Reproductive physiology, dominance interactions, and division of labour among bumble bee workers

Abstract. Bumble bee workers (Bombus bifarius, Hymenoptera: Apidae) exhibit aggression toward one another after the colony begins producing female reproductive offspring (the competition phase). Workers in competition phase colonies must continue to perform in‐nest tasks, such as nest thermoregulation, and to forage for food, to rear the reproductives to maturity. Therefore, competition phase workers are faced with potentially conflicting pressures to work for their colonies, or to compete for direct reproduction. The effects of reproductive competition on worker task performance were quantified by measuring relationships of worker body size, reproductive physiology, and aggression with their rates of task performance. If worker division of labour was strongly affected by competition, it was predicted that fecund workers would avoid performing nest maintenance and foraging tasks, focusing instead on reproductive behaviour. Furthermore, it was predicted that fecund workers would dominate their nest mates, and that subordinate workers would perform nonreproductive tasks at higher rates. Worker aggression was associated closely with direct reproductive competition. Both aggression and brood interaction rates were related positively with ooctye development. Furthermore, foraging was associated negatively with ovarian development. However, in‐nest and foraging task performance rates were not associated with social aggression. The results support a partial role for reproductive competition in worker polyethism. Although worker aggression did not directly affect polyethism, reproductively competent workers avoided foraging tasks that would remove them from egg‐laying opportunities. Reproductively competent workers did perform in‐nest tasks, suggesting that these tasks entail little cost in terms of reproductive competition.     

<Emphasis Type="Italic">Polistes japonicus</Emphasis> (Hymenoptera,Vespidae) queens monopolize ovipositing but are not the most active aggressor in dominant-subordinate interactions

In order to elucidate the dominant–subordinate relationship between the foundress and workers, five colonies of the paper wasp Polistes japonicus were observed in a netted and covered cage located outdoors. The number of workers in each colony ranged from four to eight. Workers were divided into first and second broods. Abdominal wagging and ovipositing were performed almost exclusively by the foundress throughout colony development. However, an analysis of aggressive encounters indicated that although the foundress hardly received dominance behaviors (aggression) from workers, it lacked either partially or completely the following characteristics of the queen that are usually seen in paper-wasp colonies with independent-founding queens (except in one colony that produced no second brood): the queen being socially dominant over any worker (the queen had more wins than losses in one-on-one dominance contests with any worker), exhibiting the highest frequency of dominance behaviors, and directing dominance behaviors primarily toward the socially most-dominant worker. In particular, during the mixed-brood period (when all first- and second-brood workers were present on the nest) the foundress hardly exhibited dominance behaviors toward socially dominant workers (mainly second brood) but frequently directed dominance behaviors toward socially subordinate workers (mainly first brood). The foundress disappeared in two colonies before the reproductives emerged; in these colonies the socially most-dominant worker inherited the colony and laid many eggs. The frequency of abdominal wagging by these two foundresses decreased during colony development, while it did not in the other colonies. This suggests that abdominal wagging provides information about the vigor of the performer. The superseder was socially dominant over all other workers, but spent little time wagging its abdomen and allowed some workers to lay eggs.     

Dominance hierarchy among workers changes with colony development in Polistes japonicus (Hymenoptera, Vespidae) paper wasp colonies with a small number of workers

