Species‐level predation network uncovers high prey specificity in a Neotropical army ant community

Army ants are among the top arthropod predators and considered keystone species in tropical ecosystems. During daily mass raids with many thousand workers, army ants hunt live prey, likely exerting strong top‐down control on prey species. Many tropical sites exhibit a high army ant species diversity (>20 species), suggesting that sympatric species partition the available prey niches. However, whether and to what extent this is achieved has not been intensively studied yet. We therefore conducted a large‐scale diet survey of a community of surface‐raiding army ants at La Selva Biological Station in Costa Rica. We systematically collected 3,262 prey items from eleven army ant species (genera Eciton, Nomamyrmex and Neivamyrmex). Prey items were classified as ant prey or non‐ant prey. The prey nearly exclusively consisted of other ants (98%), and most booty was ant brood (87%). Using morphological characters and DNA barcoding, we identified a total of 1,103 ant prey specimens to the species level. One hundred twenty‐nine ant species were detected among the army ant prey, representing about 30% of the known local ant diversity. Using weighted bipartite network analyses, we show that prey specialization in army ants is unexpectedly high and prey niche overlap very small. Besides food niche differentiation, we uncovered a spatiotemporal niche differentiation in army ant raid activity. We discuss competition‐driven multidimensional niche differentiation and predator–prey arms races as possible mechanisms underlying prey specialization in army ants. By combining systematic prey sampling with species‐level prey identification and network analyses, our integrative approach can guide future research by portraying how predator–prey interactions in complex communities can be reliably studied, even in cases where morphological prey identification is infeasible.     

Spatial Variation in Army Ant Swarm Raiding and its Potential Effect on Biodiversity

Invertebrate communities of the tropical rain forest floor are highly diverse, characterized by patchy species distribution patterns and high variation in species density. Spatial variation in the foraging activity of swarm raiding army ants, prime invertebrate predators in tropical rain forests, is discussed as a mechanism contributing to these patterns, but highly resolved long‐term data on army ant raiding on the local and landscape scale are hitherto lacking. In this study, 196 positions in 11 study sites in a tropical rain forest in western Kenya were continuously monitored over ~4 mo for the occurrence of swarm raids of army ants. Using population simulation analyses, the consequences of army ant raiding for prey communities were assessed. We found an unexpectedly high variation in raid rates at the study site and landscape scale. The weekly chance of communities to become raided by army ants was on average 0.11, but ranged from 0 to 0.50 among the 196 positions. Simulating population developments of two Lotka–Volterra species—showing slight trade‐offs between competitive strength and resistance to army ant raids—in the real raiding landscapes showed that the observed spatial variation in raid rates may produce high prey diversity at larger spatial scales (due to high β‐diversity) and strong variation in species density. Our results indicate that high spatial variation in army ant swarm raiding is a mechanism capable of generating patchy species distribution patterns and maintaining the high biodiversity of invertebrate communities of the tropical rain forest floor.     

How much do army ants eat? On the prey intake of a neotropical top-predator

New World army ants (Ecitoninae) are nomadic group-predators that are widely thought to have a substantial impact on their prey. Nevertheless, quantitative data on prey intake by army ants is scarce and mostly limited to chance encounters. Here, I quantify the prey intake of the army ant Eciton hamatum at the contrasting scales of raid, colony (sum of simultaneous raids), and population. Like most army ants, E. hamatum conducts narrow ‘column raids’ and has a specialized diet of ant prey. I show that individual raids often had periods of no prey intake, and raid intake rates, calculated in g/min, differed significantly among colonies. Moreover, neither mean nor peak raid intake rates were correlated with colony size. Similarly, colony intake rates differed significantly among colonies, and mean colony intake rates were not correlated with colony size. However, mean colony intake rates were significantly higher than mean raid intake rates, and peak colony intake rate was correlated with colony size. Having multiple raids thus improves colony-level intake rates, and larger colonies can harvest more prey per unit time. Mean colony intake rate across colonies was 0.067 g/min dry weight and mean daily colony intake was calculated at 38.2 g. This intake is comparable to that of Eciton burchellii, which has a more generalized diet and conducts spectacular ‘swarm raids’ that are seen as having a greater impact on prey than column raids. Population size on Barro Colorado Island, Panama, was estimated to be 57 colonies, which extrapolates to a daily population intake of nearly 2 kg of prey dry weight, or 120 g/km². Broadly, these findings demonstrate that column raiding army ants experience considerable variation in prey intake for individual raids, but can still achieve notable impact at the larger scales of colony and population. Furthermore, they challenge the idea that swarm-raiding species necessarily have greater intake and thus impact on prey. Instead, I suggest that conducting multiple column raids may be a strategy that allows for comparable intake from a more specialized diet.     

