The allocation of foragers in red wood ants

Abstract. 1. We studied how colonies of the red wood ant, Formica polyctena , adjust the numbers of foragers allocated to different foraging trails. In a series of field experiments, foragers were marked and transferred from one nest to another, related nest, where they joined the foraging force. Transferred workers acted as a reserve of uncommitted, available foragers.
2. Previous work shows that each individual forager habitually uses one trail. We found that for an uncommitted forager, the influence of recruitment initially is stronger than that of directional fidelity. Transferred workers were likely to use trails leading to new food sources. When transferred to a new nest, foragers were not likely to use a trail in the same direction as their original trail in the donor nest.
3. After a week, transferred foragers tended to develop route fidelity. Even after bait was no longer present, they continued to use the trail that had formerly led to a bait source.
4. We examined how colonies adjust numbers on a trail by experimentally depleting some trails. Colonies usually did not compensate for depletion: foragers were not recruited to depleted trails.
5. In general, the dynamics of foraging in this species facilitate a consistent foraging effort rather than rapid adjustments of forager allocation.     

An innate template for enemy recognition in red wood ants

The hypothesis of the innate template for perception and recognition of the enemy image in red wood ants Formica aquilonia Yarr. was tested by initiating conflicts between ants and predatory ground beetles, their competitors for space. Live beetles and their models with different characters were used. In nature, ants respond selectively to such features of competitors as dark coloration, the presence of “outgrowths” (legs, antennae), body symmetry, the rate of movement, and scent. Comparison of behavior of ants from natural colonies and “naive” (laboratory reared) ones showed that ants having no experience of encounters with competitors responded aggressively to an integral and sufficiently realistic enemy image. This suggests that red wood ants possess an innate template for recognition of potential competitors. At the same time, the ability to single out the key features and complete the integral image seems to require accumulation of experience.     

Spatial distribution of red wood ants and scientific basis of their protection

The results of long-term research on spatial distribution of red wood ants in the Urals and Western Siberia are presented. It was shown that large complexes counting tens and hundreds of nests clearly tended to form aggregations, or zones of high density. These zones are extended latitudinally and arranged in a striate pattern, with stripes about 15 km wide, about 100 km long, and positioned 100–120 km apart. The possibility of using these trends for the protection of red wood ants and for future research is discussed.     

Molecular markers allow sibling species identification in red wood ants (Formica rufa group)

Red wood ants (Formica rufa group) constitute a group of species that are considered to be among the most promising bioindicators in forest ecosystems. However, because of their morphological similarity and intraspecific variability, morphological species identification can be difficult. Considerable expertise is necessary to discriminate between the sibling species F. lugubris and F. paralugubris, two species that often live in sympatry in the same Alpine forests. New taxonomic tools providing rapid and reliable species identification are needed. We present a simple and reliable molecular technique based on mtDNA (COI gene) and a restriction enzyme for discriminating between F. lugubris and F. paralugubris. We confirm the validity of this method with a Bayesian analysis based on microsatellites. This new molecular tool represents a clear breakthrough for discriminating between F. lugubris and F. paralugubris and is likely to be helpful in large‐scale biomonitoring.     

Immigration and formation of mixed colonies in red wood ants (Hymenoptera,Formicidae)

Long-term field studies of the composition and spatial structure of settlements of ants of the Formica rufa group were carried out in two regions of Russia (Moscow and Arkhangelsk provinces). Fragmentation of damaged nests followed by reintegration of the fragments is the main way of formation of mixed colonies of ants from different nests (including different species). The principal factor of nest fragmentation is their damage by wild boars, bears, and in some localities, by poachers. The formation of mixed nests and nest complexes with participation of different Formica species was observed. They are formed by joining the ants from several damaged nests or by a colony from a destroyed nest immigrating into an intact one. Regular damage of many nests leads to the formation of broad zones of mixed colonies. The mixed colonies including 2–3 species of wood ants have recently become common. The phenomenon of mixed colonies raises a question as to the relative importance of two basic principles (sociality and specific identity) in the life of ant societies and demonstrates the priority of the social principle.     

