Ant nests are one of a number of key characteristics of an ant colony that are of primary importance in defining an ant species' basic biology and life history. Some of this is brought out in the study that follows by Zakharov (2015) about the classification of nest complexes.
A study by Goryunov (2015) of nest building in Formica exsecta provides a detailed examination of how that species forms and maintains its nests.
Classification of Ant Nest Complexes
Zakharov (2015) provided details regarding how ant nests are begun, grow and are maintained.
Ants, as eusocial insects, possess specific ways of development of population structures related to their ability for sociotomy and formation of temporary and permanent structures above the colony level. The self-development of ant settlements leads to establishment of vast territorial systems, namely, complexes of ant nests consisting of tens and hundreds of interacting colonies. The ant nest complex is a system of conspecific ant nests whose adjacent foraging areas form a territorial continuum.
The complex is the principal biochorological phenomenon at the population level in ants. Its size, structure, and configuration reflect the results of historical development of the ant settlement in its interaction with the topical, geographic, and synecological factors. The complex is the main scene of intrapopulation events in ants, since within it the main migration events take place, the processes of self-organization (establishment and optimization of the functional and chorological structures) are realized, the main exchange of genetic material occurs, the population density is optimized, and the settlement is restored and restructured under critical conditions. Under favorable conditions, dispersal of ants over the available habitats leads to structuring of the complex, with formation of subcomplexes within it or with separation of a part of the settlement as a secondary complex. In fact, the spatially isolated complex (or a group of nest complexes of the same species) is the local population, or metacomplex.
The ant nest complex is a self-developing system of conspecific nests interacting in certain ways, which may exist for decades and has a history of its own. Its life, similar to the life of an individual ant nest, includes the stages of growth, stabilization, depopulation, and degradation. The potential life span of the complex considerably exceeds that of an individual nest, and is mostly determined by its size and level of structuring. Complexes may vary in the total number of ants and the size, age, state, density, and the level of organization of the nests included in them. A complex may consist only of single young nests, of nest coalitions, or only of old, declining nests.
The Modal Scenario of Formation and Staged Development of an Ant Settlement
The development of each settlement includes up to 5–6 distinct stages that differ in the characteristics of the elements (ant nests) composing the settlement, the level of integrity and the system of connections between them, the specific traits of territory use, and other aspects (Goryunov, 2007; Zakharov, 2013). They include the consecutive modal stages of the life of the ant settlement and the development of the complex established in it: procomplex, mesocomplex, and hypercomplex.
The zero point should always correspond to the time of foundation of the primary nest. This nest can be founded in three ways:
- Founding of the new colony by a single queen (the foundress)
- Pleometrosis, which herein means only the joint founding of the new nest by several young mated queens
- Temporary social parasitism
Only the complexes formed in these ways may be considered as primary ones. All the other settlements formed by sociotomy, migrations or recolonization from refugia should be regarded as secondary; their stages of development can still be assessed in the framework of the general system, but the approaches related to the colony cycle theory (Starr, 2006) cannot be fully applied to secondary settlements.
Ideally, we would consider an even-aged monocentric complex developing from a single center (from one primary nest). However, this situation is very rare, and in reality we nearly always deal with settlements formed from several centers. In addition, as the result of many years of dispersal, the advanced center of a monocentric settlement becomes surrounded with concentric zones showing some earlier stages of development of the given complex (e.g., see Stukalyuk, 2013). In the polycentric variant, the complex acquires a mosaic structure due to the formation of subcomplexes within it, which may be at different stages of development (Zakharov and Kalinin, 2007).
Stage 0. The primary settlement in a new place is started with the founding of the primary nest, either by a single queen, several queens, or via temporary social parasitism. The primary nest grows and becomes ready to produce secondary nests.
Stage 1. Polycalic systems and/or temporary supracolonial structures appear; the number of nests grows but the nests remain dissociated and do not yet form a territorial continuum.
At the first two stages, there is still no complex, because not any group of ant nests but only a group with a high level of internal relations may be regarded as a complex (Alaev, 1983). Unification of the elements of ant settlements within a single territorial continuum may be considered an indicator of establishment of real and stable interrelations between them. In ecosystem morphometry, these events may be described in terms of consolidation and compartmentalization (Vinogradov, 1998).