Morphological phylogeny of army ants and other dorylomorphs (Hymenoptera: Formicidae)

Abstract. The dorylomorph group of ants comprises the three subfamilies of army ants (Aenictinae, Dorylinae, Ecitoninae) together with the subfamilies Aenictogitoninae, Cerapachyinae, and Leptanilloidinae. We describe new morphological characters and synthesize data from the literature in order to present the first hypothesis of phylogenetic relationships among all dorylomorph genera. These data include the first available character information from the newly discovered male caste of Leptanilloidinae. We used ant taxa from Leptanillinae, Myrmeciinae, and the poneromorph (Ponerinae sensu lato) subfamilies Amblyoponinae, Ectatomminae, and Paraponerinae as outgroups. We scored a total of 126 characters from twenty-two terminal taxa and used these data to conduct maximum parsimony and bootstrap analyses. The single most-parsimonious tree and bootstrap results support a single origin of army ants. The Old World army ant genus Dorylus forms a monophyletic group with the enigmatic genus Aenictogiton, which is currently known only from males; the second Old World army ant genus Aenictus is sister to this clade. This result generates the prediction that females of Aenictogiton, when discovered, will be observed to possess the army ant syndrome of behavioural and reproductive traits. The monophyly of the New World army ants (Ecitoninae) is supported very strongly, and within this group the genera Eciton, Nomamyrmex, and Labidus form a robust clade. The monophyly of Leptanilloidinae is also upheld. The subfamily Cerapachyinae appears paraphyletic, although this conclusion is not supported by strong bootstrap results. Relationships among genera of Cerapachyinae similarly are not resolved robustly, although parsimony results suggest clades consisting of (Acanthostichus + Cylindromyrmex) and (Cerapachys + Sphinctomyrmex). We tested for the effect of incompletely known taxa by conducting a secondary analysis in which the two genera containing ∼50% missing character data (Aenictogiton and Asphinctanilloides) were removed. The strict consensus of the seventeen most-parsimonious trees from this secondary analysis is poorly resolved outside the army ants and contains no clades conflicting with the primary analysis. The position of Leptanilla shifts from forming the sister group to Leptanilloidinae (without high bootstrap support) in the primary analysis, to falling within a polytomy at the base of the root of the dorylomorphs when incompletely known taxa are removed. This instability suggests that the placement of Leptanilla within the dorylomorphs in our primary analysis may be spurious.     

A new genus of hell ants from the Cretaceous (Hymenoptera: Formicidae: Haidomyrmecini) with a novel head structure

An unusual Cretaceous trap jaw ant is described from Burmese amber dated to the Late Cretaceous. Linguamyrmex vladi gen.n. sp.n. is distinguished by an unusual suite of morphological characters indicating specialized predatory behaviour and an adaptive strategy no longer found among modern ant lineages. The clypeus, highly modified as in other closely related haidomyrmecine hell ants, is equipped with a paddle‐like projection similar to Ceratomyrmex. X‐ray imaging reveals that this clypeal paddle is reinforced, most probably with sequestered metals. Presumably this fortified clypeal structure was utilized in tandem with scythe‐like mandibles to pin and potentially puncture soft‐bodied prey. This unique taxon, which stresses the diversity of stem‐group ants, is discussed in the context of modern and other Cretaceous trap jaw ant species. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:40D636A3‐4D88‐470A‐BC5B‐85ABFD1A49E2 .     