Field tests of interspecific competition in ant assemblages: revisiting the dominant red wood ants

1. There has been considerable debate on the importance of competition in ecological communities, but its importance in structuring ant assemblages has often been uncritically accepted. Here, we briefly review field experiments examining competition in ant assemblages and use a removal experiment to test the effect of the classical territorial dominant ant, Formica aquilonia. Ants of this species group are thought to structure communities through a dominance hierarchy. 2. First, we used pitfall traps to compare the abundance of other ants in replicated sites with low and high densities of F. aquilonia. We found differences in community composition, in particular, Camponotus herculeanus was more common in low-density sites, in accordance with predictions. Differences in ant assemblages were not owing to differences in measured habitat variables. 3. We removed F. aquilonia from a set of high-density sites, using physical and chemical methods, and repeated these procedures at procedural control sites. One year after removal, abundances of F. aquilonia at removal sites were similar to those at low-density sites. However, the composition of other species did not change in response to F. aquilonia removal. Replication rates were identical in the mensurative and experimental components of this study, so this is unlikely to be owing to the analysis being insufficiently powerful. 4. We suggest three possibilities for the lack of difference. First, the study may have been too short term or small scale to detect differences. However, previous studies have shown effects on smaller spatial- and temporal-scales. Second, priority effects may be important in the successful colonisation by F. aquilonia. Thirdly, boreal ant assemblages may be too depauperate for redundancy in ecological roles and for competition to play an important structuring role. 5. We thus recommend that long-term large-scale experiments be considered essential if we are to distinguish between competing hypotheses in community ecology.     

Are red wood ants (Formica rufa-group) tectonic indicators? A statistical approach

Recent research in seismically active areas indicated that the spatial distributions of geochemical soil gas anomalies and nests of red wood ants (RWA; Formica rufa-group) are strongly correlated. Here we applied a modified Hough Transform (mHT) and an Iterative Mode Detection (IMD) to RWA nest positions, which we mapped in two Southwest German study areas (Black Forest and Bodanrück), to test for statistical significance of correlation with tectonic features. RWA densities in the seismically active study areas reaching up to 1600 nests/100 ha are about 100× higher than overall values for Northern and Southern Germany. Since the shape of edges of the study area was found to strongly influence the selection of distribution patterns, all subsequent analyses were carried out for circular study areas. Results of the mHT applied on the RWA nests in both study areas clearly showed several modes which correspond to preferred directions. Centres of the modes further processed by IMD transferred into a GIS as RWA prototype lines showed very dominant directions of RWA nest distributions in right lateral strike-slip mode in WNW-ESE resp. NW-SE direction but also in extension direction caused by the recent main stress field in NW-SE resp. NNW-SSE direction. It could thus be clearly shown that the large scale spatial distribution of RWA nests directly reflects significant components of the present day stress field and its accompanying conjugated shear systems: Linear alignments of RWA nests indicate the course of active degassing faults zones and nest clusters indicate area-wide geochemical anomalies respectively crosscut zones of different fault systems. Furthermore, directions of re-activated shear systems, e.g. from Eocene-Oligocene but also from Late Jurassic that had been modified by overprinting due to changes of the main stress field could be identified. Therefore, RWA prototype lines complement and clarify the shear sense and the tectonic regime identified in previous tectonic studies. The high degree of statistical significance of these results will also allow a rating with former contrasting interpretations as to the drivers of RWA distributions.     

Wood ants are wood ants: deforestation causes population declines in the polydomous wood ant Formica aquilonia

Abstract.  1. One of the main themes in ecology is adaptation for survival in different habitats and the potential of the environment to regulate populations.
2. The effects of clear-cutting on nest-abandonment rate and local population sizes in the polydomous wood ant Formica aquilonia was studied, using uncut forest stands as controls.
3. The nest-abandonment rate was clearly higher in clear-cuts than in forest interiors. In clear-cuts, 39% of pre-deforestation nests and 73% of new bud-nests were abandoned 4–5 years after deforestation, whereas in forest interiors fewer than 2% of nests were abandoned at the same time period. Local population size decreased 30% in clear-cuts, but fewer than 2% in forest interiors.
4. The results demonstrate that despite modern logging practices in which mechanical harming of nest mounds is reduced, nest mounds are abandoned at high rate, and despite frequent establishment of new bud-nests, populations start to decline.
5. The likely reason for the high nest-abandonment rate in clear-cuts is a combination of changed abiotic conditions, resource limitation, and disturbed reproduction.
6. Species that are sensitive to changes in the size of habitat patch, such as F. aquilonia , likely are harmed by logging, even employing biodiversity oriented management practices. Hence there is a need for conservation actions that are based on the size of protection areas.     

