Ant Formica Research Articles

Prey specialization and chemical mimicry between Formica archboldi and Odontomachus ants

Formica ants are not known to be prey specialists on other ant species, however, for the past 60 years, field observations on Formica archboldi in the southeastern United States have noted that their nests are scattered with body parts of Odontomachus trap-jaw ants. This study investigates the relationship between F. archboldi and Odontomachus. Through a series of behavioral experiments and a descriptive study of their chemical ecology, I find: (1) behavioral evidence that F. archboldi are more capable predators of Odontomachus in comparison to other Formica. (2) F. archboldi match the cuticular hydrocarbon profiles of the native species of Odontomachus that they occur with. This includes O. brunneus and O. relictus and the intraspecific variation found across Florida populations of O. brunneus. (3) F. archboldi do not display a prey retrieval preference towards hydrocarbon-matching Odontomachus as compared to mismatching. (4) F. archboldi that match Odontomachus hydrocarbon profiles do not receive lower levels of aggression than mismatching F. archboldi. Beyond providing natural history insights into the relationship between these species, this study expands our knowledge of an important insect chemical phenotype. The intraspecific variability in F. archboldi cuticular hydrocarbon profiles is among the greatest reported for social insects and provides a unique case of how non-parasitic species can generate parasite-like chemical-mimic phenotypes.

Progressive sensitivity of trophic levels to warming underlies an elevational gradient in ant–aphid mutualism strength

Although species interactions are often proposed to be stronger at lower latitudes and elevations, few studies have evaluated the mechanisms driving such patterns. In this study, we assessed whether, and by which mechanisms, abiotic changes associated with elevation altered the outcome of an ant–aphid protection mutualism. To do so, we characterized the multi‐trophic interactions among the ant Formica podzolica, the aphid Aphis varians, and aphid natural enemies occurring on the plant Chamerion angustifolium within replicate high and low elevation valleys. Low (versus high) elevation sites had longer summers (snowmelt 13 days earlier) and were on average 1.1°C warmer and 41% drier throughout the year. At low elevations, individual ant colonies consumed approximately double the volume of carbohydrate baits, likely due to a higher foraging tempo, and possibly due to a greater demand for sugar‐ versus protein‐rich resources (as indicated by stable isotope analysis). Wild aphid colonies at low elevations were visited by 1.4‐fold more natural enemies (controlling for variation in aphid abundance), while experimental aphid colonies on potted plants were tended 52% more frequently by ants. As a result, ants increased aphid colony survival by 66% at low elevations but had no detectable effect at high elevations; at low (versus high) elevations aphid colonies without ants had lower survival, demonstrating stronger predator effects, while aphid colonies with ants had higher survival, demonstrating even stronger ant benefits. Analyses for the effects of mean summer temperature yielded qualitatively identical results to those based on elevation. Collectively, these findings support predictions for a greater sensitivity of higher trophic levels to warming and demonstrate how species interactions can vary across environmental gradients due to simultaneous changes in species traits and abundances across multiple trophic levels.

The Preference of Some Myrmecochorous Plants of Forest Stands by Red Wood Ant (Formica rufa L.)—Experiment on Seeds with Elaiosomes

The paper is aimed in ants’ preference among seeds with elaiosomes. Seeds with elaiosomes of plants Asarum europaeum, Viola arvensis, Symphytum officinale, Chelidonium majus, and Ficaria verna were offered to red wood ants (Formica rufa) near two observed anthills. Monitored characteristics were the number of seeds collected by ants depending on the plant species, the presence of elaiosome, the orientation and the distance from anthill. The obtained data were processed by factorial ANOVA including PCA analysis. Seeds without elaiosomes were less preferred than the seeds with elaiosomes at statistical level. This experiment confirmed that elaiosomes attached to the seeds had significantly influenced transport of seeds by red wood ants. On the contrary, the influence of orientations (north–south) between seeds and the anthill were not proved. A distance of seeds from the anthill may play a certain role, but the results were not significant. Data indicated that ants had preferred seeds with elaiosomes of two plant species (A. europaeum and V. arvensis) from five species offered. The authors recommend to store seeds in a freezer before a similar experiment, because the elaisomes from different plant species will be fresh.

Trends in bacterial and fungal communities in ant nests observed with Terminal-Restriction Fragment Length Polymorphism (T-RFLP) and Next Generation Sequencing (NGS) techniques-validity and compatibility in ecological studies.

