Xenobiosis

Xenobiosis, also referred to as compound nests or guest ants, occurs when two species of ants live together in the same nest but keep their broods separate and they show minimal actual interaction with each other. Details of the relationship among the partners in a xenobiotic nest vary considerably. In some cases, the species involved are essentially equal partners with little indication of either species being a "guest" or a "host" (parabiosis and plesiobiosis). In other cases, the guest species form small colonies (up to a hundred individuals) in the nesting material or nest walls of the host and are normally much smaller than their host (cleptobiosis and lestobiosis). The guest maintains its nest well separated from the brood chambers of their host and they tend their own brood. They are dependent upon the hosts for nutrition and often shelter and some xenobiotic species may solicit regurgitated food directly from a host worker or participate in food exchange (trophallaxis) between two host workers.

The biology of Formicoxenus nitidulus provides natural history information about one representative guest ant.

Xenobiotic species generally fall into one of 4 subtypes:
 * Cleptobiosis: stealing food from other species; a mutual relation in which members of one species habitually steal food from another.
 * Lestobiosis: stealing brood; cleptobiosis in which covert thievery replaces aggressive plundering.
 * Parabiosis: sharing nests and trails.
 * Plesiobiosis: casual or regular nesting in close vicinity; casual association of two or more colonies.

Plesiobiosis
Kanizsai et al. (2013) - Plesiobiosis, the most basic form of interspecific associations in ants, denotes occasional or regular nesting of heterospecific colonies of certain species pairs in close proximity to each other without biological interdependence. Plesiobionts differ from each other both in morphology and in behaviour (e.g., in their foraging strategies), and at least one of the plesiobiotic pair is a submissive species. Recent studies on plesiobiosis have revealed that Formica fusca and Lasius flavus are two of the most frequent plesiobionts. To date, at least 48 different plesiobiotic species pairs have been recorded from various habitat types of the Holarctic region. Two main habitat properties may play a role in the forming of plesiobiosis: the scarcity of suitable nesting sites as a forcing factor and the suffcient amount of food sources available, influencing the abundance of colonies. Thus, high colony density may contribute to the formation of such associations, resulting in (1) frequent nesting in each other’s neighbourhood and (2) stronger intraspecific competition, which forces colonies into the vicinity of heterospecific nests. Plesiobiotic associations formed this way may promote persistent coexistence, leading to the formation of other types of interspecific associations (e.g., clepto- or lestobiosis).