Forestry alters foraging efficiency and crop contents of aphid-tending red wood ants, Formica aquilonia

Forest management alters species behaviours, distributions and interactions. To evaluate forestry effects on ant foraging performance, we compared the quality and quantity of honeydew harvested by ants among clear-cuts, middle-aged and mature spruce-dominated stands in boreal forests in Sweden. Honeydew quality was examined using honeydew collected by squeezing the gasters of laden Formica aquilonia workers. We used fifteen laden individuals at each study site (four replicates of each stand age) and analysed honeydew chemical composition with gas chromatography-mass spectroscopy. To compare the quantity of honeydew collected by individual ants, we collected and weighed five ants moving up and five ants moving down each of ten trees at the twelve sites (totally 1200 ants). The concentration of trehalose in honeydew was lower in clear-cuts compared with middle aged and mature stands, and similar trends were shown for sucrose, raffinose and melezitose, indicating poorer honeydew quality on clear cuts. Concentrations of the amino acid serine were higher on clear-cuts. The same trend occurred for glutamine, suggesting that increased N-uptake by the trees after clear cutting is reflected in the honeydew of aphids. Ants in mature stands had larger heads and carried proportionally more honeydew and may therefore be more efficient foragers. Human alternation of habitats through clear-cutting thus affects food quality and worker condition in F. aquilonia. This is the first study to show that honeydew quality is affected by anthropogenic disturbances, likely contributing to the reduction in size and abundance of F. aquilonia workers and mounds after clear cutting.     

An experimental study of behavioral mechanisms of relationships between red wood ants and ground beetles

Behavioral mechanisms regulating the competitive relations between the red wood ant Formica aquilonia and the ground beetles Carabus regalis, Pterostichus melanarius, P. magus, P. oblongopunctatus, Harpalus smaragdinus, and Amara nitida were studied by artificially initiated collisions between living insects as well as with the use of imitation models. Members of different functional groups within an ant family (aphid-milkers, hunters, and guards) behaved differently towards beetles. Active ants were shown to respond selectively to different features of the possible competitors, such as coloration, the presence of “appendages” (legs, antennae), body symmetry, rate of movement, and scent. Field and laboratory experiments demonstrated the ability of beetles to avoid collisions with active ants. The scent of anthill material attracted ground beetles, which consumed dead ants. The gained individual experience may allow the beetles to use supplementary forage resources in the territories controlled by ants. The flexible tactical patterns facilitate spatial segregation of ground beetles and ants in the same territory and result in a more complete utilization of food resources.     

Nest mounds of red wood ants (Formicaaquilonia): hot spots for litter-dwelling earthworms

A previously undocumented association between earthworms and red wood ants (Formicaaquilonia Yarr.) was found during an investigation of the influence of wood ants on the distribution and abundance of soil animals in boreal forest soil. Ant nest mounds and the surrounding soil of the ant territories were sampled. The ant nest mound surface (the uppermost 5-cm layer) harboured a much more abundant earthworm community than the surrounding soil; the biomass of the earthworms was about 7 times higher in the nests than in the soil. Dendrodrilusrubidus dominated the earthworm community in the nests, while in soils Dendrobaenaoctaedra was more abundant. Favorable temperature, moisture and pH (Ca content), together with abundant food supply (microbes and decomposing litter) are likely to make a nest mound a preferred habitat for earthworms, provided that they are not preyed upon by the ants. We also conducted laboratory experiments to study antipredation mechanisms of earthworms against ants. The experiments showed that earthworms do not escape predation by avoiding contact with ants in their nests. The earthworm mucus repelled the ants, suggesting a chemical defence against predation. Earthworms probably prevent the nest mounds from becoming overgrown by moulds and fungi, indicating possible mutualistic relationships between the earthworms and the ants. Received: 21 November 1996 / Accepted: 3 April 1997     

Behavior of red wood ants (Hymenoptera,Formicidae) during interaction with different symbiont partners

