Difference between revisions of "Army ant" - New World Encyclopedia

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Known as "driver ants" or "safari ants," members of the genus ''Dorylus'' are found primarily in central and east [[Africa]], though the range extends to tropical [[Asia]]. There are some 70 species presently recognized, though another 60 names are applied at the rank of subspecies. Unlike the [[New World]] members of the [[Ecitoninae]], they do form [[anthill]]s, although these are temporary (a few days up to three months). Each [[colony]] can contain over 20 million individuals. As in their New World counterparts, there is a [[soldier]] class among the workers, which is larger, with a very large head and pincer-like [[mandible]]s. They are capable of [[sting (biology)|stinging]], but very rarely do so, relying instead on their powerful shearing jaws. All ''Dorylus'' species are blind, though they, like most varieties of ants, communicate primarily through [[pheromone]]s.
 
Known as "driver ants" or "safari ants," members of the genus ''Dorylus'' are found primarily in central and east [[Africa]], though the range extends to tropical [[Asia]]. There are some 70 species presently recognized, though another 60 names are applied at the rank of subspecies. Unlike the [[New World]] members of the [[Ecitoninae]], they do form [[anthill]]s, although these are temporary (a few days up to three months). Each [[colony]] can contain over 20 million individuals. As in their New World counterparts, there is a [[soldier]] class among the workers, which is larger, with a very large head and pincer-like [[mandible]]s. They are capable of [[sting (biology)|stinging]], but very rarely do so, relying instead on their powerful shearing jaws. All ''Dorylus'' species are blind, though they, like most varieties of ants, communicate primarily through [[pheromone]]s.
  
Seasonally, when [[food]] supplies become short, they leave the hill and form marching columns of 20,000,000 ants which are considered a menace to people, though they can be easily avoided; a column can only travel about 20 meters in an hour. It is for those unable to move, or when the columns pass through homes, that there is the greatest risk. There have been reported cases of people&mdas;usually the young, infirm, or otherwise debilitated who could not escape— being killed and eventually consumed by them, often dying of [[asphyxiation]]. Their presence is, conversely, beneficial to certain human communities, such as the [[Maasai]], as they perform a pest prevention service in farming communities, consuming the majority of other crop-pests, from [[insect]]s to large [[rat]]s. A large part of their diet is earthworms.
+
Seasonally, when [[food]] supplies become short, they leave the hill and form marching columns of 20 million ants, which are considered a menace to people, though they can be easily avoided; a column can only travel about 20 meters in an hour. It is for those unable to move, or when the columns pass through homes, that there is the greatest risk. There have been reported cases of people&mdas;usually the young, infirm, or otherwise debilitated who could not escape— being killed and eventually consumed by them, often dying of [[asphyxiation]]. Their presence is, conversely, beneficial to certain human communities, such as the [[Maasai]], as they perform a pest prevention service in farming communities, consuming the majority of other crop-pests, from [[insect]]s to large [[rat]]s. A large part of their diet is earthworms.
  
 
The bite of the large soldier ants is severely painful, each soldier leaving two puncture wounds when removed. Removal is difficult, however, as their jaws are extremely strong, and one can pull a soldier ant in two without it releasing its hold. Such is the strength of the ant's jaws, in East Africa they are used as natural, emergency [[suture]]s. [[Maasai]] moroni, when they suffer a gash in the bush, will use the soldiers to stitch the wound, by getting the ants to bite on both sides of the gash, then breaking off the body. This seal can hold for days at a time.
 
The bite of the large soldier ants is severely painful, each soldier leaving two puncture wounds when removed. Removal is difficult, however, as their jaws are extremely strong, and one can pull a soldier ant in two without it releasing its hold. Such is the strength of the ant's jaws, in East Africa they are used as natural, emergency [[suture]]s. [[Maasai]] moroni, when they suffer a gash in the bush, will use the soldiers to stitch the wound, by getting the ants to bite on both sides of the gash, then breaking off the body. This seal can hold for days at a time.

