Wandering ants

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Driver ants ( Dorylus sp.) With a captured grasshopper in Cameroon

As wandering ants , also called driver ants or army ants , ant species are summarized, which all exhibit a group of common, interlinked behaviors, the "driver ant syndrome" (English "army ant syndrome"). Most species with this behavioral syndrome form a group of related subfamilies, the Dorylomorpha. In addition, it occurs less frequently in a number of other species that are not closely related and belong to different subfamilies. Other species display only some, but not all, of the characteristic behaviors.

The driver ant syndrome

The following behaviors are characteristic of the driver ants:

  • Hunting only in groups. Typical for ants is a swarming of individual scouts who recruit additional workers to help out when they discover food. In the case of wandering ants, the hunt takes place right from the start in groups, which go out together as "military campaigns". These can include hundreds of thousands of individuals. The armies are permanently connected to the nest by individuals running back and forth.
  • Periodic relocation of the nest location. Wandering ants have a nest or an above-ground location known as a bivouac , to which they return after their raids. However, this nest will be relocated after a certain time and the entire colony will move to a new location. Other species of ants can also move their nests, but usually only do so in the event of external disturbances.
  • Wandering ants reproduce exclusively via wingless queens by splitting or budding the mother colony. The young queen moves out with some of the workers from her mother colony. New colonies are not established by the independent nesting of a queen with her own offspring.
  • The queens of the wandering ant species are always particularly large in relation to the workers. Your abdomen is swollen and swollen (" physogastric ") to accelerate egg production .

These behaviors are interlinked. Group hunting is considered the starting point and origin of the behavioral syndrome. Hunting in groups can overwhelm particularly large and defensive prey. In addition, colonies of other social insects, which are often well defended and defensible, can be overcome and captured. However, through group hunting, the food base near the nest is exhausted more quickly; this will force the move. Since a large number of workers have to cooperate from the beginning for successful group hunting, the individual nesting must also be given up.

Other common traits are found in many, but not all, wandering ants. Many species have an extreme size polymorphism of workers with workers of different body sizes, which sometimes develop sharply divided lower castes. Most of them have only one queen, in spite of the great strength of the population, which can include millions of individuals. Many species also have complex life cycles in which stationary reproductive and mobile migration phases alternate in a regular manner.

The "real" wandering ants

Three related subfamilies of ants , the Ecitoninae , Dorylinae and Aenictinae , combined to form the Dorylomorpha, are referred to as actual wandering ants . In the New World only the Ecitoninae occur, in the Old World the Dorylinae and Aenictinae. In the case of wandering ants, a state can in extreme cases contain several million animals. The African wandering ant Dorylus wilverthi forms states with more than 20 million individuals. Without exception, all species in this kin group show complete driver ant syndrome as far as their biology is known.

Other wandering ants

Outside of this kinship group there are some species that show the same behavior pattern in more or less perfect expression. All elements are e.g. B. found in some species of the genus Leptogenys (subfamily Ponerinae) and the genus Pheidologeton (subfamily Myrmicinae), both of which live in tropical East Asia. Other genera for which comparable behaviors have been reported are e.g. B. Cerapachys , Leptanilla , Onychomyrmex , Pachycondyla . Usually, however, individual behaviors are different here. So hunt z. For example, many Leptogenys species are not collected collectively from the start, but are recruited by scouts, but change nesting locations regularly. Obligatory group hunting, but no change in nesting location, has been reported for some pheidologic species.

Occurrence

The distribution area of ​​the wandering ants extends over the tropics and subtropics of the Old World as well as the New World. They are common in Africa , Asia , South America and Central America .

Nomadic and stationary phase

Wandering ants have two different phases of activity: a nomadic (wandering) phase and a stationary phase. These alternate regularly with the South American Eciton species. In most other migratory ants, the phases merge more into one another.

Nomadic phase

In the nomadic phase, the ants migrate during the day, prey on insects , spiders and small vertebrates, and when dusk falls they form their nests, which they change almost daily. For some species, the hiking trails are secured by soldiers. During their hunt, they are accompanied by birds of various species, such as ant birds and specialized thrush and wren species that devour the frightened insects. Among the wandering ants there are also species that only appear at night. There are insufficient studies of their activity. Among the wandering ants, the diurnal species Eciton burchelli and Eciton hamatum are the most studied representatives.

Stationary phase

The stationary phase, which lasts around two to three weeks, begins when the larvae pupate. Now the prey previously fed to the larvae are only given to the queen. The queen's abdomen ( gaster ) swells up, called physogastry , and the eggs are laid. At the same time as the larvae hatch, the new workers leave their cocoons and the wandering ants then resume their nomadic migration phase.

