Army ant
Parts of this article (those related to the previous dorylomorph subfamilies (Dorylinae, Aenictinae, Aenictogitoninae, Ecitoninae and Leptanilloidinae), all of which now are synonyms of Dorylinae) need to be updated.(September 2014) |
The name army ant (or legionary ant or marabunta[1]) is applied to over 200 ant species in different lineages. Because of their aggressive predatory foraging groups, known as "raids", a huge number of ants forage simultaneously over a limited area.[2]
Another shared feature is that, unlike most ant species, army ants do not construct permanent nests; an army ant colony moves almost incessantly over the time it exists. All species are members of the true ant family,
Most
Originally, some of the Old World and New World lineages of army ants were thought to have evolved independently, in an example of convergent evolution. In 2003, though, genetic analysis of various species suggests that several of these groups evolved from a single common ancestor, which lived approximately 100 million years ago at the time of the separation of the continents of Africa and South America, while other army ant lineages (Leptanillinae, plus members of Ponerinae, Amblyoponinae, and Myrmicinae) are still considered to represent independent evolutionary events.[3] Army ant taxonomy remains in flux, and genetic analysis will likely continue to provide more information about the relatedness of the various taxa.[4]
Morphology
Workers
The workers of army ants are usually blind or can have compound eyes that are reduced to a single lens. There are species of army ants where the worker caste may show polymorphism based on physical differences and job allocations; however, there are also species that show no polymorphism at all.[5] The worker caste is usually composed of sterile female worker ants.[6]
Soldiers
The soldiers of army ants are larger than the workers, and they have much larger mandibles than the worker class of ants, with older soldiers possessing larger heads and stronger mandibles than the younger ones. They protect the colony, and help carry the heaviest loads of prey to the colony bivouac.
Males
Males are large in size and have a large cylindrical abdomen, highly modified mandibles and uncommon genitalia not seen in other ants.[7] They have 13 segments on their antennae, are alated (have wings) and therefore can resemble wasps.[5] Males are born as part of a sexual brood.[7] As soon as they are born, they will fly off in search of a queen to mate with. In some instances where males seek to mate with a queen from an existing colony, the receiving workers will forcibly remove the wings in order to accommodate the large males into the colony for mating.[8] Because of their size, males are sometimes called "sausage flies" or "sausage ants."[9]
Queen
Colonies of real army ants always have only one queen, while some other ant species can have several queens. The queen is dichthadiigyne (a blind ant with large gaster) but may sometimes possess vestigial eyes.[5] The queens of army ants are unique in that they do not have wings, have an enlarged gaster size and an extended cylindrical abdomen.[8] They are significantly larger than worker army ants and possess 10–12 segments on their antennae.[5] Queens will mate with multiple males and because of their enlarged gaster, can produce 3 to 4 million eggs a month, resulting in synchronized brood cycles and colonies composed of millions of individuals all related to a single queen.[5][10]
Behaviour
Army ant syndrome
The term "army ant syndrome" refers to
Most ant species will send individual scouts to find food sources and later recruit others from the colony to help; however, army ants dispatch a cooperative, leaderless group of foragers to detect and overwhelm the prey at once.[3][5] Army ants do not have a permanent nest but instead form many bivouacs as they travel. The constant traveling is due to the need to hunt large amounts of prey to feed its enormous colony population.[5] Their queens are wingless and have abdomens that expand significantly during egg production.[8] This allows for the production of 3–4 million eggs every month and often results in synchronized brood cycles, thus each colony will be formed of millions of individuals that descend from a single queen. These three traits are found in all army ant species and are the defining traits of army ants.[3][11]
Nomadic and stationary phase
Army ants have two phases of activity – a nomadic (wandering) phase and a stationary (statary) phase – that constantly cycle, and can be found throughout all army ant species.[8]
The nomadic phase begins around 10 days after the queen lays her eggs. This phase will last approximately 15 days to let the larvae develop. The ants move during the day, capturing
The stationary phase, which lasts about two to three weeks, begins when the
Colony fission
Army ants will split into groups when the size of the colony has reached a size threshold, which happens approximately every three years.[13] Wingless virgin queens will hatch among a male sexual brood that hatches at a later date. When the colony fissions, there are two ways new queens are decided. A possible outcome is a new queen will stay at the original nest with a portion of the workers and the male brood while the old queen will leave with the rest of the workers and find a new nest. Another possibility is that the workers will reject the old queen and new queens will each head a newly-divided colony.[2][8] The workers will affiliate with individual queens based on the pheromone cues that are unique to each queen. When new bivouacs are formed, communication between the original colony and the new bivouacs will cease.[8]
Queen behaviour
Being the largest ants on Earth, army ants, such as African
When the queen ant dies, there is no replacement and army ants cannot rear emergency queens. Most of the time, if the queen dies, the colony will likely die too. Queen loss can occur due to accidents during emigrations, predator attack, old age or illness.[13] However, there are possibilities to avoid colony death. When a colony loses its queen, the worker ants will usually fuse with another colony that has a queen, within a few days.[6][15] Sometimes, the workers will backtrack along the paths of prior emigrations to search for a queen that has been lost or merge with a sister colony.[15][16] By merging with a related colony, the workers would increase their overall inclusive fitness.[13] The workers that merge into a new colony may cause the colony to increase in size by 50%.
Sexual selection by workers
Workers in army ant species have a unique role in selecting both the queen and the male mate.