Stage 2. Protocomplex: the stage of extensive development. The density of the settlement increases, and the territorial continuum is established, still at a low level of territory structuring and a relatively small size of the nests.
Stage 3. Mesocomplex: the stage of intensive development and structuring of the settlement. The degree of differentiation of the elements by size and function increases, as does the integrity of the complex. The territories of ant colonies become structured and able to support high population density and large nests. Permanent supracolonial structures start to appear.
Stage 3a. Stabilization of the mesocomplex: the stage of leveling of the nests by size and gradual decline of the dispersal activity. Large complexes may experience depression-restoration waves at this stage.
Stage 4. Hypercomplex: polymerization (Zakharov, 1991), i.e., integration of ant nests into a secondary federation or the formation of several interconnected nest aggregations in case of a primary federation. The hypercomplex is characterized by the highest levels of abundance, population density, integrity, self-regulation, and stability possible for the given species.
The ant settlement may stop at any of the intermediate stages (0–3) of its development and try to stabilize itself. The new community has no chance of being preserved at stage 0; however, this chance appears at a certain level of settlement development and increases from stage 1 to stage 3 (Zakharov, 2011).
The Key Features of an Ant Species
In this work, the key species-specific features refer to those traits which are of crucial significance for the existence and development of the ant community. Such features include:
- the basic level of intracolonial structures (clan, column, pleiad)
- the nest type (sectional or capsule-like)
- the modes of nest founding (haplometrosis, pleometrosis, temporary social parasitism)
- the modes of dispersal sociotomy (binary division, budding, fragmentation)
- the definitive colony size (Nc)
- the presence of a defended territory
- the form of polycaly (PC0, PC1, PC2, PSN)
- the spatial configuration of the settlement
- the type of permanent supracolonial structures (the metastable states possible for the given species: MSS-0 – MSS-3).
The number of queens and the key events in the life of an ant nest. It is essential for development of the settlement infrastructure that realization of specific structural variants may be blocked by some features or their combinations. One of the most important features is the number of egg-producing queens.
The number of queens in the colony is a crucial factor in the life of ant communities. Its changes considerably affect the organization of each individual nest and the local populations to which these nests belong. This problem has different aspects. Indeed, on the one hand, the number of queens is believed to determine the main traits of the social organization of ants (Bourke and Franks, 1995; Keller, 1995). On the other hand, the number of queens in nests of the same ant species may change within a broad range (from one to several hundreds), depending both on the stage of the colony development (Pisarski, 1982) and on the phase of its annual cycle, as this was demonstrated, for example, in Linepithema humile. In addition, the number of queens varies depending on the living conditions of ants in different parts of their range (Bourke and Franks, 1995; Bondar and Rusina, 2003) and in different biotopes (McGlynn, 2010). Transition from monogyny to polygyny may accompany the northward expansion of a species (Henze and Hölldobler, 1994) or its introduction into new regions (Tsutsui and Suarez, 2003).
The above examples show that the number of queens is as variable as most other parameters of the ant community. It may change depending on the size and age of the colony, climatic and topical conditions, nest design, population density, ecological factors, etc. There are some parameters of the ant nest which are undoubtedly related to the number of queens. Polygyny increases the total reproductive potential of the colony and reduces its vulnerability (Starr, 2006). It also stimulates the development of subordination systems, thus removing the restrictions on the size of individual structures (Zakharov, 1991). Besides, polygyny ensures a higher level of heterogeneity, phenotypic diversity, and tolerance of ants, opening the way to formation of vast interrelated settlements (Crozier and Pamilo, 1996).
At the same time, the number of queens by itself does not limit any of the key functions of the ant community (Bourke and Franks, 1995; Zakharov, 2011). Both variants (monogyny and polygyny) permit the following events: (a) formation of new colonies by young mated queens (on their own or using the mechanism of temporary social parasitism); (b) the use of auxiliary nests, with transition to polycaly; (c) sociotomy; (d) formation of permanent supracolonial structures. However, each of these events follows considerably different scenarios in the monogynous and polygynous species.