A comparative analysis of the behavior of Formica polyctena Först during interaction with different symbionts (free-living aphids Aphis grossulariae Kalt. and hidden larvae of the sawfly Blasticotoma filiceti Klug) was carried out. Red wood ants demonstrate different levels of functional differentiation in relatively constant groups of foragers collecting honeydew. A deep “professional” specialization with clear division of a number of tasks among foragers was studied in groups of ants tending aphids. Four professional groups of foragers with different tasks were revealed: “shepherds,” “guards,” “transporters,” and “scouts” (or “coordinators”). The groups of foragers caring for sawfly larvae mainly consist of unspecialized ants. Only few ants (about 5%) remain on duty on the fern plant near B. filiceti larvae and protect the food resource from competitors, especially from other ants. In addition, the ants demonstrate simpler behavior while collecting the larval excretion, resembling that at the sugar feeders. On the whole, the behavior of red wood ants is rather flexible. The level of functional differentiation in groups of foragers collecting honeydew is determined not only by the colony size and requirements but by the nature of their interaction with trophobionts, particularly, by the possibility of direct contact.     

Snapshot memories and landmark guidance in wood ants

Insects are thought to pinpoint a place by using memorized "snapshots," i.e., two-dimensional retinotopic views of the surrounding landmarks recorded when at the place (reviewed in ). Insects then reach the place by moving until their current view matches their snapshot. To determine when snapshots are recalled, and how differences between view and snapshot are translated into appropriate movements, we analyzed the approaches of wood ants to a feeding site that was located in the center of an array of two or three cylinders. In ants, contrary to flying hymenopterans, body orientation and direction of travel are collinear, so that an ant approaching an object always looks at it with frontal visual field. On their way to a food site, ants fixated and approached a cylinder predominantly when its angular size was smaller than when viewed from the food site. This finding implies that ants store snapshots at this place while fixating landmarks with frontal retina, so simplifying the later alignment of snapshots with their current view. It also means that ants recall snapshots well in advance of reaching the place. Although snapshots are centered on a landmark, we show that they extend at least 120 degrees into the periphery.     

Polydomy in ants: what we know, what we think we know, and what remains to be done

The correct identification of colony boundaries is an essential prerequisite for empirical studies of ant behaviour and evolution. Ant colonies function at various organizational levels, and these boundaries may be difficult to assess. Moreover, new complexity can be generated through the presence of spatially discrete subgroups within a more or less genetically homogeneous colony, a situation called polydomy. A colony is polydomous only if individuals (workers and brood) of its constituent nests function as a social and cooperative unit and are regularly interchanged among nests. This condition was previously called polycalic, and the term polydomy was used in a broader sense for a group of daughter nests of the same mother colony (implying limited female dispersal), without regard to whether these different nests continued to exchange individuals. We think that this distinction between ‘polycaly’ and ‘polydomy’ concerns two disparate concepts. We thus prefer the narrower definition of polydomy, which groups individuals that interact socially. Does this new level of organization affect the way in which natural selection acts on social traits? Here, after examining the history of terms, we review all ant species that have been described as expressing polydomous structures. We show that there is no particular syndrome of traits predictably associated with polydomy. We detail the existing theoretical predictions and empirical results on the ecology of polydomy, and the impact of polydomy on social evolution and investment strategies, while carefully distinguishing monogynous from polygynous species. Finally, we propose a methodology for future studies and offer ideas about what remains to be done. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 319–348.     

Response of the foraging behaviour of red wood ants (Formica rufa group) to exclusion from trees

Abstract 1 Because of the large numbers within a colony and their aggressive nature, red wood ants (Formica rufa group) have a potential to greatly influence the cold‐temperate forest ecosystem. Wood ants are omnivorous and hunt in trees as well as on the forest floor. 2 A field experiment in a mixed forest in central Sweden was carried out to examine (i) the foraging behaviour of wood ants on the forest floor and (ii) the impact of increased numbers of wood ants on the soil fauna. The foraging behaviour of wood ants was manipulated by excluding the ants from their food resources in the tree canopy, with the intention to increase ant activity on the forest floor. To estimate this activity, the number of trees with foraging ants, the numbers of ants going to and from their nests and the prey carried by home‐running wood ants were determined during the summer period. Pitfall traps were placed in the soil to determine effects on mobile soil invertebrates. 3 When excluded from local trees, wood ants searched other trees further away from the nests rather than searching more intensively for prey on the forest floor. By contrast to the initial hypothesis, more soil‐living prey were caught by ants in the control plots than in the plots where the local trees were not accessible to the wood ants. The proportion of soil‐living to tree‐living prey tended to be greater in the control plots. 4 In the treated plots (no access to the trees), wood ants had a negative effect on the activity of Linyphiidae spiders. There was little effect of wood ants on other soil invertebrates. 5 This study suggests that the role of wood ants as top predators in the forest soil food‐web in central Sweden is limited.     

