Atta texana

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Geographic Range

Fungus growing ants are found only in the new world. Atta texana is the northernmost species in the genus Atta and is found in portions of Louisiana and Texas. In Louisiana it is mainly found west of the Mississippi, primarily in the central portion of the state. In Texas this species is found in central and eastern portions of the state south to the lower Rio Grande Valley. In the Rio Grande Valley these ants are found inland and away from the mouth of the Rio Grande. This species has also been reported in Northeastern Mexico. (Drees and Merchant, 2006; Grosman, 2007; San Juan and Li, 2006a; Seymour, 2005; "Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006)

Presence of Atta texana in Louisiana may stem from human activity. Ants in the genus Atta prefer second growth forest and man-modified habitat. The clearing of the old growth pine forests in eastern Texas may have facilitated the spread of the species in previously non-colonized areas in western and central Louisiana. (San Juan and Li, 2006b)

Habitat

Atta texana colonizes roadsides, open fields, forests, and brushland. Deep sandy or loamy soils are best for ant colonies. They will preferentially setup colonies where they have access to the young foliage that they seek to harvest for the growth of their fungus. Atta texana thrives in secondary growth forest perhaps due to the more abundant understory growth found in these forests. (Drees and Merchant, 2006; San Juan and Li, 2006b; "Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006)

Physical Description

Morphologically, it is difficult to distinguish the closely related ants in the genus Atta. Differences exist in the male reproductive organs, but the species can easily be differentiated by the odor emitted from their crushed heads as the contents of their poison glands are liberated. Atta texana workers, queens, and males release the smell of mint. Nevertheless, identification in the field should not be difficult for the range of Atta texana is not known to overlap with that of other species in the genus Atta. The range of Atta mexicana is located further south and west. (Moser, et al., 1968; Weber, 1969)

Adults are rust to dark brown and larvae are cream colored. The size of the ants varies greatly depending on the caste and on the maturity of the colony. The size of the worker ants increase as the colony grows and the sources of fungus within it increase. Workers range between 3 and 12 mm. The soldiers are the largest workers, the foraging workers are medium in size, and the specialist workers are the smallest ants found in the ant colony. The queen can be as large as 18 mm while the larvae usually range between 6 to 13 mm long.

The shape of the ants varies depending on caste. Antennae of Atta texana have 11 segments and the terminal club is not well defined. Workers have 3 pairs of prominent spines on the back of the thorax and 1 pair of spines on back of head. Male reproductives have a smaller head than females. Reproductive males and females have long dark wings and are several times larger than non-reproductive workers. (Moser, 2006; "Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    3 to 18 mm
    0.12 to 0.71 in

Development

Atta texana goes through four developmental stages. Within the nest, the queen lays tiny eggs that hatch as larva. The larvae are grub like, have no eyes or legs, and eat regurgitated fungus from adult ants. After they have molted several times, the larvae spin a silky cocoon around themselves and metamorphose. This is called the pupa stage. They emerge from their cocoon as adults, and lifespan varies between castes. ("ANTS", 2007)

Reproduction

Atta texana are eusocial. On clear and moonless nights from April to June, winged males and females take flight to mate. Usually this occurs after a heavy rainfall, more than a ¼ of an inch of rain, but in areas of high rainfall this flight may take place anytime during the spring. After mating, the males die and the mated females return to the ground, lose their wings, and begin new colonies as queens. (Drees and Merchant, 2006; Grosman, 2007; "Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006)

It is not known how many times females reproduce. There is genetic evidence that some females may mate twice in their lifespan. However, males carry almost exactly the same amount of spermatozoa as the queens are able to carry in their spermatheca, suggesting that they mate only once. (Keller and Reeve, 1994)

