Polyergus
Encyclopedia
Polyergus, also called Amazon ants, is a small genus
of 6 described species (and several possible undescribed species) of "slave-raiding" ant
s. Its workers are incapable of caring for brood, in part due to their dagger-like, piercing mandibles, but more importantly, because in the evolution of their parasitism
, they have lost the "behavioral wiring" to carry out even rudimentary brood care, or even to feed themselves. Polyergus species subsist solely as a specialized brood-acquiring caste, maintaining a worker force by robbing brood of particular species in the closely related genus Formica
in massive colony-to-colony raids. The captured ants are generally referred to as "slaves" in scientific and popular literature, though recent attempts have been made to apply other human cultural models, such as describing the Polyergus individuals of a colony as "raiders" or "pirates" and the Formica workers as "helper-ants", or "domesticated animals". Biologists describe the system simply as social parsitism by Polyergus on the host Formica species.
Polyergus obtains its Formica work force by stealing pupa
e from nearby Formica colonies and carrying them back to its own nest. Back in the Polyergus nest, Formica workers are eventually helped to emerge from the cocoons by Formica workers already living there. The new workers quickly assimilate the characteristic odor of the mixed-species population of the Polyergus colony—completely without violence or coercion. The Formica workers that emerge in the mixed-species colony go on to nurse, forage, and perform other colony upkeep duties.
As far as is known, all established Polyergus colonies have only one queen. To found a new colony, a lone Polyergus queen invades a nest
of the host species, or encounters and moves in with a colony-founding queen of the host species and her first few workers. In the latter case, the host queen is allowed to survive until she has reared a number of host workers, something the Polyergus queen cannot do herself. A young Polyergus queen kills the existing Formica queen (immediately if sufficient workers are present, later if these are not yet reared) and becomes accepted by the Formica workers. These proceed to rear the first and all subsequent Polyergus brood. Clearly, this complicated and lengthy process often fails, as Polyergus colonies are relatively rare, even though each mature colony produces dozens or hundreds of new potential queens each year. To counteract the natural mortality of the Formica worker population, Polyergus workers must conduct regular raids over a 6-8 week period, every summer over the 10-15 year life span of their colony.
The raids of Amazon ants have been sensationalized as "blood baths" in popular writing. However, careful observation has demonstrated repeatedly and for all species that their brood-stealing raids are highly efficient and virtually non-violent. It is rare for even a single member of the raided Formica colony to be injured or killed. Instead, the host colony is overwhelmed, apparently by its own formic acid and alarm pheromones produced in the panic, when the marauders enter their nest en masse. Commonly, the queen and workers of the raided Formica colony evacuate and climb up nearby vegetation where they simply "wait for the problem to go away" while the Polyergus workers find and run off with their brood.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of 6 described species (and several possible undescribed species) of "slave-raiding" ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
s. Its workers are incapable of caring for brood, in part due to their dagger-like, piercing mandibles, but more importantly, because in the evolution of their parasitism
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
, they have lost the "behavioral wiring" to carry out even rudimentary brood care, or even to feed themselves. Polyergus species subsist solely as a specialized brood-acquiring caste, maintaining a worker force by robbing brood of particular species in the closely related genus Formica
Formica
Formica is a genus of ants of the family Formicidae, commonly known as wood ants, mound ants, or field ants. Formica is the type genus of the Formicidae, and of the subfamily Formicinae...
in massive colony-to-colony raids. The captured ants are generally referred to as "slaves" in scientific and popular literature, though recent attempts have been made to apply other human cultural models, such as describing the Polyergus individuals of a colony as "raiders" or "pirates" and the Formica workers as "helper-ants", or "domesticated animals". Biologists describe the system simply as social parsitism by Polyergus on the host Formica species.
Polyergus obtains its Formica work force by stealing pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
e from nearby Formica colonies and carrying them back to its own nest. Back in the Polyergus nest, Formica workers are eventually helped to emerge from the cocoons by Formica workers already living there. The new workers quickly assimilate the characteristic odor of the mixed-species population of the Polyergus colony—completely without violence or coercion. The Formica workers that emerge in the mixed-species colony go on to nurse, forage, and perform other colony upkeep duties.
As far as is known, all established Polyergus colonies have only one queen. To found a new colony, a lone Polyergus queen invades a nest
Nest
A nest is a place of refuge to hold an animal's eggs or provide a place to live or raise offspring. They are usually made of some organic material such as twigs, grass, and leaves; or may simply be a depression in the ground, or a hole in a tree, rock or building...
of the host species, or encounters and moves in with a colony-founding queen of the host species and her first few workers. In the latter case, the host queen is allowed to survive until she has reared a number of host workers, something the Polyergus queen cannot do herself. A young Polyergus queen kills the existing Formica queen (immediately if sufficient workers are present, later if these are not yet reared) and becomes accepted by the Formica workers. These proceed to rear the first and all subsequent Polyergus brood. Clearly, this complicated and lengthy process often fails, as Polyergus colonies are relatively rare, even though each mature colony produces dozens or hundreds of new potential queens each year. To counteract the natural mortality of the Formica worker population, Polyergus workers must conduct regular raids over a 6-8 week period, every summer over the 10-15 year life span of their colony.
The raids of Amazon ants have been sensationalized as "blood baths" in popular writing. However, careful observation has demonstrated repeatedly and for all species that their brood-stealing raids are highly efficient and virtually non-violent. It is rare for even a single member of the raided Formica colony to be injured or killed. Instead, the host colony is overwhelmed, apparently by its own formic acid and alarm pheromones produced in the panic, when the marauders enter their nest en masse. Commonly, the queen and workers of the raided Formica colony evacuate and climb up nearby vegetation where they simply "wait for the problem to go away" while the Polyergus workers find and run off with their brood.
External links
- http://www.antweb.org/description.do?rank=species&name=umbratus_cf&genus=polyergus&project=missouriants] - from which the text of this article is derived.
- Video of Polyergus rufescens stealing Serviformica pupae