At the family level, a comparison of three different mosquito genera (Aedes, Anopheles, and Culex, all in the Culicidae) has revealed prominent genus specific expansion of some immune gene families (Bartholomay et al., 2010) . Comparative studies of Drosophila species are particularly revealing, showing that novel immune genes and immune gene families have originated relatively recently, suggestive of a role of parasites in driving adaptive evolution in flies (Sackton et al., 2007) . Furthermore, for particular immune proteins, the amino acids under positive selection vary between Drosophila species groups, suggesting different fly species experience different parasite pressures (Morales-Hojas et al., 2009) . Insects with very different life styles, such as the social honey bees (Evans et al., 2006) and ants (Smith et al., 2011) , and symbiont-dependent aphids (Pennisi, 2009 ) likewise have immune systems that are surprisingly divergent from the Drosophila immune system.