Foraging behavior of Cerulean Warblers during the breeding and non‐breeding seasons: evidence for the breeding currency hypothesis

Birds require additional resources for raising young, and the breeding currency hypothesis predicts that insectivorous species exploit large soft‐bodied prey during the breeding season, but shift to small, likely hard‐bodied, prey during the non‐breeding season. To test this hypothesis, we examined prey use by Cerulean Warblers (Setophaga cerulea), foliage‐gleaning Nearctic‐Neotropical migrants, during the breeding and non‐breeding seasons. We collected data on foraging behavior during the breeding season (including observations of prey items fed to young) in upland mixed‐oak forest in southeastern Ohio in 2009 and 2010 and, during the non‐breeding season, in shade coffee in the Cordillera de Merida, Venezuela, in 2008–2009. Cerulean Warblers captured 7% more large prey (visible prey extending beyond the bill) during the breeding than the non‐breeding season, but foraged at similar rates during both seasons. Large, soft‐bodied prey appeared to be especially important for feeding young. We found that adults delivered large prey on >50% of provisioning visits to nests and 69% of identifiable large prey fed to nestlings were greenish larvae (likely Lepidoptera or caterpillars) that camouflage against leaves where they would tend to be captured by foliage‐gleaning birds. Availability of specific taxa appeared to influence tree species foraging preferences. As reported by other researchers, we found that Cerulean Warblers selected trees in the genus Carya for foraging and our examination of caterpillar counts from the central Appalachian Mountains (Butler and Strazanac 2000 ) showed that caterpillars with greenish coloration, especially Baileya larvae, may be almost twice as abundant on Carya than Quercus. Our results provide evidence for the breeding currency hypothesis, and highlight the importance of caterpillars to a foliage‐gleaning migrant warbler of conservation concern.     

Chimpanzees prey on army ants with specialized tool set

Several populations of chimpanzees have been reported to prey upon Dorylus army ants. The most common tool‐using technique to gather these ants is with “dipping” probes, which vary in length with regard to aggressiveness and lifestyle of the prey species. We report the use of a tool set in army ant predation by chimpanzees in the Goualougo Triangle, Republic of Congo. We recovered 1,060 tools used in this context and collected 25 video recordings of chimpanzee tool‐using behavior at ant nests. Two different types of tools were distinguished based on their form and function. The chimpanzees use a woody sapling to perforate the ant nest, and then a herb stem as a dipping tool to harvest the ants. All of the species of ants preyed upon in Goualougo are present and consumed by chimpanzees at other sites, but there are no other reports of such a regular or widespread use of more than one type of tool to prey upon Dorylus ants. Furthermore, this tool set differs from other types of tool combinations used by chimpanzees at this site for preying upon termites or gathering honey. Therefore, we conclude that these chimpanzees have developed a specialized method for preying upon army ants, which involves the use of an additional tool for opening nests. Further research is needed to determine which specific ecological and social factors may have shaped the emergence and maintenance of this technology. Am. J. Primatol. 72:17–24, 2010. © 2009 Wiley‐Liss, Inc.     