Typically colonies have a single fertile queen which continually produces eggs (up to two million). Colonies may have up to 4 or 5 fertile queens. Most of the larvae develop into sterile female worker ants but reproductives that number in the thousands are produced annually when the colony reaches a big enough size and for as long as the fertile queen lives. In order for reproductives to leave the colony and take flight, workers ensure that the exits are wide enough and free of debris. Reproductives develop into winged fertile males and females in the spring. Prior to mating, the virgin queen takes a small portion of the fungus garden from the parent colony and stores it in her infrabuccal pocket, a hollow space and filtering device in mouths of ants. After mating the queen establishes a new colony with the fungus she conserved from the parent colony. The queens may congregate with other queens to form new colonies. (Boyd and Martin, 1975; Drees and Merchant, 2006; Grosman, 2007; "Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006; Weber, 1969)

  • Breeding interval
    Reproductive Texas leaf-cutting ants will breed once in their lifetimes.
  • Breeding season
    Reproductive Texas leaf-cutting ants breed from April to June.

During the early stages of the colony the queen takes care of her first brood of ants. This first brood becomes worker ants, which can then tend the next generation of ants. Larval ants are kept in close proximity to the fungal gardens which provide food for the developing young. As the colony grows, small nurse ants are developed to take over the task of rearing the larvae. (Drees and Merchant, 2006; Moser, 2006)

  • Parental Investment
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

There is variation in longevity within castes. The queen lives as long as the colony, which can be over a decade, but workers live one or two years. Under laboratory conditions, queens of species in the genus Atta have been shown to live over 10 years. Atta cephalotes may live to 13.0 years and Atta sexdens to 15.3 years. (Keller, 1998)

  • Typical lifespan
    Status: wild
    1 to 10+ years

Behavior

Texas leaf-cutting ant colonies have two main tasks: care for the queen and her young, and care for their cultivated fungus. These tasks require significant amounts of work, which is divided and assigned to several different castes. Thus, the organization of the ant colony is very complex. An ant colony consists of the fertile queen(s) and the workers. A high degree of task specialization amongst workers of the colony is observed and is reflected by the morphological differences between the workers. Twelve worker morphs are distinguished and grouped into three main groups, the smaller specialist workers, the medium sized workers (the foragers), and the larger workers (the soldiers). The larger workers, the soldiers, guard the entrances to the nest and patrol the foraging trails to protect the medium sized foraging ants. Occasionally the soldiers are seen foraging, but that task is primarily carried out by the foragers. The foragers also excavate the tunnels and chambers and maintain the foraging trails. The foraging trails are often well defined and stripped of most vegetation. Smaller workers receive leaf fragments at the nest and break them down into smaller pieces. Even smaller specialist ants chew and macerate the leaf fragments into a pulpy substance which they introduce the fungus on. The smaller workers which do not forage or protect the colony never leave the nest. They maintain the fungus gardens and also care for the queen and her brood.

The activity level of ants is dependent on temperature. They avoid leaving the nest on hotter days and collect leaves at night during the summer. They are noted to harvest leaves during the day especially between 45 and 80 degrees F, but not on cold, wet or cloudy days. (Boyd and Martin, 1975; Grosman, 2007; Moser, 2006; "Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006)

  • Range territory size
    4047 (high) m^2

Home Range

Colony size is dependent on the amount of resources available in the nest’s location. The area covered by a colony can be more than an acre. The ants create mounds up to 3 feet, densely clustered at the center of the nest. The fungus gardens require a relatively stable environment which is controlled by opening and closing openings to the tunnels. The fungus garden chambers can be 8 feet deep, while other extensions can be 25 feet deep and reach the water table. Lateral tunnels may be 500 feet long. (Drees and Merchant, 2006; Grosman, 2007; Moser, 2006; "Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006)

Communication and Perception

Using their sting, workers make trails with a pheromone: methyl 4-methylpyrrole-2-carboxylate. The pheromone is released from poison glands. Trails made by the poison glands of workers of larger size are more detectable then those made by workers of minor size because their sacs contain more pheromone. Mandibular glands of Atta texana contain two ketones that are both used for communication by ants: 4-methyl-3-heptanone and 2-heptanone. High concentrations repel and alarm the ants while low concentrations attract and alarm the ants. (Moser and Blum, 1963; Moser, 1964; Moser, et al., 1968)

