Cortex glia constitute about 20% of the glia in the adult Drosophila brain (Kremer et al., 2017), but this subtype is relatively understudied in flies. Based on our results, cortex glia express PER protein similarly to the pacemaker neurons albeit at a much lower level even in young flies. However, we cannot exclude that cortex glia in other brain regions could show higher PER levels. Cortex glia are presumed to provide trophic support to the neuronal cell bodies they envelop (Edwards and Meinertzhagen, 2010). A recent study supports this idea by demonstrating that genes involved with β-oxidation are expressed in cortex glia suggesting that these cells may generate and transport ketone bodies (Schulz et al., 2015). Cortex glia are known to produce Ca+2 oscillations and disruptions of these oscillations by mutations in the glial-specific Na+/Ca2+, K+ exchanger encoded by zydeco significantly decrease seizure threshold in flies (Melom and Littleton, 2013). While cortex glia are important for neuronal health and function, the role of potentially low amplitude PER oscillations in these cells has yet to be addressed.