Myrmecophiles

How diverse are myrmecophiles? In 1894, Erich Wasmann, an Austrian Jesuit priest and one of the pioneering students of myrmecophiles, documented 1,177 ant guests, and the list has grown at an astonishing rate ever since. Myrmecophily has evolved independently in a large number of taxonomic groups, including flies (Figure 1A), beetles (Figure 1B and C), crickets (Figure 1D), butterflies (Figure 1E), bristletails, millipedes, isopods, snails, mites, aphids, scale insects, wasps, and even snakes. The taxonomically most diverse groups of myrmecophiles are mites and staphylinid beetles. Ant species with the largest colonies generally harbor the highest diversity of myrmecophiles, while most species with small colonies rarely entertain guests. The reasons for this pattern are similar to those governing the dynamics of island biogeography: large colonies provide a larger variety of microhabitats and can sustain larger and more stable populations of guests over longer time periods. A particularly striking diversity of myrmecophiles is associated with army ants (Figure 1A–C). Colonies of army ants contain between tens of thousands and millions of workers, which form large raiding parties that overwhelm and kill other arthropods. In a recent overview, Rettenmeyer et al. (2010) listed over 300 animals that depend on a single army ant species, Eciton burchellii. Most of these species are inquilines, including mites, beetles, scuttle flies, and bristletails. Army ant myrmecophiles are not only extremely diverse taxonomically, they are also abundant. One study estimated that an average Eciton burchellii colony harbors 20,000 mites. The nomadic colonies of army ants really are travelling circuses.