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.
A new method employing palm oil as bait was developed for studying the distribution and ecology of subterranean army ants. In SE Asia the hypogaeic army ant Dorylus laevigatus was found to be very common in both forested and open environments. More than 10 000 workers were found at individual baits. The workers cooperatively dig a three-dimensional tunnel network into the soil. Over a period of 72 days no emigrations of D. laevigatus could be detected, a first indication of a facultatively stationary way of life in this ant. Encounters with Pheidologeton silenus about food resources were observed. In feeding experiments D. laevigatus readily took a variety of arthropods and annelids but ignored starch containing vegetables as food. The rare hypogaeic D. (Alaopone) cf. vishnui could be collected for the first time in India and Sri Lanka. Also the epigaeic D.(Anomma) nigricans from Africa were found to be attracted to palm oil. The oil-method thus provides the opportunity to detect and monitor populations of army ants of the genus Dorylus in tropical and subtropical habitats.
We report the first experimental evidence of seed collecting behavior in an ant-garden-inhabiting ant species in the Palaeotropics.Vascular epiphytes growing on the giant bamboo Gigantochloa scortechinii (Poaceae) were collected at Ulu Gombak, West Malaysia. Sixteen epiphyte species were growing in carton-nests of seven ant species. All epiphytes on bamboo were associated with ants. The most frequent ant species (Crematogaster sp.1, Myrmicinae) apparently nests only on bamboo. It was tested for its behavior towards the seeds of three epiphyte species (Dischidia nummularia (Asclepiadaceae), Aeschynanthus fecundus, Aeschynanthus albidus (Gesneriaceae)) and one non-epiphyte species (Emilia sonchifolia (Asteraceae)). Most of the offered epiphytes' seeds were carried to the nest, while the seeds of the non-epiphyte were ignored or even discarded. There were no speciesspecific differences among the epiphytes' seeds.We hypothesize that seed-collecting behavior is necessary for the establishment of ant-garden associations and for the colonization of bamboo culms by epiphytes. The smoothsurfaced and relatively short-lived bamboo culms would not host epiphytes without the mediation of the ants. We suspect that ants may also have a great influence on the distribution of epiphytes on other hosts.In this paper we describe ants as active nest builders and seed collectors that give certain epiphytes the opportunity to live in open and sun exposed habitats on bamboo. Benefits to the ants are discussed as well.
Epigaeicly active species have set the standards for our understanding of army ant behavior. However, the majority of species leads a cryptic hypogaeic life. Being the first of the hypogaeicly foraging and nesting army ant species investigated in more detail, we studied the nesting habits and colony structure of Dorylus (Dichthadia) laevigatus in
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