(a) Polygynous species of the temperate zone more often pass through the phase of temporary social parasitism during colony founding, whereas independent founding is more typical of monogynous species. However, independent founding is often pleometrotic in both variants.
(b) Auxiliary nests can be built by all the ant species which have colonies so large as to make the use of such nests expedient. The threshold colony size is species-specific and related to other parameters of the ant communities and their living conditions (Zakharov, 2005).
(c) Colony budding in polygynous species involves the queens already present in the nest, whereas the new nests of monogynous species adopt queens from the original nest prior to budding or even after it (Schneirla, 1971; Dlussky, 1981; Bourke and Franks, 1995).
(d) During the establishment of secondary federations, polygynous species inhabiting large nests usually build special buffer nests between them, whereas in monogynous species the buffer function is performed by the auxiliary nests of polycalic systems.
Similar to the above, the mode of colony founding (haplometrosis, pleometrosis or temporary social parasitism) does not place any limitations, either (Zakharov, 2011). However, this mode determines the behavior of ants at the bifurcation points, namely, their choice between monogyny and polygyny (Batz and Hölldobler, 1982; Pisarski, 1982; Rissing and Pollock, 1988; Zakharov, 2011).
The Social Types
The form of organization of the ant settlement results from interaction of many features characterizing a particular species or population. Despite the great number of possible combinations of features, they can be realized in a fairly limited set of forms of settlement organization, which are common to different taxa of ants and even other eusocial insects. The limited number of these variants is largely determined by the limited number of variants of social structures (Zakharov, 1991, 2013).
Based on the key features and scenarios of development of settlements of 120 ant species, it was possible to distinguish eight principal social types, which were named by their essential traits (Table 1):
- Recurrent sociotomy based on a clan
- Diffuse polycaly
- Recurrent sociotomy based on a single colony
- Cosed (ordinary) polycaly
- Open (obligate) polycaly
- Linear settlements
- Dissipated pleiads
- Unitary pleiads
The definitions of these social types and their model species are given below.
Social type 1. Recurrent sociotomy based on a clan: a simple, spontaneously developing settlement. A simple complex of solitary nests is formed within a small optimal area. The structural level of the colony is that of a clan. The definitive colony size is Nc = 3 × 102–1 × 103. The colonies are monogynous, founded independently by single queens. The mode of sociotomy is binary division with fast separation of the secondary nests, by which the colonies return to their basic structural level (Soans and Soans, 1971). The nests are sectional and shallow. The colony has no defended territory.
Social type 2. Diffuse polycaly, at which the colony preserves its integrity but occupies several temporary nests without permanent residents. Ants move constantly from one nest to another, nests are often replaced with new ones, and the total number of nests in the system varies (Creighton, 1963; Zakharov, 1991). However, such a system is stable, and its internal flexibility allows the total colony to include as many as 2 thousand individuals. Sociotomy proceeds by fragmentation. The colony has no defended territory.
- Model species: Pseudoponera stigma, Rhytidoponera metallica, Rhytidoponera terros, Anochetus sp., and Cephalotes texanus.
Social type 3. Recurrent sociotomy based on a single colony: a simple, spontaneously developing settlement. Under optimum conditions, complexes of solitary nests are formed in small areas, with simple polycaly (PC1) at the utmost. The structural level is that of a single colony. Nc = 3 × 103–5 × 104. Monogyny → polygyny. Colonies are founded independently by single queens. Sociotomy proceeds by binary division leading to the formation of an ephemeral coalition (Wehner and Lutz, 1969; Zakharov, 1991), after which separation of the secondary nests returns the secondary colonies to the basic structural level. The nests are sectional and capsule-like. The defended territory is absent or partial.
Social type 4. Closed (ordinary) polycaly: a compound complex of small monocalic and polycalic (PC2) nests practically not reaching the level of supracolonial structures. The structural level is that of a single colony. Nc = 1 × 103–5 × 104. The colonies are monogynous, less frequently polygynous; they are founded independently by single queens and exist for a time comparable to the queen’s life span (Bourke and Franks, 1995). The development of polycaly is largely determined by external (topical) conditions. The nests are sectional and capsule-like. The defended territory is absent or partial.