Food Habits

Texas leaf-cutting ants feed almost exclusively on a fungus that they cultivate on the clippings of vegetation that they gather. While the workers also eat plant sap, the queen and larvae only eat the basidiomycete fungus. (Boyd and Martin, 1975)

These ants will travel long distances (up to 600 ft) to attain preferred plant species. It has been observed that they will dig tunnels under streams to get to a food source. The ants will try to harvest leaves from different plant species in order to avoid the buildup of certain chemicals in their fungus cultivars and keep them as healthy as possible. They use their powerful mandibles to cut sections of leaves off of the plant. A pile of leaf fragments accumulates around the plant which other workers carry to the nest. In only one night they are capable of defoliating an entire tree. At the nest entrance the leaves are divided into even smaller fragments and brought to the fungus gardens. Interestingly, they seem to prefer introduced species to native ones. They also prefer new growth to old and plants with higher water content. (Drees and Merchant, 2006; Moser and Blum, 1963; Moser, 2006; "Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006)

  • Plant Foods
  • sap or other plant fluids
  • Other Foods
  • fungus

Predation

The ants, especially the soldiers, have a powerful bite that they use to defend the colony against invasive predators. Also, the leaf-cutting ants use their complex tunnels and chambers to escape predation. In the rain forest, armadillos are natural predators of members of the genus Atta and local Nine-banded armadillos often feed on Texas leaf-cutting ants. (Grosman, 2007; Moser, 2006; Rao, 2000)

Ecosystem Roles

The mutualistic relationship between the ants and the basidiomycete fungus evolved between 45 and 65 million years ago and over time has resulted in an intricate relationship between the two organisms. When the medium-sized workers bring the leaf material back to the nest it is broken down into smaller segments. Smaller workers lick and masticate the leaf material and break it down into pieces as small as 1 to 2 mm. This helps remove microbes that would otherwise infect the fungus gardens and also serves to render the substrate more suitable for fungal growth. In addition, the workers add a fecal droplet to the masticated pulp that is believed to input important enzymes that facilitate the breakdown of the material by the fungus. The enzymes contained in the fecal matter are derived from the fungus consumed by the ants. This shows how strong the mutualistic relationship between the ant and the fungus is. After this processing the ants place the pulp on top of the garden and transfer fungus on the newly brought substrate. It takes about 6 weeks for the fungus to break down the material after which the consumed plant matter is removed from the nest. Substrate is continually added to the garden from the top to maintain a healthy fungus garden. The ants prune the fungus to induce growth, and optimize growing conditions by either opening or closing surface tunnels. They can thus regulate the temperature and humidity in the ant colony. Ants in the genus Atta clonally and vertically propagate this fungus. The virgin queen takes a part of the fungus grown by the parent colony and starts cultivating it into her new nest. The fungus mainly reproduces asexually and thus cultivars transmitted from generation to generation are clones of each other. (Boyd and Martin, 1975; Currie, 2001; Moser, 2006)

Female phorid flies of the species Myrmosicarius texanus and Apocephalus wallerae parasitize workers of A. texana harvesting leaves by depositing their eggs on the foragers’ heads or thoraxes using their specialized ovipositors. The flies will be more likely to deposit their eggs on the bodies of larger workers because the size of the host determines the extent of the fly larval growth. Unlike in other Atta species such as Atta colombica, minim workers of Atta texana are not known to ride on leaves carried by foraging workers to thwart off parasitizing attempts by phorid flies. (Waller and Moser, 1990)

The inquiline roach Attaphila fungicola is often found associated with the fungus gardens of most Atta texana nests. The roaches disperse by attaching their bodies to virgin queens as they take on their mating flights. They successfully disperse to new ant colonies in this manner. (Moser, 1964)

Mutualist Species
  • basidiomycete fungus
Commensal/Parasitic Species

Economic Importance for Humans: Positive

This species is not known to have any economic importance to humans.