Microbes are ubiquitous and often occur in functionally and taxonomically complex communities. Unveiling these community dynamics is one of the main challenges of microbial research. Combining a robust, cost effective and widely used method such as Terminal Restriction Fragment Length Polymorphism (T-RFLP) with a Next Generation Sequencing (NGS) method (Illumina MiSeq), offers a solid alternative for comprehensive assessment of microbial communities. Here, these two methods were combined in a study of complex bacterial and fungal communities in the nest mounds of the ant Formica exsecta, with the aim to assess the degree to which these methods can be used to complement each other. The results show that these methodologies capture similar spatiotemporal variations, as well as corresponding functional and taxonomical detail, of the microbial communities in a challenging medium consisting of soil, decomposing plant litter and an insect inhabitant. Both methods are suitable for the analysis of complex environmental microbial communities, but when combined, they complement each other well and can provide even more robust results. T-RFLP can be trusted to show similar general community patterns as Illumina MiSeq and remains a good option if resources for NGS methods are lacking.

Individual behavioural type and group performance in Formica fusca ants

The link between individual and group-level behaviour may help understanding cooperation and division of labour in social animals. Despite the recent surge of studies, especially in social insects, the way individual differences translate into group performance remains debated. One hypothesis is that groups may simply differ in the average personality of their members and this would translate into inter-group differences in collective behaviour. We tested the hypothesis of a linear relationship between individual and group phenotype in the ant Formica fusca by using same-age groups of workers after measuring an individual behavioural trait. Individual exploratory activity in an open-field arena was significantly repeatable. Based on this trait, groups were composed, each consisting of 6 individuals with similar exploration tendency housed with 3 cocoons and a refuge. Individual exploratory activity was associated with the performance in cocoon recovery at the group level: groups composed of high exploratory individuals started transporting displaced cocoons significantly earlier and transported more cocoons into the refuge than groups with low exploratory workers. When in a group, more exploratory animals showed significantly more returns to the refuge than less exploratory ones and tended to transport more cocoons. These results show a direct linear link between individual and collective behaviour, suggesting that colony personality reflects the average personality of workers involved in a given task.

Weak population structure in the ant Formica fusca.

Dispersal is a fundamental trait of a species’ biology. High dispersal results in weakly structured or even panmictic populations over large areas, whereas weak dispersal enables population differentiation and strong spatial structuring. We report on the genetic population structure in the polygyne ant Formica fusca and the relative contribution of the dispersing males and females to this. We sampled 12 localities across a ∼35 km2 study area in Finland and generated mitochondrial DNA (mtDNA) haplotype data and microsatellite data. First, we assessed queen dispersal by estimating population differentiation from mtDNA haplotype data. Second, we analysed nuclear DNA microsatellite data to determine overall population genetic substructure in the study area with principal components analysis, Bayesian clustering, hierarchical F statistics and testing for evidence of isolation-by-distance. Third, we directly compared genetic differentiation estimates from maternally inherited mtDNA and bi-parentally inherited DNA microsatellites to test for sex-bias in dispersal. Our results showed no significant spatial structure or isolation by distance in neither mtDNA nor DNA microsatellite data, suggesting high dispersal of both sexes across the study area. However, mitochondrial differentiation was weaker (Fst-mt = 0.0047) than nuclear differentiation (Fst-nuc = 0.027), which translates into a sixfold larger female migration rate compared to that of males. We conclude that the weak population substructure reflects high dispersal in both sexes, and it is consistent with F. fusca as a pioneer species exploiting unstable habitats in successional boreal forests.

Caste-dependent brood retrieval by workers in the ant Formica exsecta

The ability to distinguish friends from foe is a widespread phenomenon among social animals. In ants, recognition of intruders is important for the maintenance of colony integrity and survival. Intruders are typically adult, but the acceptance of non-nestmate brood could result in severe fitness costs, depending on the caste of the brood. Accepting non-nestmate worker brood may not carry a cost, as they should not drain resources of the adoptive colony but may instead add to the workforce. Sexual brood, however, would typically not contribute to colony performance, yet require resources, and should thus be rejected. Here, we tested whether workers of the narrow-headed ant, Formica exsecta, which strongly discriminate between adult nestmates and non-nestmates, also discriminate between nestmate and non-nestmate pupae. Furthermore, we investigated whether the caste of the brood (workers/sexuals) affects discrimination. We carried out analysis of surface chemicals to investigate whether the chemical distance between colonies was associated with the propensity to accept non-nestmate pupae. We show that worker pupae were retrieved irrespective of their origin, whereas nestmate sexual pupae were retrieved at a slightly higher rate than non-nestmates. Our chemical data, however, suggest that both the reproductive and the worker brood carry sufficient chemical information for discrimination, as they both express colony signatures. However, this information is acted upon only in the case of sexual brood. Our results thus suggest that workers selectively capitalize on the chemical information in agreement with fitness predictions, albeit to a lower extent than during discrimination between adult individuals.