- Model species: Formica rufibarbis, Dolichoderus quadripunctatus, Messor aralocaspius, Messor variabilis, Monomorium kusnezowi, and Manica rubida. Some model species are temporary social parasites: Formica forsslundi (on Formica picea), Lasius mixtus (on Lasius s. str.).
Social type 5. Open (obligate) polycaly PC2; adopters: a compound complex consistently passing through several (4) stages of development with increasing integrity and differentiation of elements by size and functions. The main system of connections is radial or (in case of PF1) netlike. The structural level is that of a single colony, developing into PC2; coalitions of columns are possible. Nc = 5 × 104–5 × 105. Variants: (5A) pleometrosis with facultative transition to primary polygyny; (5B) temporary social parasitism with obligatory transition from monogyny (with a tendency for physogastry) to secondary polygyny. The development of polycaly is largely determined by endogenous conditions. Sociotomy proceeds by budding with adopting of gynes (Reznikova, 1983). In case of overpopulation, PC2 form a secondary federation SF1 (Zakharov, 1991). The nests are sectional and capsule-like. The colony has a defended territory.
- Model species: (5A) Liometopum microcephalum, Camponotus herculeanus, Lasius flavus, Lasius niger, Crematogaster sorokini, and Crematogaster subdentata; (5B) Formica pratensis and Lasius fuliginosus.
Social type 6. Linear settlements: a compound complex consistently passing through the following stages: monocaly → simple polycaly (PC1) → polycaly with breeding nests (PC2) → primary federation (PF). The prevalent configuration is linear; PF has a relay-netlike system of connections. The territory is typically subdivided into the nesting zones, containing nest aggregations, and the foraging zones. The structural level is that of a single colony, developing through polycaly with breeding nests (PC2) into a primary federation (Goryunov, 2007). Nc = 3 × 104–1 × 106. Variants: (6A) pleometrosis with facultative transition to primary polygyny; (6B) temporary social parasitism with obligatory transition from monogyny to secondary polygyny. Sociotomy proceeds by budding and by regular (coordinated with the annual cycle) fragmentation and reintegration. The nests are sectional and capsule-like. The entire territory of large nests and federations is defended.
- Model species: (6A) Formica cinerea and Iridomyrmex purpureus; (6B) Formica exsecta and Formica pressilabris.
Social type 7. Dissipated pleiads: a compound complex developing in stages with increasing integrity of the stereotyped elements. The main system of connections is radial or (in SF2) netlike. The basic structural level is that of a pleiad inhabiting a polysectional nest. Nc = 5 × 103–1 × 105. Pleometrosis with transition to primary polygyny and dispersal of queens over the section of one nest. Sociotomy proceeds by binary division inside the polysectional nest. Fragmentation of large colonies is possible. Overpopulation may lead to the development of a secondary federation SF2 (Mizutani, 1981; Zakharov and Fedoseeva, 2005). The nests are either sectional or of two types: sectional and capsule-like. The defended territory may be common or partial.
- Model species: Tetramorium caespitum, Tetramorium schneideri, Pheidole pallidula, Messor laboriosus, Myrmica rubra, Tapinoma karavaievi, Formica fusca, Formica cunicularia, and Cataglyphis aenescens.
Social type 8. Unitary pleiads: a compound complex developing in stages with increasing integrity and complexity of its elements. The main system of connections is radial or (in SF2) netlike. The basic structural level is that of a pleiad inhabiting a polysectional nest. Nc = 1 × 105–1 × 107. Variants: (8A) pleometrosis with transition to primary polygyny; (8B) temporary social parasitism with transition from monogyny to secondary polygyny. Sociotomy proceeds by binary division (inside the colony) and budding. Overpopulation leads to SF2 (Zakharov, 1994). The nests are capsule-like. The colony has a common defended territory.
- Goryunov, D. N. 2015. Nest building in Formica exsecta ants (Hymenoptera, Formicidae). Zoologichesky Zhurnal. 94:1132-1137. doi:10.1134/S0013873815080035
- Zakharov, A. A. 2015. Classification of ant nest complexes. Entomological Review. 95:959-971. doi:10.1134/s0013873815080047