Consumption of introduced prey by native predators: Argentine ants and pit-building ant lions

When populations of native predators are subsidized by numerically dominant introduced species, the structure of food webs can be greatly altered. Surprisingly little is known, however, about the general factors that influence whether or not native predators consume introduced species. To learn more about this issue, we examined how native pit-building ant lions (Myrmeleon) are affected by Argentine ant (Linepithema humile) invasions in coastal southern California. Compared to areas without L. humile, invaded areas contained few native ant species and were deficient in medium-sized and large bodied native ants. Based on these differences, we predicted that Argentine ants would negatively affect ant lion larvae. Contrary to this expectation, observational surveys and laboratory growth rate experiments revealed that Myrmeleon were heavier, had longer mandibles, and grew more quickly when their main ant prey were Argentine ants rather than native ants. Moreover, a field transplant experiment indicated that growth rates and pupal weights were not statistically different for larval ant lions reared in invaded areas compared to those reared in uninvaded areas. Argentine ants were also highly susceptible to capture by larval Myrmeleon. The species-level traits that presumably make Argentine ant workers susceptible to capture by larval ant lions—small size and high activity levels—appear to be the same characteristics that make them unsuitable prey for vertebrate predators, such as horned lizards. These results underscore the difficulties in predicting whether or not numerically dominant introduced species serve as prey for native predators.     

Coordination of Raiding and Emigration in the Ponerine Army Ant Leptogenys distinguenda (Hymenoptera: Formicidae: Ponerinae): A Signal Analysis

Several glandular sources of trail pheromones have been discovered in army ants in general. Nevertheless, at present the understanding of the highly coordinated behavior of these ants is far from complete. The importance of trail pheromone communication for the coordination of raids and emigrations in the ponerine army ant Leptogenys distinguenda was examined, and its ecological function is discussed. The secretions of at least two glands organize the swarming activities of L. distinguenda. The pygidial gland is the source of an orientation pheromone holding the group of raiding workers together. The same pheromone guides emigrations to new nest sites. In addition, the poison sac contains two further components: one with a weak orientation effect and another which produces strong, but short-term attraction and excitement. The latter component is important in prey recruitment and characterizes raid trails. This highly volatile recruitment pheromone allows the extreme swarm dynamic characteristic of this species. Emigration trails lack the poison gland secretion. Due to their different chemical compositions, the ants are thus able to distinguish between raid and emigration trails. Nest emigration is not induced chemically, but mechanically, by the jerking movements of stimulating workers.     

Foraging dynamics in the group-hunting myrmicine ant,Pheidologeton diversus

Pheidologeton diversus workers group-hunt (that is, search for food in raiding groups) and are in this way remarkably convergent with army ants (Dorylinae and Ecitoninae). Raids appear usually to take independent courses and are capable of tracking areas of high food density. However, raid advance is not dependent on continual food discovery at the raid front, since raids can advance over areas without food. Most raids extend from trunk trails, which originate when the basal trail of a raid remains in use even after the original raid has ceased. Trunk trails can last at least as long as 10 weeks, with the terrain and the distance to the nest influencing the trail stability. Territories are limited to the trail systems, with rich food items in particular being vigorously defended. Group hunting permits P. diversus to quickly harvest booty, usurp foods from competing species, and capture large prey. This strategy is compared with the raiding strategies of other ants. I hypothesize that group hunting originated from an ancestor which hunted solitarily from trunk trails through the acceleration of trail production and reduction in worker autonomy.     

Strict monandry in the ponerine army ant genus Simopelta suggests that colony size and complexity drive mating system evolution in social insects

Altruism in social insects has evolved between closely related full-siblings. It is therefore of considerable interest why some groups have secondarily evolved low within-colony relatedness, which in turn affects the relatedness incentives of within-colony cooperation and conflict. The highest queen mating frequencies, and therefore among the lowest degrees of colony relatedness, occur in Apis honeybees and army ants of the subfamilies Aenictinae, Ecitoninae, and Dorylinae, suggesting that common life history features such as reproduction by colony fission and male biased numerical sex-ratios have convergently shaped these mating systems. Here we show that ponerine army ants of the genus Simopelta, which are distantly related but similar in general biology to other army ants, have strictly monandrous queens. Preliminary data suggest that workers reproduce in queenright colonies, which is in sharp contrast to other army ants. We hypothesize that differences in mature colony size and social complexity may explain these striking discrepancies.     