Behavioral mechanisms of spatial competition between red wood ants (Formica aquilonia) and ground beetles (Carabidae)

Behavioral aspects of spatial competition between red wood ants (Formica aquilonia) and six mass species of Carabidae were studied in field and laboratory experiments. We showed that red wood ants essentially influence spatial distribution of ground beetles on their common territories. Transplantation experiments suggest that in newly established ants' settlements stronger forms of interrelations arise than in old stable colony. To examine the ability of beetles to avoid collisions with ants we used two experimental techniques. In laboratory, we tested carabids ability to avoid a clash in a Y-shaped labyrinth containing an active tethered ant in one section. In field experiments we compared quantitative characteristics of movements (such as crookedness of individual trajectories, speed of movement, the time spent on stops) for beetles placed close to ants foraging routes and on ant-free plots. All beetles studied displayed a clear tendency to learn, that is, to modity their behavior in order to avoid collisions with ants. Species that exhibited best parameters of learning were closer to ants by their size and characteristic movement, namely, Pterostichus oblogopunctatus and P. magus. Beetles' stereotyped behavioral tactics can be considered universal for avoiding collisions with any subject (for instance, with an ant) of a certain size and speed of movements. A set of tactics in the labyrinth included: (1) attempts to round the ant; (2) turns away after touching the ant with antennae; (3) turns away without a contact; (4) avoidances of a dangerous section; (5) stops near the ant with the antennae hidden. Comparing pairwise difference between four species shows that beetles use species-specific preference for definite combinations of tactics. Effective learning allows carabids to penetrate into ant foraging territory and partly avoide interference competition. It seems that red wood ants are not inclined to learn to avoid collisions with competing carabid species. Instead, they recognize an "enemy's image" and selectively attack relatively small predatory carabids rather than herbivorous species. Experiments with dummy beetles suggest that ants react for several hierarchically organized key characteristics of competitors such as speed of movement, dark color, bilateral symmetry, protuberances (legs, antennae), and smell. Among "professional" groups in ant family, guards and hunters react to beetles aggressively, whereas aphid tenders ignore them. Sophisticated combination of flexible and innate behavioral patterns enables insects to share territories and interact in the mode of relatively mild, spatial, competition instead of predation. Eliciting sets of hierarchically organized features of competitors that govern adjustment of spatial distribution in insects' community enable us to integrate ideas of classic and cognitive ethology.     

Characterization of microsatellite loci in red wood ants Formica (s. str.) spp. and the related genus Polyergus

Ants are interesting subjects for studies of evolution of altruism. We developed 13 microsatellite loci in a red wood ant Formica (s. str.) yessensis from random amplified polymorphic DNA fragments to study genetic structure within populations and colonies. Five loci bore two to five alleles in both F. (s. str.) yessensis and F. (s. str.) truncorum and two were also polymorphic in a related species, Polyergus samurai. Results suggest that the loci will be useful in evolutionary studies on Formica and Polyergus species.     

Within territory abundance of red wood ants Formica rufa is associated with the body condition of nestlings in the Eurasian treecreeper Certhia familiaris

Studies on individual reproductive success in relation to interspecific competition between distantly related taxa are scarce. We studied whether the abundance of red wood ants Formica rufa -group is related to the breeding habitat selection, fecundity and offspring quality in the Eurasian treecreeper Certhia familiaris, an old-growth forest passerine. The nest-box occupancy data were gathered over a five-year study period, whereas the breeding performance analyses were based on a two-year data set. The abundance of wood ants, measured within 50  m around the nest-boxes, was not related to nest-box occupancy rate, fecundity or the physiological stress of nestlings. In contrast, the abundance of wood ants was negatively related to the offspring quality and life-history traits, such as lowered body mass, subcutaneous fat reserves, and tarsus length at fledging. Our results suggest that exploitative competition between distantly related taxa may have considerable and adverse influences on nestling quality as measured by body mass, subcutaneous, fat and tarsus length. Red wood ants may decrease the fitness of treecreepers as the lower body condition of nestlings has the potential to impair recruitment into the breeding population and, additionally, impair the future reproductive effort.