Dominance hierarchy in the primitively eusocial wasp Polistes japonicus was analysed in four colonies for two periods: (1) the first-brood period, when only early emerging workers are present on the nest, and (2) the mixed-brood period, when the first and second (last) broods are present on the nest. The rank in the dominance hierarchy was determined based on a sociogram showing a dominance–subordinance relationship for all pairs of workers. During the first-brood period, older workers were likely to be more dominant (older dominance hierarchy), while the rank of workers was reversed during the mixed-brood period, with younger workers being likely to be more dominant (younger dominance hierarchy). However, the oldest and youngest workers were not always the top-ranked workers in the dominance hierarchy during the first- and mixed-brood periods, respectively, and during the mixed-brood period no younger dominance hierarchy was evident when the first or second brood was analysed separately. Higher ranked workers displayed dominance behaviour more frequently, and the lowest ranked worker hardly displayed dominance behaviour. Most workers displayed dominance behaviours primarily towards the worker ranked immediately below in the dominance hierarchy during the mixed-brood period but not during the first-brood period. The bodies of younger workers were larger for the mixed brood, but not for the first brood in some colonies or the second brood in all colonies. The association between body size and rank in the dominance hierarchy was negative during the first-brood period and positive during the mixed-brood period, with a nearly significant trend also seen even when the analysis was limited to the second brood. To explain the above temporal change from an older dominance hierarchy to a younger dominance hierarchy, we propose the hypothesis that the probability of a worker inheriting the colony increases rapidly with colony development, and consequently younger larger workers attempt to move up the dominance hierarchy in order to produce their own offspring by becoming the superseder late in colony development, rather than working harmoniously so as to boost the overall production of reproductive progeny for a colony, which is the strategy adopted early in colony development.     

Polymorphism and Division of Labor During Foraging Cycles in the Leaf-cutting Ant <Emphasis Type="Italic">Acromyrmex octospinosus</Emphasis> (Formicidae; Attini)

While division of labor within leaf-cutting ant nests has been well-characterized in the context of the collection and processing of leaf material, environmental factors such as day-night cycles and heavy rainfall limit the time during which leaf-cutting ant workers leave the nest to gather forage. Using a novel “flat panel” nest design, we studied how patterns of within-nest task performance changed when a colony of the leaf-cutting ant Acromyrmex octospinosus was and was not provided access to forage. We conducted scan samples of individuals working within the nest under both conditions and compared task allocation patterns across provisioning regimes and between workers of different sizes. When labor was compared between worker size groups, “minor” workers (head width ≤2.0 mm) and “major” workers (head width >2.0 mm) showed significantly different task performance patterns when forage was available: minors performed mostly brood-care and garden maintenance, while majors were mostly involved in the handling of freshly-cut leaf fragments. In contrast, when the colony was deprived of forage, the task performance patterns of minor and major workers converged and did not significantly differ. Marked major workers known to be foragers tended to remain idle within the nest when the colony was deprived of forage, while non-foragers of similar head width engaged in a variety of within-nest tasks, suggesting polyethism in majors may be based on factors other than size.     

The role of competition in task switching during colony emigration in the ant Leptothorax albipennis

The decision-making process that determines when an animal should switch between tasks is a fundamental issue in the study of animal behaviour. We investigated, for the first time, such task switching in terms of the dynamics of worker populations in ant colonies. During colony emigration in the ant Leptothorax albipennis, the colony has to carry out the following three tasks: (1) transport of brood and nestmates to the new nest; (2) sorting of the brood into its characteristic pattern; and (3) building the nest wall. At the beginning of the emigration, the stimuli for all three tasks increase simultaneously but the tasks are performed sequentially by populations of workers in the colony. The issue here is how decision making at the colony level is based on the behaviour of individual workers. We used a mathematical model to explore the hypothesis that such colony level task switching is based on tasks competing for workers. The essential feature of this model is that the sequence of tasks performed by an individual worker need not match the sequence of tasks on which the colony concentrates. We base the parameterization of our model on our detailed experimental study of eight emigrations, one for each of eight L. albipennis colonies. We compared our results with earlier work that emphasizes the role of response thresholds in task-related decisions. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Multiple breeders, breeder shifts and inclusive fitness returns in an ant

In social insects, colonies may contain multiple reproductively active queens. This leads to potential conflicts over the apportionment of brood maternity, especially with respect to the production of reproductive offspring. We investigated reproductive partitioning in offspring females (gynes) and workers in the ant Formica fusca, and combined this information with data on the genetic returns gained by workers. Our results provide the first evidence that differential reproductive partitioning among breeders can enhance the inclusive fitness returns for sterile individuals that tend non-descendant offspring. Two aspects of reproductive partitioning contribute to this outcome. First, significantly fewer mother queens contribute to gyne (new reproductive females) than to worker brood, such that relatedness increases from worker to gyne brood. Second, and more importantly, adult workers were significantly more related to the reproductive brood raised by the colony, than to the contemporary worker brood. Thus, the observed breeder shift leads to genetic benefits for the adult workers that tend the brood. Our results also have repercussions for genetic population analyses. Given the observed pattern of reproductive partitioning, estimates of effective population size based on worker and gyne samples are not interchangeable.     