The blind leading the blind in army ant raid patterns: Testing a model of self-organization (Hymenoptera: Formicidae)

We present field experiments and analyses that test both the assumptions and the predictions of a model that showed how the swarm raids of the army ant Eciton burchellimight be self-organizing, i.e., based on hundreds of thousands of interactions among the foraging workers rather than a central administration or hierarchical control. We use circular mill experiments to show that the running velocity of the ants is a sigmoidal function of the strength of their trail pheromones and provide evidence that the swarm raid is structured by the interaction between outbound and inbound forager traffic mediated by the pheromones produced by both of these sets of ants. Inbound traffic is also affected by the distribution of prey, and hence, sites of prey capture alter the geometry of the raid. By manipulating the prey distributions for E. burchelliswarms, we have made them raid in a form more typical of other army ant species. Such self-organization of raids based on an interaction between the ants and their environment has profound consequences for interpretations of the evolution of army ant species.     

Geographical variation in mandible morphologies specialised for collembolan predation depend on prey size in the ant Strumigenys lewisi

1. Ants in the genus Strumigenys are predator ants that feed on tiny soil arthropods. The mandibles are modified into high‐speed traps to capture swift collembolan prey. The peculiar mandible morphologies of these ants have evolved depending on characteristics of the prey. Specifically, the evolution of mandible size and shape may be directly driven by prey size. 2. In the present study, the intraspecific variation of the morphological traits of Strumigenys lewisi populations were observed in central Japan. The relationships between the morphological variations and the prey body size were analysed. 3. In workers and queens, three morphological traits, head width, mandible length, and mandible width were significantly different among the multiple sites. Specifically, the mandible length was shorter in southwestern Japan than in other sampling locations. The ancova model revealed that the allometry of the mandible length to the head width was different among the sites. 4. As predicted, the mandible length was positively correlated with the average body size of collembolans in the Entomobryidae family. Furthermore, multiple regression analysis showed that the variation of the mandible length was affected by environmental factors represented as location information. However, the effect of collembolan body size was more effective at predicting mandible length. The study suggests that the geographical variation of mandible morphologies in S. lewisi has been selected by predator–prey interactions with collembolans.     

Combat between large derived societies: A subterranean army ant established as a predator of mature leaf-cutting ant colonies

Summary. Mature colonies of Atta leaf-cutting ants are dominant herbivores throughout the Neotropics. Although young colonies have natural enemies, mature colonies, which live in extensive nests containing millions of workers, currently have no recognised predators. New World army ants (Ecitoninae) are specialist social predators of other ants, and the army ant Nomamyrmex esenbeckii, a primarily subterranean species, is known to prey upon young Atta colonies. Here we present the results of the first long-term study of the predator-prey interaction between N. esenbeckii and Atta. Our study establishes the army ant N. esenbeckii as the only known predator capable of successfully attacking and killing mature as well as young colonies of Atta leaf-cutting ants. In natural raids, and experimental tests, Atta rapidly recruited their largest workers (majors) as a specific defensive response to N. esenbeckii raiders and both taxa used their largest individuals in the frontline of battles. The deployment and behaviour of these large workers demonstrates a size-related division of labour and agrees with the predictions of Lanchesters Linear Law of Combat. Both taxa also used cooperative combat teams to overwhelm large combatants from the other side. The success of N. esenbeckii raids varied greatly, such that they were prevented from entering Atta nests in the least successful raids, and completely overran Atta colonies in the most successful raids. The speed and magnitude of the defensive response of mature Atta colonies was key in determining the level of success of N. esenbeckii raids.Received 12 December 2003; revised 25 March 2004; accepted 1 April 2004.Work conducted at the Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Ancon, Republic of Panama     

