undertaken with and without full spectrum lighting. Two representative large arachnid species - king baboon spiders, Pelinobius muticus and Indian giant scorpions, Heterometrus swammerdami were selected for the study. Both organisms spent all their time hidden when exposed to full spectrum light compared to low-level ambient light except for one instance, in one spider, for one observation. There was no significant difference in burrowing and webbing in P. muticus when exposed to full spectrum lighting. There was a decrease in the number of behaviors or postures expressed in full spectrum lighting compared to ambient light for both species. Cortisol immunoactivity of both species were significantly elevated after exposure to full spectrum lighting compared to the same period of ambient light. This study provides the first evidence of detectable cortisol immunoactivity in arachnid haemolymph. These levels changed in response to full spectrum illumination and were linked to behaviorial changes. This suggests that a common husbandry practice may be detrimental to these animals.