Effects of genetic relatedness, spatial distance, and context on intraspecifi c aggression in the red wood ant Formica pratensis (Hymenoptera: Formicidae)

In the present study, we tested the level of aggression of monodomous and polydomous colonies of the wood ant Formica pratensis (Hymenoptera: Formicidae) with a behavioral assay in nature and laboratory conditions to see if the ants from neighboring colonies are more tolerant or more aggressive to each other than those from greater distances. We also tested how context (nature and laboratory conditions) affected aggression. Our results showed that the monodomous colonies were highly aggressive to all neighboring or nonneighboring conspecifics in nature irrespective of the spatial distance. The polydomous colony showed no aggression towards neighboring conspecifics but the level of aggression increased with increasing spatial distance between the colonies. The level of aggression of tested colonies in laboratory conditions was significantly low, irrespective of whether they were monodomous or polydomous, indicating that aggression is context dependent. A DNA barcoding technique based on mitochondrial COI gene sequencing was applied to determine the genetic relatedness between the colonies. The results of the genetic analysis, in combination with results of behavioral assays, revealed that aggression behavior of the polydomous colony was affected by both the genetic relatedness and the spatial distance between the colonies while there was no clear separation of effects of genetic relatedness and spatial distance on aggression in the monodomous colonies.

TGFβ signaling related genes are involved in hormonal mediation during termite soldier differentiation.

A working knowledge of the proximate factors intrinsic to sterile caste differentiation is necessary to understand the evolution of eusocial insects. Genomic and transcriptomic analyses in social hymenopteran insects have resulted in the hypothesis that sterile castes are generated by the novel function of co-opted or recruited universal gene networks found in solitary ancestors. However, transcriptome analysis during caste differentiation has not been tested in termites, and evolutionary processes associated with acquiring the caste are still unknown. Termites possess the soldier caste, which is regarded as the first acquired permanently sterile caste in the taxon. In this study, we performed a comparative transcriptome analysis in termite heads during 3 molting processes, i.e., worker, presoldier and soldier molts, under natural conditions in an incipient colony of the damp-wood termite Zootermopsis nevadensis. Although similar expression patterns were observed during each molting process, more than 50 genes were shown to be highly expressed before the presoldier (intermediate stage of soldier) molt. We then performed RNA interference (RNAi) of the candidate 13 genes, including transcription factors and uncharacterized protein genes, during presoldier differentiation induced by juvenile hormone (JH) analog treatment. Presoldiers induced after RNAi of two genes related to TGFβ (Transforming growth factor beta) signaling were extremely unusual and possessed soldier-like phenotypes. These individuals also displayed aggressive behaviors similar to natural soldiers when confronted with Formica ants as hypothetical enemies. These presoldiers never molted into the next instar, presumably due to the decreased expression levels of the molting hormone (20-hydroxyecdysone; 20E) signaling genes. These results suggest that TGFβ signaling was acquired for the novel function of regulating between JH and 20E signaling during soldier differentiation in termites.

First record of the genus Thaumatopelvis Mahunka, 1973 (Acari: Prostigmata: Scutacaridae) from Asia with description of a new species associated with ants (Hymenoptera: Formicidae)

The mite species Thaumatopelvis lorasiacus Navabi & Hajiqanbar sp. nov. (Acari: Heterostigmata: Scutacaridae) associated with ants of the genera Formica Linnaeus, 1758 and Pheidole Westwood, 1839 (Hymenoptera: Formicidae) is described form Borujerd, Lorestan Province, western Iran. This finding presents the first evidence of the genus Thaumatopelvis Mahunka, 1973 from Asia and a new association between ants of the genera Formica and Pheidole with mites of this genus. A key to world species of the Thaumatopelvis is also provided.

Chemical Characterization of Young Virgin Queens and Mated Egg-Laying Queens in the Ant Cataglyphis cursor: Random Forest Classification Analysis for Multivariate Datasets.

