Ant-isopod interactions: spanning predation, facilitation, and myrmecophily

Ants and terrestrial isopods are two key groups within soil ecosystems both in terms of their biomass and the vital functions they contribute to. Despite the ecological importance of both groups and their frequent interactions, the dynamics between ants and terrestrial isopods remain poorly understood. We provide a systematic overview and discuss the diverse spectrum of ant-isopod interactions ranging from predation, through facilitation, to myrmecophily. A limited number of ant species, restricted to the genus Leptogenys, specialize in preying on isopods, while a very broad group of ants opportunistically include them in their diet. To evade ant predation, terrestrial isopods employ defensive strategies such as avoidance, conglobation or secretion of repellent substances. Apart from the direct negative impacts of predation, ants impose several non-lethal effects on terrestrial isopods, influencing their spatial distribution, behaviour, and fitness. Invasive ants may, in contrast, indirectly benefit isopods by feeding on their predators or competitors. A diverse group of isopods are not deterred by ants and reside in their nests. These myrmecophilous isopods vary from facultative associates, which cohabit with ants only occasionally and are represented by many records, to obligate guests that live permanently within ant nests. These obligate guests thrive in ant fortresses by specific behavioural, chemical and morphological adaptations. Their effect on the host can range from negative to neutral, or potentially even beneficial. Though modest in number, with 23 species across 10 genera, the diversity of obligate myrmecophilous isopods showcases a fascinating pattern of independent evolution in soil ecosystems.