Changing colony growth rates inCamponotus floridanus as a behavioral response to conspecific presence (Hymenoptera: Formicidae)

Previous work with the antCamponotus floridanus demonstrated that perception of competition can be clearly differentiated from effects of mortality and decreased resources. That is, brood biomass in ant colonies decreases as a consequence of a behavioral decision(s) rather than because of limited food availability or reduced numbers of brood tenders. The experiments presented here extend that work. Under experimental conditions, colony growth inC. floridanus is modified by distance between brood and unrelated conspecifics and by worker age distribution. When nonnestmates are encountered at the nest versus at a separate foraging site, less brood is maintained by a colony. Although colonies with older workers maintain a brood biomass similar to that of colonies with younger workers, that biomass is concentrated in fewer, larger, more rapidly maturing larvae. These effects seem to be due entirely to worker control.     

Sociometry and sociogenesis of colonies of the harvester ant, Pogonomyrmex badius: distribution of workers, brood and seeds within the nest in relation to colony size and season

1. The vertical distribution in the nest of chambers, workers, callow workers, brood and seeds was studied in the harvester ant, Pogonomyrmex badius, in northern Florida. On each of four sample dates (May, July, October, January), six to seven colonies, chosen to represent the full range of sizes, were excavated. All chamber contents were collected and counted. Chambers were mapped and measured. In a preliminary study, two nests were excavated after preventing vertical migration by driving barriers into the wall of a pit next to the nest, severing the vertical tunnels. The vertical distribution of these barrier-nests differed little from unrestrained nests, indicating that unrestrained excavation produced a reasonable picture of vertical distributions. 2. Nest depth, chamber number and total area increased with colony size. Chamber area declined sharply with depth, as did chamber number, such that more than half of the total area was found in the upper quarter of the nest. 3. The proportion of dark-coloured (older) workers also declined strongly with depth, but this decline was weaker in the spring, and depended to a modest degree on colony size. Conversely, in the distribution of callow (young) workers, the proportion increased towards the bottom of the nest. Mean worker age was inversely related to the depth at which workers were found. The proportion of the brood also increased towards the bottom of the nest, with worker brood, sexual brood, pupae and larvae all being distributed similarly. 4. By contrast, seeds were stored at a preferred absolute depth between 40 and 100 cm. Colonies shallower than 100 cm stored seeds in their deepest chambers. Larger colonies stored most seeds in the upper third of the nest, but patterns were somewhat erratic because chambers were either filled completely with seeds or were empty. 5. Because chamber area decreased sharply with depth, the densities (individuals cm^–2) of all colony members, including dark workers, were lowest near the surface and highest in the deepest parts of the nest. Here, worker densities ranged from 2 to 8 cm^–2, and brood from 2 to 25 cm^–2. 6. The regularity of the patterns of distribution suggests that harvester ant colonies have considerable spatial and temporal structure, which serves or is the outcome of important colony processes. A simple mechanism that could generate several of these patterns is discussed. New workers produced deep in the nest move upwards as they age. As they leave the brood zone they change from brood care to general nest duties, including increased nest excavation, leading to the top-heavy pattern of nest area. As they appear at the surface, they change to guarding and foraging. Thus, age polyethism may be partly the result of this upward migration of workers.     