Social insects are well known for their extremely rich chemical communication, yet their sex pheromones remain poorly studied. In the thermophilic and thelytokous ant, Cataglyphis cursor, we analyzed the cuticular hydrocarbon profiles and Dufour's gland contents of queens of different age and reproductive status (sexually immature gynes, sexually mature gynes, mated and egg-laying queens) and of workers. Random forest classification analyses showed that the four groups of individuals were well separated for both chemical sources, except mature gynes that clustered with queens for cuticular hydrocarbons and with immature gynes for Dufour's gland secretions. Analyses carried out with two groups of females only allowed identification of candidate chemicals for queen signal and for sexual attractant. In particular, gynes produced more undecane in the Dufour's gland. This chemical is both the sex pheromone and the alarm pheromone of the ant Formica lugubris. It may therefore act as sex pheromone in C. cursor, and/or be involved in the restoration of monogyny that occurs rapidly following colony fission. Indeed, new colonies often start with several gynes and all but one are rapidly culled by workers, and this process likely involves chemical signals between gynes and workers. These findings open novel opportunities for experimental studies of inclusive mate choice and queen choice in C. cursor.

Coal Industry Impact on Ants of the Genus Formica (Hymenoptera: Formicidae)

The peculiarities of the settlement of ants of the genus Formica have been studied at the areas affected by varying degreesof impact made by enterprises of surface (opencast mines) and underground (deep mines) coal hard mining. It has been revealed that Formica ants. str. are the most sensitive to any impact and in overwhelming cases disappear from the contaminated area. On the contrary, the representatives of Serviformica are more environmentally flexible, and are able to occupy areas with anaverage degree of contamination. However, the density of the settlement and the abundance remain low. After the cessation of coal mining near opencast mines, the recovery of myrmecofauna occurs more rapidly (7-10 years) than near deep mines (more than50 years). The higher the degree of contamination of the area, the lighter the colour of the ants. The proportion of insect larvae in the Formica rufa food sharply increases in the contaminated area.

Mass Occurrence and Dominant Behavior of the European Ant Species Formica fuscocinerea (Forel)

Recently, masses of the ant Formica (Serviformica) fuscocinerea (Forel) have been occurring at numerous sites in Southern Germany. Although F. fuscocinerea is native to Southern Germany, these mass occurrences resemble ant invasions in density and dominance. This study aimed to investigate the underlying mechanisms that promote sudden mass occurrence of a previously inconspicuous ant species within its native range. To estimate the competitive dominance of F. fuscocinerea, species occurrence and abundance considering biotic and abiotic parameters were studied in a natural habitat where F. fuscocinerea co-occurred with two other common ant species, Myrmica ruginodis (Nylander) and Lasius niger (Linnaeus). To understand the species’ distribution in the field, laboratory experiments on interspecific competition were conducted. Finally, the colony structure of F. fuscocinerea was investigated with intraspecific aggression tests. Formica fuscocinerea dominated an area that, as indicated by strongly frequented foraging trails on the trees, provided important food sources, e.g. trophobionts, to the ants. Other ant species coexisted only at the periphery of the F. fuscocinerea range. Laboratory experiments revealed F. fuscocinerea as highly dominant species. Additionally, F. fuscocinerea showed a complete lack of intraspecific aggression between ants originating from distances up to 58 km, indicating weak or nonexistent behavioral boundaries among ants of physically separated nests. Since extraordinarily high worker densities, strong interspecific dominance and a lack of colony boundaries within supercolonies are considered to be important traits of several invasive ant species we conclude that the same traits also promote the dominance of F. fuscocinerea.

Ant–aphid relations in the south of Western Siberia (Hymenoptera: Formicidae; Hemiptera: Aphididae)

Aphids, the main suppliers of energy-rich honeydew, play an important role in the life of ants. However, the data on the trophobiotic ant–aphid associations in the majority of regions are still limited. We present the first data on the ant–aphid relations in the south of Western Siberia. Investigations were carried out in the most typical biotopes of forest-steppe and steppe zones in the territory of Novosibirsk and Kurgan regions (Russia) during 1993–2014. There were revealed 35 species of ants and 198 species of aphids. Detected 456 ant–aphid associations involved 28 ant species and 134 myrmecophilous aphids. Seven ant species were found to consume honeydew of 9 non-myrmecophilous aphids, scraping it from the plant. This behaviour is typical of subdominant and subordinate ants which do not protect their foraging areas. Ants associate with various numbers of aphid species. About 36% of ants attended aphid colonies of less than 5 species. The largest number of myrmecophilous aphids is associated with L. niger (Linnaeus, 1758) (103 species), Formica pratensis Retzius, 1783 (50), Formica rufa group (25–33), F. (Serviformica) fusca Linnaeus, 1758 (26) and F. (S.) cunicularia Latreille, 1798 (27). Different ants play unequal roles in the formation of trophobiotic interactions with aphids. Due to complex territorial and foraging behaviour, including high functional specialization among honeydew collectors, dominant ants of Formica s. str. are one of the leaders in this process. The role of L. niger and Formica ants of the subgenus Serviformica requires further detailed investigation.