Economic Importance for Humans: Negative

Atta texana is considered a major pest in Texas and Louisiana. The foraging activities of the ant damage crops and prevent the reforestation of southern yellow pines. It is estimated that Atta texana is responsible for United States $5 million in annual agricultural losses. Atta texana is also known to damage landscape plants and gardens. Young pine seedlings are destroyed in a matter of days but will not be attacked once they reach a height two to three feet. The ants defoliate pine trees usually when other green plants are scarce such as during the winter. Damage done by the leaf-cutting ants resembles damage carried out by cutting bees and sawflies. The pest has been occasionally sited in homes carrying food material such as cereal, but this is only a minor occurrence and problem. ("Texas Leaf Cutting Ant, Atta texana (Buckley)", 2006; "TEXAS LEAFCUTTING ANT,", 2007)

  • Negative Impacts
  • injures humans
    • bites or stings
  • crop pest

Conservation Status

These ants are in no need of conservation as they are plentiful in numbers and considered to be a pest by some.

Contributors

Alexandre Chausson (author), Rutgers University, David V. Howe (editor), Rutgers University, Rachelle Sterling (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

crepuscular

active at dawn and dusk

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

eusocial

the condition in which individuals in a group display each of the following three traits: cooperative care of young; some individuals in the group give up reproduction and specialize in care of young; overlap of at least two generations of life stages capable of contributing to colony labor

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

internal fertilization

fertilization takes place within the female's body

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

mycophage

an animal that mainly eats fungus

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parthenogenic

development takes place in an unfertilized egg

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

soil aeration

digs and breaks up soil so air and water can get in

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

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USDA Forest Service - Forest Health Protection, Southern Region. 2007. "TEXAS LEAFCUTTING ANT," (On-line). Atta Texana. Accessed November 10, 2007 at http://www.fs.fed.us/r8/foresthealth/idotis/insects/txlfcut.html.

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Moser, J., R. Brownlee, R. Silverstein. 1968. Alarm pheromones of the ant Atta texana. Journal of Insect Physiology, Volume 36 issue 3: 14, 4, 529-530.

Moser, J. 1964. Inquiline Roach Responds to Trail-Marking Substance of Leaf-Cutting Ants. Science, 143: 1048-1049.

Moser, J., M. Blum. 1963. Trail marking substance of the Texas Leaf-Cutting Ant. Science, 140: 1228.

Moser, J. 2006. "Town Ants" (On-line). Atta Texana. Accessed November 10, 2007 at http://www.srs.fs.usda.gov/4501/townants.htm.

Rao, M. 2000. Variation in leaf-cutter ant (Atta sp.) densities in forest isolates: the potential role of predation. Journal of Tropical Ecology, 16/2: 209-225.

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San Juan, A., H. Li. 2006. "Did the Texas Bonanza Era in 1876-1930 facilite the spread of Atta texana into Louisiana?" (On-line). A. San Juan's: The Lurker's Guide to Leaf Cutter Ants. Accessed November 10, 2007 at http://www.blueboard.com/nfu/spread.htm.

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Waller, D., J. Moser. 1990. Invertebrate enemies and nest associates of the leaf-cutting ant Atta texana (Buckley) (Formicudae, Attini). Pp. 256-273 in R Vander Meer, K Jaffe, A Cedeno, eds. Applied Myrmecology: A World Perspective. Boulder, San Francisco, and Oxford: Westview Press. Accessed November 20, 2007 at http://www.srs.fs.usda.gov/pubs/ja/ja_waller001.pdf.

Weber, . 1969. Ecological relations of three Atta species in Panama. Ecology, 50: 141-147.