 Parasitic organisms can cause significant harm to their hosts, leading to reduced fitness. Insects have evolved various behaviors to defend themselves from these parasites, including avoidance of infected individuals, reduction of parasite growth, and alleviation of disease symptoms. These behaviors provide strong protection against parasites and parasitoids and can be used to understand how host-parasite interactions shape evolutionary trajectories. Behaviors can also influence the evolution of non-behavioral physiological immune systems as well as local adaptation and co-evolution between hosts and parasites. This article was authored by Thierry Lefebvre and Jacobus C. Derude.