As possibly two of the last true naturalists, Carl Rettenmeyer and his wife Marian dedicated their lives to the study of army ants and their associates. Over the course of 55 years, the Rettenmeyers went on numerous field trips mainly to the Central American tropics and analyzed hundreds of self-collected samples and those sent by a multitude of other scientists, who were inspired by Carl's enthusiasm. It comes as no surprise that Carl Rettenmeyer became the world's leading expert on army ant associates. This paper, which the Rettenmeyers nearly completed before Carl's death in 2009, gives the first comprehensive list of animals known to be found in the company of a single army ant species: Eciton burchellii. The 557 recorded associates range from birds to insects and mites and comprise the largest described animal association centering around one particular species. Although some of these associates may be opportunistic encounters, we are confident that approximately 300 of the recorded species depend on the ants, at least in part, for their existence. The extinction of E. burchellii from any habitat over its vast area of distribution is likely to cause the extinction of numerous associated animals at that site. This overview will hopefully inspire researchers throughout the world to follow in the Rettenmeyers' footsteps and continue the investigation of army ants and their associates.

In a recent study, Denny et al. (2004a) showed that queens of the army ant, Eciton burchellii, mate with multiple males and presented estimates suggesting that they mate with more males than queens of any other ant species so far investigated. They also inferred that data were consistent with queens being inseminated repeatedly throughout their life, which would be exceptional among the social Hymenoptera and contradictory to predictions from kin selection theory. In the present study, we reanalyze these data using new software and supplement them with similar microsatellite data from other colonies of the same species. Mating frequencies in E. burchellii are indeed very high (mean observed and effective queen-mating frequencies of 12.9 each) but considerably lower than the previous estimates. We show that the number of patrilines represented in the first worker offspring of a young queen is lower than in older queens but suggest that this may be due to initial sperm clumping in the queen's sperm storage organ, rather than to repeated inseminations. Moreover, we found no evidence for repeated mating by genotyping sequential worker generations produced by a single old queen, showing that she did not obtain new inseminations despite ample opportunities for mating.

Army ants have been studied thoroughly for more than a century. The conduction of column and swarm mass raids, featured by epigaeicly active species, is believed to be a central characteristic of army ant behavior. Most army ant species, however, lead a hypogaeic life. Due to the difficulties to observe them, nothing is known about their hypogaeic behavior in the field. Using palm oil baits, trail excavations, and laboratory observations, the hypogaeic foraging of Dorylus (Dichthadia) laevigatus was observed in Malaysia. D. laevigatus was found to construct stable hypogaeic trunk trail systems providing quick and easy access to all parts of its foraging area. Small column raids were conducted throughout the ground stratum and above the ground surface. These raids were caste specific, with the smallest workers predominantly following existing cracks and tunnels in the soil. In case of food location, larger workers were recruited from nearby trunk trails. Exploratory trails leading to prey had to be widened before larger workers could gain access and help to process the food. Bulky food sources such as baits or termite mounds could be exploited over several weeks to months. Besides raiding in columns, D. laevigatus came occasionally to the ground surface at night to conduct swarm raids. This combination of swarm and column raids with the use of trunk trails has never been demonstrated for a classical army ant species. The omnipresence of D. laevigatus within its foraging area stands in sharp contrast to epigaeicly active species, characterized by a very localized and temporary presence at foraging sites. D. laevigatus stayed in the same foraging area for several weeks to months. Having a broad diet and the ability to exploit bulky food sources over long periods of time, D. laevigatus seems to follow a sustainable use of the soil fauna. Summing up these particularities demonstrates a remarkable divergence of the hypogaeic foraging of D. laevigatus from that of epigaeicly foraging army ant species.

The army ant Eciton burchellii is probably the most important arthropod predator in the Neotropics, and many animal species depend upon it. Sex‐biased dispersal with winged males and permanently wingless queens may render this species especially sensitive to habitat fragmentation and natural barriers, which might have severe impacts on population structure and lead to population decline. Using nuclear microsatellite markers and mitochondrial sequences, we investigated genetic differentiation in a fragmented population in the Panama Canal area. While nuclear markers showed little differentiation between subpopulations (FST = 0.017), mitochondrial differentiation was maximal in some cases (ΦST = 1). This suggests that, while females are not capable of crossing barriers such as large rivers, flying males are able to promote nuclear gene flow between the studied forest patches. Consistent with this interpretation, we did not find any evidence for inbreeding or genetic deterioration on Barro Colorado Island over the last 90 years since its formation.

We show that ants can reconnoitre their surroundings and in effect plan for the future. Temnothorax albipennis colonies use a sophisticated strategy to select a new nest when the need arises. Initially, we presented colonies with a new nest of lower quality than their current one that they could explore for one week without a need to emigrate. We then introduced a second identical low quality new nest and destroyed their old nest so that they had to emigrate. Colonies showed a highly significant preference for the (low quality) novel new nest over the identical but familiar one. In otherwise identical experiments, colonies showed no such discrimination when the choice was between a familiar and an unfamiliar high-quality nest. When, however, either all possible pheromone marks were removed, or landmarks were re-orientated, just before the emigration, the ants chose between identical low-quality new nests at random. These results demonstrate for the first time that ants are capable of assessing and retaining information about the quality of potential new nest sites, probably by using both pheromones and landmark cues, even though this information may only be of strategic value to the colony in the future. They seem capable, therefore, of latent learning and, more explicitly, learning what not to do.