Distribution of oribatid mites is moisture-related within red wood ant Formica polyctena nest mounds

Abundant and species rich oribatid mite faunas live as ant associates in red wood ant nest mounds. Distribution of oribatids (as of many other groups) within mounds is unknown, yet there is an indication that many oribatid species favor moist microclimates. The ant mounds typically have a relatively dry core covered by a moister surface layer, but the moisture variance of mound parts has rarely been verified by measurements. We measured the moisture variance of nine Formica polyctena mounds (surface, rim, core) located in three different forest types in Finland. The moisture may affect the mounds’ temperature maintenance, and we further investigated this relationship. We also hypothesised that the abundance, species richness and community composition of oribatids may be related to the moisture, and investigated these differences between the mound parts and forest types. The moisture varied significantly between the mound parts; moisture was highest in surface followed by rim and core. The surface moisture had a positive relationship with nest core temperature. A total of 18,614 oribatid mites belonging to 93 species and one higher taxon were recorded. The oribatids occurred predominantly on the surface (77.9%), followed by the rim (16.6%) and the core (5.5%) of the ant nest mounds. The abundance and species richness of oribatids was positively related to moisture and differed significantly between the mound parts and forest types. The mound volume had no effect on moisture, temperature or mite community composition. The results indicate that the moisture harbored in the surface layer of ant nest mounds is a vital factor for maintaining rich oribatid mite communities within mounds.

Transcriptome sequencing reveals high isoform diversity in the ant Formica exsecta.

Transcriptome resources for social insects have the potential to provide new insight into polyphenism, i.e., how divergent phenotypes arise from the same genome. Here we present a transcriptome based on paired-end RNA sequencing data for the ant Formica exsecta (Formicidae, Hymenoptera). The RNA sequencing libraries were constructed from samples of several life stages of both sexes and female castes of queens and workers, in order to maximize representation of expressed genes. We first compare the performance of common assembly and scaffolding software (Trinity, Velvet-Oases, and SOAPdenovo-trans), in producing de novo assemblies. Second, we annotate the resulting expressed contigs to the currently published genomes of ants, and other insects, including the honeybee, to filter genes that have annotation evidence of being true genes. Our pipeline resulted in a final assembly of altogether 39,262 mRNA transcripts, with an average coverage of >300X, belonging to 17,496 unique genes with annotation in the related ant species. From these genes, 536 genes were unique to one caste or sex only, highlighting the importance of comprehensive sampling. Our final assembly also showed expression of several splice variants in 6,975 genes, and we show that accounting for splice variants affects the outcome of downstream analyses such as gene ontologies. Our transcriptome provides an outstanding resource for future genetic studies on F. exsecta and other ant species, and the presented transcriptome assembly can be adapted to any non-model species that has genomic resources available from a related taxon.

Increased Risk Proneness or Social Withdrawal? The Effects of Shortened Life Expectancy on the Expression of Rescue Behavior in Workers of the ant\xa0Formica cinerea (Hymenoptera: Formicidae)

In social insects behavioral consequences of shortened life expectancy include, among others, increased risk proneness and social withdrawal. We investigated the impact of experimental shortening of life expectancy of foragers of the ant Formica cinerea achieved by their exposure to carbon dioxide on the expression of rescue behavior, risky pro-social behavior, tested by means of two bioassays during which a single worker (rescuer) was confronted with a nestmate (victim) attacked by a predator (antlion larva capture bioassay) or immobilized by an artificial snare (entrapment bioassay). Efficacy of carbon dioxide poisoning in shortening life expectancy was confirmed by the analysis of ant mortality. Rescue behavior observed during behavioral tests involved digging around the victim, transport of the sand covering the victim, pulling the limbs/antennae/mandibles of the victim, direct attack on the antlion (in antlion larva capture tests), and snare biting (in entrapment tests). The rate of occurrence of rescue behavior was lower in ants with shortened life expectancy, but that effect was significant only in the case of the entrapment bioassay. Similarly, only in the case of the entrapment bioassay ants with shortened life expectancy displayed rescue behavior after a longer latency and devoted less time to that behavior than ants from the control groups. Our results demonstrated that in ant workers shortened life expectancy may lead to reduced propensity for rescue behavior, most probably as an element of the social withdrawal syndrome that had already been described in several studies on behavior of moribund ants and honeybees.