Birds and army ants in a fragment of the Atlantic Forest of Brazil

ABSTRACT Little is known about the birds associated with army‐ant swarms in the Brazilian Atlantic forest. Our objectives were to locate and monitor army‐ant swarms in the Atlantic rainforest of Brazil and to identify the species of birds that attended the swarms and exhibited bivouac‐checking behavior. From July 2004 to August 2005, we located 49 swarms of army ants, including 28 Eciton burchelli, 19 Labidus praedator, and 2 Eciton vagans swarms. No birds were present at 17 (35%) swarms. At 32 swarms where birds were present, 22 (69%) were E. burchelli swarms and 10 (31%) were L. praedator swarms. No birds were observed at the two E. vagans swarms. We identified 66 species of birds attending the swarms, but only 43 species were observed foraging on prey flushed by the ants. Eighteen of these species had not been previously reported to forage in association with army‐ant swarms. Most birds observed during our study attended army‐ant swarms opportunistically, with White‐shouldered Fire‐eyes (Pyriglena leucoptera) the only obligate ant follower. Our observations suggest that the arthropods and other organisms flushed by army ants represent an important food resource for several species of birds in the Atlantic forest ecosystem.     

Species-Specific Effects of Ant Inhabitants on Bromeliad Nutrition

Predator activities may lead to the accumulation of nutrients in specific areas of terrestrial habitats where they dispose of prey carcasses. In their feeding sites, predators may increase nutrient availability in the soil and favor plant nutrition and growth. However, the translocation of nutrients from one habitat to another may depend on predator identity and diet, as well as on the amount of prey intake. Here we used isotopic (¹⁵N) and physiological methods in greenhouse experiments to evaluate the effects of the identity of predatory ants (i.e., the consumption of prey and nest sites) on the nutrition and growth of the bromeliad Quesnelia arvensis. We showed that predatory ants with protein-based nutrition (i.e., Odontomachus hastatus, Gnamptogenys moelleri) improved the performance of their host bromeliads (i.e., increased foliar N, production of soluble proteins and growth). On the other hand, the contribution of Camponotus crassus for the nutritional status of bromeliads did not differ from bromeliads without ants, possibly because this ant does not have arthropod prey as a preferred food source. Our results show, for the first time, that predatory ants can translocate nutrients from one habitat to another within forests, accumulating nutrients in their feeding sites that become available to bromeliads. Additionally, we highlight that ant contribution to plant nutrition may depend on predator identity and its dietary requirements. Nest debris may be especially important for epiphytic and terrestrial bromeliads in nutrient-poor environments.     

Reproductive Caste Performs Intranidal Tasks Instead of Workers in the Ant Mystrium oberthueri

Division of labour improves the efficiency of animal societies. Efficiency is further improved in many social insects where morphologically specialized adults perform different tasks. In ants, the wingless worker caste performs non‐reproductive activities and sometimes exhibits multiple phenotypes when requirements between brood care and expert foraging diverge. Mystrium rogeri from Madagascar is a specialist predator on large centipedes, and the worker caste is highly polymorphic in size. In contrast, M. oberthueri has only large workers. The replacement of the queen caste by wingless intermorphs much smaller than workers explains this evolutionary shift in M. oberthueri. Many intermorphs occur in each colony but only a few mate and reproduce. In order to determine their contribution to non‐reproductive tasks, we performed multivariate analyses on behavioural data recorded by scan sampling from four M. oberthueri colonies in the laboratory. In unmanipulated colonies, workers and intermorphs exhibited two distinct behavioural profiles. Workers focused on guarding and foraging, while intermorphs performed brood care and nest cleaning, regardless of whether they reproduced or not. This pattern of polyethism where the reproductive caste completely takes charge of some non‐reproductive tasks is novel, as confirmed by our observations of one colony of M. rogeri where non‐reproductive tasks were restricted to workers, as in most ants. When isolated from one another, M. oberthueri workers and intermorphs developed less distinctive behavioural patterns. Some workers cared for the brood, but the intermorphs could not hunt because of their small mandibles. Such plasticity in polyethism at the colony level confers the ability to react to unexpected changes, including variable proportions of workers and intermorphs.     

