Ants accumulate and protect collective resources and, with the exception of nomadic species, live in a nest, which is considered to be one of the bases of the evolution of eusociality. Resources and/or protective services provided by ant colonies are exploited in manifold ways by an amazing diversity of other organisms acting as guests and/or parasites: viruses, bacteria, rickettsias, fungi, sporozoa, amoeba, ciliates, nematodes, trematodes, cestodes, mollusks, diplopods, crustaceans, mites, spiders, and a large variety of parasitic or parasitoid insects. Such associations can be obligatory or facultative, permanent or temporary, and harmful or beneficial for the host. Due to the diversity of interactions, an understanding of the nature of these relationships and the mechanisms of integration used by parasites as well as the defense strategies developed by their potential host remains a challenge. Parasites certainly raise particular selection pressures on colony phenotype, and, additionally, they may shape composition and dynamics of ant communities. Over the past two decades, a growing interest has emerged for studying the impact of parasites on colony phenotype and their role in the ecology and evolution of their hosts. Despite their apparent importance, detailed knowledge is lacking, for example, about diversity and abundance of ant parasites or selection pressures imposed through parasitism on host reproductive strategies. In this special issue of Psyche, we will give specific attention to both the mechanisms used by ant parasites to integrate into their host colony and to the way parasitism pressure could affect patterns of reproduction and life history in ant hosts. We invite investigators to contribute original research articles as well as review articles on various aspects concerning ants and their parasites. Potential topics include, but are not limited to:

• Biodiversity of ant parasites
• Dynamics of host-parasite association
• (Co)evolution and phylogeny
• Host specificity
• Hyperparasitism, superparasitism, and multiparasitism
• Mechanisms of integration in host colonies and host defense
• Natural history and behavior
• Community impact of ant parasites
• Potential for biological pest-ant control
• Life cycles and reproductive strategies
• Reciprocal fitness impacts (symbiosis, mutualism, commensalism, and parasitism)

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