Intracolonial conflict in the slave-making ant <Emphasis Type="Italic">Protomognathus americanus</Emphasis>: dominance hierarchies and individual reproductive success

Summary Social group viability results from a trade-off between cooperation and conflict, driven respectively by group and individual interests. Workers of the slave-making ants are known to have a high egg-laying potential, leading to a potential conflict over male production. Queenright and queenless nests of the slave-making ant Protomognathus americanus show a near-linear dominance hierarchy, and dominance rank is correlated with reproductive activity. Genetic and behavioural analysis revealed that the queen, when present in the nest, is behaviourally dominant and monopolises reproduction. In queenless nests, the haploid (male) brood is produced primarily by a single worker. We suggest the dominance hierarchy regulates male production, between the queen and her workers as well as among workers. Comparison of our results to another study allows us to place our data in an ecological context. This slave-making ant species appears to fit the concession model of reproductive skew: where resources (i.e. host nests) are poor, there is strong skew and where resources are richer reproduction is more egalitarian.Received 31 July 2003; revised 7 October 2003; accepted 9 October 2003.     

Altruism and relatedness at colony foundation in social insects

Cooperative nest initiation in social insects is most easily explained when cooperating females are relatives, as is common in polistine wasps. However, recent research has revealed that unrelated ant queens also initiate colonies together. Reproductive dominance hierarchies are absent among unrelated foundresses, which contrasts with the rigid dominance hierarchies found among related foundresses. New field studies of joint nest founding among non-relatives show that cooperation is favored where colonies are clumped and brood raiding is common, so that attaining a large worker force quickly is critical to colony survival. These studies enrich our understanding of the role of relatedness in social groups.     

Foraging decisions of individual workers vary with colony size in the greenhead ant Rhytidoponera metallica (Formicidae, Ectatomminae)

Summary. The ability of worker ants to adapt their behaviour depending on the social environment of the colony is imperative for colony growth and survival. In this study we use the greenhead ant Rhytidoponera metallica to test for a relationship between colony size and foraging behaviour. We controlled for possible confounding ontogenetic and age effects by splitting large colonies into small and large colony fragments. Large and small colonies differed in worker number but not worker relatedness or worker/brood ratios. Differences in foraging activity were tested in the context of single foraging cycles with and without the opportunity to retrieve food. We found that workers from large colonies foraged for longer distances and spent more time outside the nest than foragers from small colonies. However, foragers from large and small colonies retrieved the first prey item they contacted, irrespective of prey size. Our results show that in R. metallica, foraging decisions made outside the nest by individual workers are related to the size of their colony.Received 23 March 2004; revised 3 June 2004; accepted 4 June 2004.     

The economics of brood raiding and nest consolidation during ant colony founding

Summary The most dangerous time for an ant colony is during the founding stage when the small colony is vulnerable to predation and competition. Colonies can grow more rapidly when multiple queens cooperate in raising the first worker brood (pleometrosis) or by raiding other incipient colonies for their brood. This brood raiding has been proposed to be the primary force selecting for pleometrosis, i.e. multiple-queen colonies may have a considerable advantage in destroying neighbours by aggressively stealing their brood. An alternative hypothesis is that incipient nests are part of a larger, interconnected population structure and that brood raiding reflects cooperative pleometrosis with subdivided colonies. A simple mathematical model supports the second hypothesis: workers of incipient colonies are especially favoured to peaceably abandon their nest and join with other colonies if the queens are related or queens from raided colonies can infiltrate the raiding colony. The latter condition is often met in ant species that brood raid and particularly exemplified in fire ants (Solenopsis invicta), where brood raiding involves little mortal combat and combines with pleometrosis to rapidly increase colony size. It is proposed that the term nest consolidation should replace brood raiding to more accurately reflect the relatively non-aggressive and potentially apparently cooperative nature of interactions between incipient ant colonies.     

Flexible task allocation and the organization of work in ants

Flexibility in task performance is essential for a robust system of division of labour. We investigated what factors determine which social insect workers respond to colony-level changes in task demand. We used radio-frequency identification technology to compare the roles of corpulence, age, spatial location and previous activity (intra-nest/extra-nest) in determining whether worker ants (Temnothorax albipennis) respond to an increase in demand for foraging or brood care. The less corpulent ants took on the extra foraging, irrespective of their age, previous activity or location in the nest, supporting a physiological threshold model. We found no relationship between ants that tended the extra brood and corpulence, age, spatial location or previous activity, but ants that transported the extra brood to the main brood pile were less corpulent and had high previous intra-nest activity. This supports spatial task-encounter and physiological threshold models for brood transport. Our data suggest a flexible task-allocation system allowing the colony to respond rapidly to changing needs, using a simple task-encounter system for generalized tasks, combined with physiologically based response thresholds for more specialized tasks. This could provide a social insect colony with a robust division of labour, flexibly allocating the workforce in response to current needs.     