Revision as of 17:37, 8 September 2007

African Dorylus raid

Army ant (or legionary ant) is the common name for the members of more than 200 known ant species, in different lineages, characterized primarily by their aggressive predatory foraging groups, known as "raids", in which huge numbers of ants (swarms) all forage simultaneously over a certain area, attacking prey en masse. They also share the habit of not constructing a permanent nest, unlike most ants, and an army ant colony moves almost incessantly over the time it exists.

Army ants do not represent a formal taxonomic rank and are scattered over 18 genera in 5 or 6 subfamilies (depending on the taxonomic scheme). All species are members of the true ant family Formicidae, but there are several groups that have independently evolved the same basic behavioral and ecological syndrome. This syndrome is often referred to as "legionary behavior", and is an example of convergent evolution. Most New World army ants belong to the subfamily Ecitoninae. Eciton burchellii, whose common name is "army ant," is considered to be the archetypal species.

Genera and species

Historically, "army ant" referred, in the broad sense, to various members of 5 different ant subfamilies: Ponerinae, Myrmicinae, Dorylinae, Leptanillinae, and Ecitoninae. In two of these cases, the Ponerinae and Myrmicinae, it is only a few species and genera that exhibit legionary behavior. In the other three lineages, Ecitoninae, Dorylinae, and Leptanillinae, all of the constituent species are legionary. More recently, ant classifications now recognize an additional New World subfamily, Leptanilloidinae, which also consists of obligate legionary species, and thus is another group now included among the army ants.

A 2003 study of thirty species indicates that the ecitonine and doryline army ants together formed a monophyletic group: all shared identical genetic markers that suggest a common ancestor. Brady concluded that these two groups are therefore a single lineage that evolved in the mid-Cretaceous period in Gondwana (Whitehouse 2003), and so the two subfamilies are now generally united into a single subfamily Ecitoninae, though this is not universally recognized (Engel 2005).

Accordingly to the taxonomic scheme whereby Ecitoninae includes genera previously classified in Dorylinae, the following genera of army ants are recognized:

Subfamily Ponerinae:

  • Leptogenys (some species)
  • Onychomyrmex
  • Simopelta

Subfamily Myrmicinae:

  • Pheidolegeton

Subfamily Leptanilloidinae:

  • Asphinctanilloides
  • Leptanilloides

Subfamily Leptanillinae:

  • Anomalomyrma
  • Leptanilla
  • Phaulomyrma
  • Protanilla
  • Yavnella

Subfamily Ecitoninae:

  • Aenictus
  • Cheliomyrmex
  • Dorylus
  • Eciton
  • Labidus
  • Neivamyrmex
  • Nomamyrmex

Army ant taxonomy remains ever-changing, and genetic analysis will continue to provide more information about the relatedness of the various species. Many genera contain large numbers of taxa at the rank of subspecies (e.g., Dorylus, in which some 60 of roughly 130 named taxa are only considered subspecies at present).

Ecitoninae

Ecitoninae
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Hexapoda
Class: Insecta
Order: Hymenoptera
Suborder: Apocrita
Superfamily: Vespoidea
Family: Formicidae
Subfamily: Ecitoninae
Tribes

New World tribes:

  • Cheliomyrmecini
  • Ecitonini

Old World tribes:

  • Dorylini
  • Aenictini (often included in Dorylini)

Most New World army ants belong to the subfamily Ecitoninae.

This subfamily is further broken into two groups in the New World, the tribes Cheliomyrmecini and Ecitonini. The former contains only the genus Cheliomyrmex, and the tribe Ecitonini contains four genera, Neivamyrmex, Nomamyrmex, Labidus, and Eciton, the genus after which the group is named (Brady 2003). The genus Neivamyrmex is the largest of all army ant genera, containing some 120 species, all in the United States. The most predominant species of Eciton is Eciton burchellii, whose common name is "army ant" and which is considered to be the archetypal species.

The Old World army ants within Ecitoniane are divided between the two tribes Aenictini and Dorylini, each of which is made up of a single genus. In the former case it is Aenictus, which contains over 100 species of army ant, while the Dorylini contains the aggressive "driver ants" in the genus Dorylus, of which there are some 70 species known. Often, taxonomic schemes include Aenictini within Dorylini, giving just one Old World tribe.

