Opening paragraph: Parasites are both numerous and ubiquitous, and so all living organisms face a continual struggle to fend off a constant barrage of immunological insults within their environment. The mechanisms for doing so are many and varied; they include physical and chemical defenses, such as thick skin, fur, or cuticle; behavioral defenses, such as grooming, behavioral fever, and self-medication; and immune defenses, including the innate immune system
common to all animals and the vertebrate-specific acquired immune system (Schmid-Hempel, 2011; Wilson, 2005). Since the advent of molecular advances such as whole-genome sequencing and next-generation techniques, our mechanistic understanding of immune defenses has grown considerably for both vertebrates and invertebrates. Amongst the many things these have revealed is the similarity between many aspects of innate immune defences of vertebrates and invertebrates (Vilmos & Kurucz, 1998), and this has highlighted the utility of using insects, especially Drosophila, as model hosts for understanding the evolution of, and plasticity in, the innate immune response.