Leaf Cutter Ants


ORDER: Hymenoptera

FAMILY: Formicidae

GENUS: Atta

SPECIES: cephalotes

DESCRIPTION:
Leaf-Cutter Ants are dark red in color. In addition to the standard ant anatomy, the back of the thorax has three pairs of teeth, or spines which help them maneuver material such as leaf fragments on their backs. Size varies by caste within each colony: the smallest are merely 2 mm wide (head size) and the largest up to 20 mm wide, with the foragers typically about 10 mm wide.

GEOGRAPHICAL RANGE AND HABITAT:
Various species of leaf-cutter ants (aka atta ants) are found in northern South America, Central America and Northern Texas. They are found in rainforest and deciduous forests as well as in open woodlands and scrub forests. Atta ants will also invade agricultural areas that supplant their forest habitats.

DIET:
Leaf-cutter ants eat a fungus which they cultivate within their nest, using masticated leaf fragments (from as many as 80 different plant species) as the nutrient substrate on which to grow fungus. The gardener-nurse ants break off chunks of fungus from the nest's interior gardens to feed other members of the colony and the larvae.

LIFE CYCLE/SOCIAL STRUCTURE:
A leaf-cutter colony is founded when a winged female ant flies out on her mating flight (revoada) which can be as far as 11 km from her natal colony. She will generally mate with 3 to 8 males during this excursion and store all the accumulated sperm from this flight for the rest of her life. After the mating flight, she will excavate a vertical shaft in the ground and create a hollowed-out chamber at the bottom of this air shaft which serves as the first room of her own nest. When the underground chamber is prepared, she rakes off her four wings, eats them, and lays her first batch of eggs. She deposits a fungus fragment from her original colony (carried in a pouch on her body) in the chamber with her eggs. Her first batch of eggs will hatch into larvae within 3-4 weeks. The fertilized eggs are destined to become the colony's first batch of female workers while any unfertilized eggs, known as trophic eggs, may be used as food. The Queen feeds these larvae on tiny shreds of fungus and supplements this diet with tropic eggs from the same clutch. Once the larvae pupate and develop into ants (40-50 days after the female laid the eggs), they immediately begin tending the fungus garden and will also take over feeding duties for the next batch of larvae and pupae for the Queen. The next two types of offspring that hatch out are a bit larger. Their jobs are either to perform ongoing nest excavation or to act as foragers. A queen can live for up to 14 years and produce more than 150 million daughters during her lifetime! At any given time, a single colony may contain 5 million or more inhabitants without any apparent conflict.

SPECIAL ADAPTATIONS:
Leaf-Cutter Ants are well adapted, by size, for the specific jobs they perform. In addition to the sole queen, there are four different "castes" of worker ants hatched in each colony. The smallest caste of ants that are hatched out first become the gardener-nurse ants who take over the tasks of tending the Queen's small fungus garden and feeding future offspring. Their fungus gardening duties include: removing any foreign matter from the nest, masticating or applying droplets of anal fluid to the cellulose substrate to speed fungal growth, and redistributing fungus spores to provide more growth opportunity within the nest. Once the gardener-nurses can sustain these duties, the Queen becomes strictly an egg-laying machine and she will begin to produce the next two castes of (1) forager-excavators and (2) within-nest specialists. The foragers are the ones generally observed in the wild on expeditions to find, cut, and haul leaf fragments. Meanwhile, the within-nest specialist ants help the gardener-nurses and perform other special functions such as cleaning, reconstructing fungus growing chambers, providing secondary processing of harvested plant material collected by the foragers, and excavating ventilation chambers to aerate the nest. Only when the colony has a thriving population and a healthy sustainable fungus supply, does the Queen produce the largest of her offspring, the soldier ants. Since soldiers must defend the nest from predators and rival colonies, they are endowed with much greater size and super-sized sharp mandibles for these defense tasks. Their larger size and energy requirements are more likely to be accommodated by a mature colony's fungus supply. Once all four working castes are in place, the Queen will produce members of the caste needed by the colony at the time.

INTERPRETIVE INFORMATION:
Leaf-cutter ants are incredibly strong and agile creatures. The foragers carry more than 6 times their own body weight while moving quickly over significant distances. A proportionate task for an average adult human would be to carry 660 pounds, while running a marathon at 4-minute-mile pace! Native peoples in the Americas used the tenacious sharp jaws of the soldier ant as sutures for holding the edges of gaping wounds together. Leaf-cutter ants are one of the most dreaded agricultural pests in the regions where they live. Once the ants determine (through cautious testing) that a particular crop is safe and suitable for advancing their fungus gardens, they are notoriously rapacious and speedy in defoliating their favored plants. Although leaf-cutters are considered pests by humans, they are important contributors in a wild ecosystem. They are prime aerators of soil and provide crucial nutrient redistribution in the forest through their discarding of spent fungus and their removal of their own waste material. The ants are also a valued source of protein for other forest animals and for humans as well. The latest scientific discovery and study regarding atta ants is that these ants make use of antibiotic chemicals to suppress the growth of parasites that threaten their fungus gardens.

OUR ANIMALS:

STATUS IN WILD:
Not endangered.

BIBLIOGRAPHY:

  1. Foster, Douglas."Small Matters" from Smithsonian Magazine, May, 2002.
  2. Holldobler, Bert & Edward Wilson. Journey to the Ants.1994.Harvard Univ. Press.
  3. Janzen, Daniel H. Costa Rican Natural History. University of Chicago Press.
  4. Schlager, Neil, Ed. Grizmek's Animal Life Encylopedia:Vol. 3. 2004. Gale Group.
  5. University of Michigan Museum of Zoology, Animal Diversity Web Site.

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