New World army ants

A representative individual from the soldier caste of the New World army ant species Eciton burchelli with characteristically shaped mandibles.

There are about 150 species of army ants in the New World (that is, North, South, and Central America). Although these army ant species are found from Kansas to Argentina, few people in North America realize that there are plenty of army ants living in the United States, in part because the colonies are rarely very abundant, and because the United States species (mostly genus Neivamyrmex) are quite small (~5 mm), with small and generally unobtrusive raiding columns, most often active at night, and easily overlooked.

Eciton burchellii and Eciton hamatum are the most visible and best studied of the New World army ants because they forage above ground and during the day, in enormous raiding swarms. Their range stretches from southern Mexico to the northern part of South America.

Old World army ants

There are over 100 species of army ants in the Old World, with approximately equal numbers in the genera Aenictus and Dorylus. The latter group is by far the better-known.

Known as "driver ants" or "safari ants," members of the genus Dorylus are found primarily in central and east Africa, though the range extends to tropical Asia. There are some 70 species presently recognized, though another 60 names are applied at the rank of subspecies. Unlike the New World members of the Ecitoninae, they do form anthills, although these are temporary (a few days up to three months). Each colony can contain over 20 million individuals. As in their New World counterparts, there is a soldier class among the workers, which is larger, with a very large head and pincer-like mandibles. They are capable of stinging, but very rarely do so, relying instead on their powerful shearing jaws. All Dorylus species are blind, though they, like most varieties of ants, communicate primarily through pheromones.

Seasonally, when food supplies become short, they leave the hill and form marching columns of 20 million ants, which are considered a menace to people, though they can be easily avoided; a column can only travel about 20 meters in an hour. It is for those unable to move, or when the columns pass through homes, that there is the greatest risk. There have been reported cases of people&mdas;usually the young, infirm, or otherwise debilitated who could not escape— being killed and eventually consumed by them, often dying of asphyxiation. Their presence is, conversely, beneficial to certain human communities, such as the Maasai, as they perform a pest prevention service in farming communities, consuming the majority of other crop-pests, from insects to large rats. A large part of their diet is earthworms.

The bite of the large soldier ants is severely painful, each soldier leaving two puncture wounds when removed. Removal is difficult, however, as their jaws are extremely strong, and one can pull a soldier ant in two without it releasing its hold. Such is the strength of the ant's jaws, in East Africa they are used as natural, emergency sutures. Maasai moroni, when they suffer a gash in the bush, will use the soldiers to stitch the wound, by getting the ants to bite on both sides of the gash, then breaking off the body. This seal can hold for days at a time.

References
ISBN links support NWE through referral fees

  • Brady, S. 2003. Evolution of the army ant syndrome: The origin and long-term evolutionary stasis of a complex of behavioral and reproductive adaptations. PNAS 100(11): 6575-6579.
  • Engel, M. S., and D. A. Grimaldi. 2005. Primitive new ants in Cretaceous amber from Myanmar, New Jersey, and Canada (Hymenoptera: Formicidae). American Museum Novitates 3485: 1–24.
  • Gotwald, W. H. 1995. Army Ants: The Biology of Social Predation. Ithaca, New York: Cornell University Press. ISBN 0801499321.
  • Hölldobler, B., and E. O. Wilson. 1990. The Ants. Cambridge, Mass: Belknap Press of Harvard University Press. ISBN 0674040759.
  • O'Donnell, S., M. Kasparim, and J. Lattke. 2005. [Extraordinary predation by the neotropical army ant Cheliomyrmex andicola: Implications for the evolution of the army ant syndrome. Biotropica 37: 706-709.
  • Rice, N. H., and A. M. Hutson. 2003. Antbirds and army-ant swarms. In C. Perrins, ed., Firefly Encyclopedia of Birds. Firefly Books. ISBN 1552977773.
  • Whitehouse, D. 2003. Ant history revealed. BBC News May 10, 2003. Retrieved September 8, 2007.

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