Building a polydomous colony: nest network expansion by Linepithema humile

Abstract A number of ant species are polydomous, where the members of the colony reside in multiple nests rather than all inhabiting one central location. Polydomous nests have interconnected trail systems and individual ants can freely exchange between sites. This appears to spatially distribute workers in ways that create advantages for encountering, defending and exploiting food resources. Indeed, many successfully invasive ant species exhibit polydomy to the extent that, as evidenced in the Argentine ant ( Linepithema humile ), introduced propagules can grow into supercolonies of enormous size that displace or eradicate the formerly-present native species. This study examines how initial single nests of L. humile expand into building polydomous networks. Key findings are that: 1) Expansion to a relatively stable distribution occurs rapidly over the course of 5–10 days; 2) Expansion favors areas that are more rewarding in food than water; 3) Expansion, however, does not completely saturate all available sites, including some that contain food or water; 4) Some queens and brood do migrate out of the central location, but most of the expansion sites contain only workers; and 5) Queen and brood relocations do not always minimize distance to either food or water. The results are suggestive that for L. humile the edges of their polydomic aggregations serve to increase foraging and territory defense success rather than brood rearing. The consistent lack of total habitat saturation further suggests that colony-level satiation acts as a brake on nest-site expansion and may leave areas open for use by other species.