Proximate Determinants of Reproductive Skew in Polygyne Colonies of the Ant Formica fusca

Understanding the determinants of reproductive skew (the partitioning of reproduction among co‐breeding individuals) is one of the major questions in social evolution. In ants, multiple‐queen nests are common and reproductive skew among queens has been shown to vary tremendously both within and between species. Proximate determinants of skew may be related to both queen and worker behaviour. Queens may attempt to change their reproductive share through dominance interactions, egg eating and by changing individual fecundity. Conversely, workers are in a position to regulate the reproductive output of queens when rearing the brood. This paper investigates queen behaviour at the onset of egg laying and the effect of queen fecundity and worker behaviour on brood development and reproductive shares of multiple queens in the ant Formica fusca. The study was conducted in two‐queen laboratory colonies where the queens produced only worker offspring. The results show that in this species reproductive apportionment among queens is not based on dominance behaviour and aggression, but rather on differences in queen fecundity. We also show that, although the queen fecundity at the onset of brood rearing is a good indicator of her final reproductive output, changes in brood composition occur during brood development. Our results highlight the importance of queen fecundity as a major determinant of her reproductive success. They furthermore suggest that in highly derived polygyne species, such as the Formica ants, direct interactions as a means for gaining reproductive dominance have lost their importance.     

Dynamics of colony emigration in the ant Aphaenogaster senilis

In many social insect species, colonies frequently emigrate to a new nest. This requires the coordination of many individuals, and it puts the queen at risks of being lost or predated. We experimentally studied colony emigration in the ant Aphaenogaster senilis, who emigrates frequently and obligatorily reproduces by colony fission. As in other species, colony emigration was characterised by a synchronised relocation of workers. Foragers found the new nest site and triggered the relocation of the “inside” workers, which built up following a sigmoid curve. Unlike in Temnothorax, where workers are transported to the new nest, most individuals relocated by walking. The brood was transported around the middle of colony relocation, mostly by “inside” workers because they represent most of the workforce. The queen walked to the new nest at the middle of colony relocation, when the flow of ants to the new nest was maximal. Overall, this temporal dynamic of colony emigration is similar to that observed in other species. However, we argue that species-specific traits, such as whether workers are transported to the new nest or relocate by themselves, may affect parts of the process of colony emigration.     

How brood influences caste aggregation patterns in the dimorphic ant species Pheidole pallidula

Spatial distribution of ant workers and, notably their aggregation/segregation behaviour, is a key-element of the colony social organization contributing to the efficiency of task performance and division of labour. In polymorphic species, specialized worker castes notably differ in their intrinsic aggregation behaviour. In this context, knowing the preponderant role of minors in brood care, we investigate how a stimulus such as brood can influence the spatial patterns of Pheidole pallidula worker castes. In a homogeneous area without brood, it was shown that minors display only a low level of aggregation while majors form large clusters in the central area. Here we find out that these aggregation patterns of both minors and majors can be deeply influenced by the presence of brood. For minors, it nucleates or enhances the formation of a large stable cluster. Such high sensitivity of minors to brood stimuli fits well with their role as main brood tenders in the colony. For majors, interattraction between individuals still remains the prevailing aggregation factor while brood strongly influences the localisation of their cluster. We discuss how the balance between interattraction and sensitivity to environmental stimuli determines the mobility of each worker castes and, consequently, the availability of minors and majors to participate in everyday colony tasks. Moreover, we will evoke the functional value of majors’ cluster location close to the brood, namely with respect to social regulation of the colony caste ratio. Received 30 May 2005; revised 11 January 2006; accepted 13 January 2006.     