Raiding and emigration dynamics in the ponerine army ant Leptogenys distinguenda (Hymenoptera, Formicidae)

Summary: Field and laboratory observations demonstrate that Leptogenys distinguenda is characterized by typical army ant behavior. Like in the "classical" army ants from the subfamilies Ecitoninae, Dorylinae and Aenictinae, raiding and emigration behavior are closely linked. The direction of raids can be altered in field experiments to a wide extent by offering ample food, suggesting it is highly influenced by the patchiness of prey. The sum of recruitments coming from one direction and the recruitment overrun are primarily responsible for the spatial development and the extension of raids. Emigration frequency can be suppressed by overfeeding a colony in the field. This result is interpreted as a secondary effect of reduced swarming activity, which gets suppressed as well in the same experiment. The discovery of a suitable nest site is considered the proximate stimulus for emigration, and the best explored areas are those that have been most thoroughly raided. As a result, emigrations are likely to lead into areas with high prey densities.     

Cryptic diversity,high host specificity and reproductive synchronization in army ant‐associated Vatesus beetles

Army ants and their arthropod symbionts represent one of the most species‐rich animal associations on Earth, and constitute a fascinating example of diverse host–symbiont interaction networks. However, despite decades of research, our knowledge of army ant symbionts remains fragmentary due to taxonomic ambiguity and the inability to study army ants in the laboratory. Here, we present an integrative approach that allows us to reliably determine species boundaries, assess biodiversity, match different developmental stages and sexes, and to study the life cycles of army ant symbionts. This approach is based on a combination of community sampling, DNA barcoding, morphology and physiology. As a test case, we applied this approach to the staphylinid beetle genus Vatesus and its different Eciton army ant host species at La Selva Biological Station, Costa Rica. DNA barcoding led to the discovery of cryptic biodiversity and, in combination with extensive community sampling, revealed strict host partitioning with no overlap in host range. Using DNA barcoding, we were also able to match the larval stages of all focal Vatesus species. In combination with studies of female reproductive physiology, this allowed us to reconstruct almost the complete life cycles of the different beetle species. We show that Vatesus beetles are highly adapted to the symbiosis with army ants, in that their reproduction and larval development are synchronized with the stereotypical reproductive and behavioural cycles of their host colonies. Our approach can now be used to study army ant‐symbiont communities more broadly, and to obtain novel insights into co‐evolutionary and ecological dynamics in species‐rich host–symbiont systems.     

Compound mimicry and trading predators by the males of sexually dimorphic Batesian mimics

Sexual dimorphism is pronounced in Myrmarachne, a large genus of ant-like jumping spiders (Salticidae) and one of the major animal groups in which Batesian mimicry of ants has evolved. Although adult females and juveniles of both sexes are distinctly ant-like in appearance, Myrmarachne males have elongated chelicerae that might appear to detract from their resemblance to ants. Experimental findings suggest that the Myrmarachne male's solution is to adopt compound mimicry (i.e. the male's model seems to be not simply an ant worker but a combination of an ant and something carried in the ant's mandibles: an "encumbered ant"). By becoming a mimic of a particular subset of worker ants, Myrmarachne males may have retained their Batesian-mimicry defence against ant-averse predators, but at the price of receiving the unwanted attention of predators for which encumbered ants are preferred prey. Two salticid species were used as predators in the experiments. Portia fimbriata is known to choose other salticids as preferred prey and to avoid unencumbered ants and their mimics (Myrmarachne females). In experiments reported here, P. fimbriata avoided encumbered ants and Myrmarachne males. Ants are the preferred prey of Chalcotropis gulosus. In our experiments, C. gulosus chose safer encumbered ants in preference to more dangerous unencumbered ants, chose Myrmarachne males more often than Myrmarachne females and showed no evidence of distinguishing between Myrmarachne males and encumbered ants. The cost of reconciling sexual dimorphism with Batesian mimicry appears to be that Myrmarachne males attract the unwanted attention of specialist predators of their compound model.