Nest building

The Eciton species do not build a nest at all like most ants, but rather form a living nest with their bodies, which is called a "bivouac" in technical language. Bivouacs are in a protected location, e.g. B. applied to tree trunks. The members hold each other's legs and form a kind of ball that appears unstructured to laypeople, but represents a well-structured structure. The older workers are on the outside; inside are the younger workers. In the event of the slightest disturbance, soldiers gather on the surface of the bivouac to defend the nest, armed with strong jaws and (in the case of the Aenictinae and Ecitoninae) with spikes. The nest is criss-crossed with numerous corridors and contains several chambers with food, the queen and the larvae and eggs. Other wandering ants usually build earth nests in which, however, bivouac-like aggregations can occur.

Food and raids

food

Wandering ants can prey on many prey a day and have a significant influence on the occurrence, diversity and behavior of their prey. The range of prey is very different for the individual species. Subterranean species primarily prey on articulated animals living in the ground and their larvae, earthworms, and occasionally young vertebrate animals, turtle eggs or oily seeds. Most of the species have specialized in breeding other ants and wasps (the column predators). Only the few species with large swarm forays seem to have a really wide range of food. Even so, these species do not prey on and eat every animal. While smaller vertebrates that get caught in the raids are also killed, the jaws of the American Eciton species, in contrast to the African Dorylus species, are not suitable for dividing this prey. (It is left lying around and used by scavengers or flies accompanying swarms.) Only a few species hunt above the surface of the earth, where they primarily look for prey in the leaf litter and lower vegetation. There are also about five species hunted in higher trees, which can attack birds and eggs there, but mostly prey on other state-forming insects and their eggs and larvae.

Raids

Tropical Army Ant ( Eciton burchelli ) soldier with distinctive biting tools (illustration)

The wandering ants use two patterns in their raids: crevice raids and swarm raids. The species Eciton hamatum is a typical representative of crevice attacks. During the raids, the swarm members separate to the side of the main route and form small searching groups, similar to a tree with its branches. The individual side paths can have a large distance from one another. Eciton burchelli chooses the swarm raid. It also has a main route at the beginning, which is then divided into many branches like an umbel , but the individual side paths are close together and cross over several times, so that the individual troops cover a larger area more effectively. The column can fan out to up to 20 meters.

Genera and species (selection)

The driver ants number around 150 species in the New World and around 100 species in the Old World.

Distribution: Mainly Asia, but also several African species. The subfamily is represented by a genus Aenictus . The genus is characterized by the lack of large morphological differences (e.g. there are no soldiers or significantly smaller workers). The majority of the species live underground, with some species active above ground.

Distribution: Mainly Africa; about five Asian species, one of them to southern Europe. The subfamily is represented by a genus Dorylus . This is in turn divided into five sub-genera: Anomma , Dichthadia , Dorylus , Rhogmus and Typhlopone .

  • Dorylus (Anomma) wilverthi and D. (A.) nigricans are the most popular African driver ants that hunt above ground.
  • Dorylus (Dichthadia) laevigatus lives in Asia and is the most original species of the genus.

Distribution: Southern states of the USA via Central America to Argentina. The subfamily is divided into five genera:

  • Cheliomyrmex . This is the most original genus of the subfamily. Due to the purely subterranean occurrence, little is known about the way of life of the known species.
  • Eciton . This is probably the best-known genus of driver ants, as there have been many studies on the biology and behavior of the above-ground hunting species Eciton burchellii and Eciton hamatum .
  • Labidus . In this genus, Labidus praedator , an above-ground type of driver ant, also occurs. Although not necessarily rarer, the other species are less noticeable due to their more hidden way of life.
  • Neivamyrmex . This genus is represented by a large number of mostly very small species, about whose biology, due to their predominantly subterranean way of life, little is known.
  • Nomamyrmex . With only two species with four subspecies, this is the species-poorest driver ant genus. Are described in N. esenbeckii ( N. e. Crassicornis , N. e. Mordax , N. e. Wilsoni ) and N. hartigii .

behavior

The phenomenon of the ant mill is particularly observed in wandering ants .

Use

The Maasai use the wandering ants to sew wounds. They attach the ants to the edges of the wound and the ants bite into the skin. Then the ants' bodies are severed.

literature

Individual evidence

  1. ↑ William H. Gotwald: Army ants: The biology of social predation , 1995, ISBN 0-8014-2633-2
  2. ↑ Sean G. Brady (2003): Evolution of the army ant syndrome: The origin and long-term evolutionary stasis of a complex of behavioral and reproductive adaptations . Proceedings of the National Academy of Sciences USA 100 (11): 6575-6579. doi : 10.1073 / pnas.1137809100
  3. ^ Daniel JC Kronauer (2009): Recent advances in army ant biology (Hymenoptera: Formicidae). Myrmecological News 12: 51-65.
  4. ↑ Volker Witte (2001): Organization and control of driver ants behavior in Southeast Asian ponerines of the genus Leptogenys. Diss., University of Frankfurt a. M.
  5. ↑ Mark W. Moffett (1988): Foraging Behavior in the Malayan Swarm-Raiding Ant Pheidologeton silenus (Hymenoptera: Formicidae: Myrmicinae). Annals of the Entomological Society of America, Volume 81, Number 2: pp. 356-361.

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