Morphological characteristics reflect food sources and degree of host ant specificity in four Myrmecophilus crickets

Myrmecophilus crickets are well-known inquilines that live and obtain food resources in ant nests. In Japanese Myrmecophilus species various degrees of host specificity are reflected in behavioral differences among species. For example, extremely specialized species perform trophallaxis with their host ant species, whereas generalist species may steal food from their hosts without any intimate contact. We examined behavioral variations among four Myrmecophilus species that use different hosts and show different degrees of specificity, and we also compared morphological traits such as mandible shape and hind leg length among the species. The morphometric analyses showed that an extreme host-specialist species had less complex and largely non-functional mandibles, reflecting its dependence on trophallaxis with its host ant species. In contrast, extreme host-generalist and/or moderate specialist species, which directly eat solid foods, had more complex and functional mandibles which they use to cut and crush their foods, such as insect carcasses and ant larvae. The extreme host-specialist species had shorter hind legs than the extreme host-generalist. This may reflect that it suffers few attacks from the host ants. Our results show that in Myrmecophilus food sources shape behavioral interactions with host ant species and correlate with morphological characteristics.