Gene expression patterns associated with caste and reproductive status in ants: worker‐specific genes are more derived than queen‐specific ones

Variation in gene expression leads to phenotypic diversity and plays a central role in caste differentiation of eusocial insect species. In social Hymenoptera, females with the same genetic background can develop into queens or workers, which are characterized by divergent morphologies, behaviours and lifespan. Moreover, many social insects exhibit behaviourally distinct worker castes, such as brood‐tenders and foragers. Researchers have just started to explore which genes are differentially expressed to achieve this remarkable phenotypic plasticity. Although the queen is normally the only reproductive individual in the nest, following her removal, young brood‐tending workers often develop ovaries and start to reproduce. Here, we make use of this ability in the ant Temnothorax longispinosus and compare gene expression patterns in the queens and three worker castes along a reproductive gradient. We found the largest expression differences between the queen and the worker castes (~2500 genes) and the smallest differences between infertile brood‐tenders and foragers (~300 genes). The expression profile of fertile workers is more worker‐like, but to a certain extent intermediate between the queen and the infertile worker castes. In contrast to the queen, a high number of differentially expressed genes in the worker castes are of unknown function, pointing to the derived status of hymenopteran workers within insects.     

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.     

The Use of the Vibration Signal and Worker Piping to Influence Queen Behavior during Swarming in Honey Bees, Apis mellifera

We investigated worker regulation of queen activity during reproductive swarming by examining the rates at which workers performed vibration signals and piping on queens during the different stages of the swarming process. Worker–queen interactions were first examined inside observation hives during the 2–3 wk that preceded the issue of the swarm (pre‐swarming period) and then inside the swarm clusters during the period that preceded liftoff and relocation to a new nest site (post‐swarming period). Queen court size did not differ between the pre‐ and post‐swarming periods, but workers fed the queens less inside the swarm clusters. Workers performed vibration signals on the queens at increasing rates throughout the pre‐swarming period inside the natal nest, but rarely or never vibrated the queen inside the swarm. Piping was performed on the queens during both the pre‐ and post‐swarming periods and always reached a peak immediately before queen flight. During the final 2–4 h before swarm liftoff, queens were increasingly contacted by waggle dancers for nest sites, some of which piped the queen. The vibration signal may operate in a modulatory manner to gradually prepare the queen for flight from the natal nest, and the cumulative effects of the signal during the pre‐swarming period may make further vibrations on the queen unnecessary when inside the swarm cluster. In contrast, worker piping may function in a more immediate manner to trigger queen takeoff during both the pre‐ and post‐swarming periods. Workers that vibrate and pipe the queen tend to be older, foraging‐age bees. The regulation of queen activity during colony reproduction may therefore be controlled largely by workers that normally have little contact with queens, but help to formulate colony reproductive and movement decisions.     

The role of anchor-tipped larval hairs in the organization of ant colonies

The spatial organization within a social insect colony is a key component of colony life. It influences individual interaction rates, resource distribution, and division of labor within the nest. Yet studies of social insect behavior are most often carried out in artificial constructions, which may change worker behavior and colony organization. We observed how workers of the ant Pheidole rhea organized brood in nests with deep chambers and textured walls that were designed to mimic their natural constructions more closely. Instead of clumping larvae into piles on the chamber floor, workers suspended fourth-instar larvae from the vertical walls and ceiling of each chamber while young larvae and pupae were clumped at the base. Fourth-instar larvae possess five rows of anchor-tipped hairs on their dorsal side, and we predicted that these hairs functioned to attach larvae to the nest walls. We gave larvae "haircuts," where only the anchor-tipped hairs were removed, and then tested their ability to adhere to a textured surface raised to an angle of 90° and then 120° with respect to the horizontal plane. Larvae whose hairs had been clipped came unattached in almost all trials, while larvae whose hairs remained intact stayed attached. This confirmed that anchor-tipped hairs functioned to attach larvae to the walls of the nest. The presence of anchor-tipped hairs is widespread and has been documented in at least 22 genera from the ant subfamily Myrmicinae, including species that occur in a variety of environments and represent a broad range of nesting habits. Based on our results, it is likely that many species exhibit this larval hanging behavior, and this could impact colony characteristics such as spatial organization and the care of developing larvae by nurse workers.