Social Parasitism

Social parasitism is the coexistence of two or more ant species in one nest or colony. It involves a parasitic species which is dependent on one or several host species. The relationship can be obligatory or facultative, permanent or temporary. These relationships can take many forms and have been classified in various ways.

Holldobler & Wilson (1990), following a suggestion of Wasmann (1891), distinguished between "compound nests" and "mixed colonies".
 * Compound nests (xenobiosis) involve two species of ants living together in the same nest but keeping their broods separate. One species lives in the walls or chambers of the nests of the other and moves freely among its hosts, obtaining food from them by one means or another, usually by soliciting regurgitation. The details of specific relationships vary with the species involved, and can broadly be classified into a series of essentially continuous types.
 * Plesiobiosis. In this most rudimentary association, different ant species nest very close to each other, but engage in little or no direct communication.
 * Cleptobiosis. Some species of small ants build nests near those of larger species and either feed on refuse in the host kitchen middens or rob the host workers when they return home carrying food.
 * Lestobiosis. Certain small species, most belonging to Solenopsis and related genera, stay in the walls of large nests built by other ants or termites and enter the nest chambers of their hosts to steal food and prey on the inhabitants.
 * Parabiosis. In this peculiar form of symbiosis, two or more species use the same nest and sometimes even the same odour trails, but they keep their brood separate.
 * Mixed colonies comprise temporary parasites, slave-makers (dulosis) and inquilines, where the host workers care for the parasite brood, at least temporarily.

As an alternative, Buschinger (2009), in his review of social parasitism, proposed the following classification: "Obligatory slavemakers" are completely and permanently dependent on regular replenishment of their slave stock by raiding host species colonies. The term "degenerate slavemaker" has been coined for species that belong to a monophylum of obligatory slavemaking species but have secondarily abandoned the slavemaker worker caste, or reduced its number, hence can‘t conduct slave raids. Examples are Temnothorax kraussei (reduced slavemaker workers to a few, or zero), Temnothorax corsicus and Temnothorax adlerzi (both workerless; all three belong to former genus Myrmoxenus), and Temnothorax brunneus (workerless, former genus Chalepoxenus). The distinction is necessary since the queens of the degenerate slavemakers have retained the colony foundating behavior of their actively dulotic relatives, i.e. kill the host coloy queen by throttling her to death (former Myrmoxenus) or stinging (former Chalepoxenus). This is different from workerless inquilines whose queens live in queenright host species colonies, and who most probably derive directly from an independent species (example Leptothorax kutteri and Leptothorax pacis with Leptothorax acervorum as host species).
 * Xenobiosis (guest ants, sometimes called cleptobiosis or kleptobiosis) - The biology of Formicoxenus nitidulus provides natural history information about one representative guest ant.
 * Temporary parasitism (occurring together only during colony foundation) - The biology of Lasius umbratus provides natural history information about one representative temporarily parasitic ant.
 * Permanent parasitism with slavery (dulosis) - The biology of Temnothorax muellerianus and Polyergus rufescens provide representative accounts of dulosis. Note that slave-making species range from being largely self-sufficient and easily able to survive without the support of slaves (facultative dulosis, as in Formica sanguinea), to having a very limited behavioral repertory and apparently completely helpless without their slaves (referred to as degenerate slavemakers) (Holldobler & Wilson, 1990).
 * Permanent parasitism without slavery (inquilinism) - The biology of Tetramorium inquilinum (as Teleutomyrmex schneideri) provides natural history information about one representative inquiline ant.

Parasite Evolution
Understanding how ants evolved to be parasites of other ants is an important, long-standing question.Hölldoble rand Wilson (1990) stated the following "Social parasitism in ants is complicated . . . the source of the complexity is first the large number of ant species that have entered into some form of parasitic relationship with each other. Second, at least two and possibly three major evolutionary routes lead to the ultimate stage of permanent, workerless parasitism. Finally, no two species are exactly alike in the details of their parasitic adaptation."

This section needs to be expanded!

Chemical Deception Among Social Parasites
Guillem et al. (2014) examined cuticular hydrocarbon (CHC) profiles among the parasites Camponotus universitatis, Harpagoxenus sublaevis‎‎ and Strongylognathus testaceus and their hosts. They found that the parasitic species had CHC profiles that were indistinguishable from that of their hosts, even when the parasite is using more than one host species. The level of chemical mimicry even extended to the more subtle between-colony differences in profiles. In all cases the profiles of un-parasitized colonies were similar to those that were parasitized indicating that it is the parasites that have adjusted their profile to match that of their host and not vice versa. This explains why these social parasites are fully integrated members of each colony and are treated as nest-mates.

They also noted that in some species, for example Harpagoxenus sublaevis (Winter and Buschinger, 1986), raiding workers are frequently killed or driven off when trying to raid or invade new host colonies, since they are carrying their own host colony odour, which is likely to be different from that of the one they are raiding. This is why parasites continue to use a wide range of other chemical and morphological adaptations associated with their parasitic lifestyle. These include a thickened cuticle and production of appeasement or propaganda compounds (e.g. Allies et al., 1986; Lloyd et al., 1986; Ollett et al., 1987; D'Ettorre et al., 2000). These tactics allow the parasite time to make the necessary adjustments to its profile. Acquiring a host profile may be possible in just a few hours (R. Kather, pers. comm., cited in Guillem et al. (2014)).

Parasitic Ant Species
This information has been modified from Buschinger (2009). Please cite the original publication as the source for these data.

dDul = degenerate dulosis; Dul = dulosis, slave-maker; In = inquilinism; Tp = temporary parasitism; Xen = xenobiosis, guest ant.