No evidence for tactile communication of direction in foraging Lasius ants

The idea that ants communicate when meeting on a trail is beguiling, but evidence for this is scarce. Physical communication in ants has been demonstrated to play a role as a modulator of behaviours such as alarm and recruitment. Honeybees can communicate the location of a resource using an advanced motor display—the waggle dance. However, no equivalent of the waggle dance has been described for any ant species, and it is widely believed that ants cannot communicate the location of resources using motor displays. One group of researchers report several demonstrations of such communication in Formica ants; however, these results have been largely ignored. More recently some evidence arose that Lasius niger foragers returning from a food source can communicate to outgoing foragers the direction that should be taken at the next bifurcation by means of physical contact on the trail. Here, we make a concerted effort to replicate these results. Although initial results seemed to indicate physical communication, once stringent controls to eliminate pheromone cues were put in place, no evidence for physical communication of food location could be found. This null result was replicated independently by a different research group on a closely related species, L. neglectus. We conclude that neither L. niger nor L. neglectus foragers communicate resource location using physical contact. Our results increase the burden of proof required for other claims of physical communication of direction in ants, but do not completely rule out this possibility.

Response of a Predatory ant to Volatiles Emitted by Aphid- and Caterpillar-Infested Cucumber and Potato Plants.

In response to herbivory by insects, various plants produce volatiles that attract enemies of the herbivores. Although ants are important components of natural and agro-ecosystems, the importance of herbivore-induced plant volatiles (HIPVs) as cues for ants for finding food sources have received little attention. We investigated responses of the ant Formica pratensis to volatiles emitted by uninfested and insect-infested cucumber (Cucumis sativus) and potato (Solanum tuberosum) plants. Cucumber plants were infested by the phloem-feeding aphid Aphis gossypii, the leaf chewer Mamestra brassicae or simultaneously by both insects. Potato plants were infested by either Aphis gossypii, by the leaf chewer Chrysodeixis chalcites or both. In olfactometer experiments, ants preferred volatile blends emitted by cucumber plants infested with M. brassicae caterpillars alone or combined with A. gossypii to volatiles of undamaged plants or plants damaged by A. gossypii only. No preference was recorded in choice tests between volatiles released by aphid-infested plants over undamaged plants. Volatiles emitted by potato plants infested by either C. chalcites or A. gossypii were preferred by ants over volatiles released by undamaged plants. Ants did not discriminate between potato plants infested with aphids and caterpillars over plants infested with aphids only. Plant headspace composition showed qualitative and/or quantitative differences between herbivore treatments. Multivariate analysis revealed clear separation between uninfested and infested plants and among herbivore treatments. The importance of HIPVs in indirect plant defence by ants is discussed in the context of the ecology of ant-plant interactions and possible roles of ants in pest management.

Not simply red: Colouration of red wood ant Formica rufa (Hymenoptera: Formicidae) is polymorphic, modular and size-dependent

Insects produce pigment and structural colours mainly for camouflage, signaling, physical protection or temperature regulation, and colour patterns can provide information about individual quality. Although the evolutionary function and nature of the variability in colouration are well known for many invertebrate taxa, there is little information on this topic for ants. We studied individual variation in the melanin-based colour traits of workers of the red wood ant, Formica rufa (Hymenoptera: Formicidae), from 20 colonies in Southern Finland and revealed the type of colouration in this species. First, using the threshold approach we distinguished between continuous and discrete variations. Furthermore, the analyses affirmed nine discrete morphs in terms of the colouration on the head and eight on the pronotum, while only continuous variation were found on the other body parts. Measuring the size of a particular colour pattern, the intensity of colour expression (degree of melanization) and statistical analyses allowed an assessment of the intra-individual variation in both discrete and continuous patterns. The results revealed substantial modularity in the above mentioned colouration traits. In workers of F. rufa there were individuals with a dark head and light coloured thorax and vice a versa. Size of the dark pigment colour patterns exhibited less modularity than the degree of melanization. Finally, the interrelation between colouration traits and individual body size revealed their size-dependent origin. Small individuals had relatively larger areas of colour on the head and thorax than big individuals. These results are likely to facilitate further taxonomical and ecological studies on red wood ants, as they show it is possible to assess colouration traits in ants. However, more studies are needed on the function of polymorphism and modular colouration in this group of ants.