Adding aromatic herbs and plants to your hen's nestbox can be an enriching treat. They can also be useful for repelling insects and ectoparasites.
Tomás G, Merino S, Martínez-de la Puente J, Moreno J, Morales J, Lobato E, Riverode Aguilar J, Del Cerro S. 2012. Interacting effects of aromatic plants and female age on nest-dwelling ectoparasites and blood-sucking flies in avian nests. Behavioral Processes.