When the queens emerge, the workers in the colony will form two 'systems' or arms in opposite directions. These queens that are hatched will move down either of the arms and only two queens will succeed, one for each branch. Any remaining new queens will be left in the middle and are abandoned. Two new bivouacs will be formed and break off into different directions. The workers will surround the two to-be queens to ensure they survive. These workers that surround the queens are affected by the CHC (pheromone) profile emitted by the new queen.[8]
When males hatch from their brood, they will fly off to find a mate. For males to access the queen and mate, they must run through the workers in the colony. Males that are favoured are superficially similar in size and shape to the queen. The males also produce large quantities of pheromones to pacify the worker ants.[8]
Reproduction responsibilities and problems
In a
Ant mills
Army ants can get lost from the pheromone track while foraging, making the ants follow each other in a circular motion, potentially causing them to die of exhaustion.[18]
Foraging
The whole colony of army ants can consume up to 500,000 prey animals each day, so can have a significant influence on the
When army ants forage, the trails that are formed can be over 20 m (66 ft) wide and over 100 m (330 ft) long.[20] They stay on the path through the use of a concentration gradient of pheromones. The concentration of pheromone is highest in the middle of the trail, splitting the trail into two distinct regions: an area with high concentration and two areas with low concentrations of pheromones. The outbound ants will occupy the outer two lanes and the returning ants will occupy the central lane.[20] The returning worker ants have also been found to emit more pheromones than those leaving the nest, causing the difference in concentration of pheromone in the trails.[21] The pheromones will allow foraging to be much more efficient by allowing the army ants to avoid their own former paths and those of their conspecifics.[19] Scaffolds structure has been observed when workers carried heavy prey food to inclined surface. Walking ants are prevented from falling by other ants.[22]
While foraging, army ants cause many invertebrates to flee from their hiding places under leaves of the forest floor, under tree bark, and other such locations, thereby allowing predators to catch them more easily. For example, in the tropical rainforests of Panama, swarms of army ants attract many species of birds to this feast of scrambling insects, spiders, scorpions, worms, and other animals. Some of these birds are named "antbirds" due to this tendency.
Nesting
Army ants do not build a nest like most other ants. Instead, they build a living nest with their bodies, known as a
Symbionts
Many species of army ants are widely considered to be
It has been speculated that the nocturnal foraging of some army ant species is done to reduce kleptoparasitism by birds, since the bird kleptoparasites of army ants are diurnal.[12]
Taxonomy
Historically, "army ant" in the broad sense referred to various members of five different ant subfamilies. In two of these cases, the
A 2003 study of thirty species (by Sean Brady of
Accordingly, the "army ants" as presently recognized consist of legionary species in these genera:
- Subfamily Dorylinae (Aenictinae, Aenictogitoninae, Cerapachyinae, Ecitoninae and Leptanilloidinae, 2014)[41]
- Aenictus
- Asphinctanilloides
- Cheliomyrmex
- Dorylus
- Eciton
- Labidus
- Leptanilloides
- Neivamyrmex
- Nomamyrmex
- Subfamily Leptanillinae
- Subfamily Myrmicinae
- Pheidologeton
- Subfamily Ponerinae
- Leptogenys (some species)
- Simopelta
- Subfamily Amblyoponinae
See also
- "Carl Stephensonabout soldier ants swarming over a Brazilian plantation
Notes
- ^ "There are also interesting [evolutionary] convergences within the ants. Although most ant colonies live a settled existence in a fixed nest, there seems to be a successful living to be made by wandering in enormous pillaging armies. This is called the legionary habit." (Dawkins 1986)
- ^ "Because army ants are found almost everywhere, scientists postulated that they evolved many times after the break-up and dispersal of the supercontinent Gondwana just over 100 million years ago. The conventional view of the evolution of army ants needs a revision because of new data obtained by Sean Brady, a Cornell University, US, entomologist who has discovered that these ants evolved from a common ancestor."(Whitehouse 2003)[39]
References
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- ^ OCLC 210501.
- ^ PMID 12750466.
- ^ "Army Ants Harbor a Host-Specific Clade of Entomoplasmatales Bacteria". ResearchGate. Retrieved 2019-04-04.
- ^ ISBN 9780323152167. in Hermann 1982
- ^ OCLC 32087436.
- ^ OCLC 468279677.
- ^ .
- ^ "Driver Ants – info and games". www.sheppardsoftware.com. Retrieved 2019-04-04.
- ^ S2CID 13887869.
- PMID 16157878.
- ^ ISSN 0307-6946.
- ^ a b c Kronauer, Daniel J. C. (2009). "Recent advances in army ant biology (Hymenoptera: Formicidae)". Myrmecological News. 12: 51–65.
- ^ S2CID 36371272.
- ^ PMID 19889701.
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- ^ Reid, Chris; Carlesso, Daniele (April 19, 2021). "Bridges, highways, scaffolds: how the amazing engineering of army ants can make us smarter creators". The Conversation. Retrieved 2021-04-20.
- ^ Angehr G, Dean R. 2010. The birds of Panama: a field guide. Cornell Univ. Press, Ithaca, New York. 456 pp.[ISBN missing][page needed]
- ^ Kent Livezey, Birding Pipeline Panama, Panama City, Panama[ISBN missing][page needed]
- ISBN 978-0-393-31570-7.
- ^ "The Army Ant". Kaieteur News. 2013-08-11. Retrieved 2019-04-04.
- .
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- ^ S2CID 32688600.
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{{cite book}}
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- ^ Whitehouse, David (2003-05-10). "Ant history revealed". Science & Environment. BBC News Online. Retrieved 2009-01-14.
- S2CID 84043939.
- PMID 24886136.
Bibliography
- Hermann, Henry R., ed. (1982). Social Insects. Vol. IV. New York: OCLC 37854847.