Circadian rhythms are vital for physiological processes and are maintained by an endogenous mechanism that, in Arachnids, show extreme ranges from 19-29 hours. Alterations in the function of the molecular machinery could be the cause. Here, functional domains of putative spider circadian regulators were cloned into expression plasmids for cell culture analysis, laying the groundwork for comprehensive in vitro and in vivo spider circadian rhythm studies to better understand key differences between these circadian clocks.