The diel circadian rhythm consists of physiological cycles of circa 24 hours, which allow organisms to synchronize their activities to abiotic signals from their environment, primarily light. The circadian rhythm affects many arthropod behaviors and as a result it also affects the interactions between an arthropod and its environment. In agriculture, the daily timing of pesticide application was found to greatly affect efficiency in controlling pests. Little is known about the genetic mechanism controlling the circadian clock in mites and ticks. In this study we set out to study the diel circadian rhythm of the pest mite Tetranychus urticae. Furthermore, we examined the published, annotated genomes of >30 mites and ticks and searched them for key circadian genes We reared T. urticae mites under light:dark as well as constant light conditions and examined both gene expression and egg laying behaviours. In parallel, we selected key circadian clock genes and examined their presence and phylogeny in >30 species of mites and ticks. While unable to firmly link egg laying behaviour with a diel rhythm, we observed a preference of T. urticae females to lay eggs in early morning hours. Our results indicate the presence of a diel rhythm in T. urticae which will require further behavioural studies to uncover. When examining circadian genes’ expression, we see that we were able to disrupt gene expression by rearing the mites in constant light conditions. Finaly, our comparison of circadian genes in various Acariformes and Parasitiformes species hint at the presence of several circadian clock mechanisms within these superorders.