Leaf cutter ant

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Atta cephalotes , Wilhelma , Stuttgart

As leaf-cutting ants refers to various ant species , the part with their mouthparts plant leaves into small pieces, which they carry in their construction. Leaf cutter ants that specialize in grass are also called grass cutter ants . The more than 40 known species of leaf cutter ants come from the two genera Atta and Acromyrmex . Their distribution area includes the tropics and subtropics of America, extends from Louisiana or Texas in the north to Patagonia in the south of Argentina .

The natural scientist Thomas Belt was the first to recognize in 1874 what the ants use these leaves for: They do not eat the leaves themselves, but chew them up and use them as a substrate to grow a special mushroom from the genus of the Egerling umbrella ( Leucoagaricus ) on which they feed.

The mushroom gardens

The ants set up real mushroom farms , which they constantly expand and maintain. The mushrooms are grown on a finely tuned assembly line column in which each of the 29 different steps is carried out by a special caste of animals. A leaf laid down by a harvest worker on the construction site is picked up by a smaller worker and cut into pieces about a millimeter in diameter. These are taken over by even smaller workers, chewed, formed into small spheres and added to a pile of similar material.

This pile of material, the substrate, forms a kind of garden and is criss-crossed by tunnels, so that its structure resembles a bath sponge . The fungus growing on it spreads like bread mold on the plant matter.

Queen of the species Atta colombica with brood and workers on mushroom substrate
Workers of the species Atta colombica cut up the entire foliage of a young tree

The mushroom gardens are controlled by the smallest workers: They feel the surface of the fungal network and clean it of spores and fungal threads of foreign molds . They repeatedly pluck out a piece of the fungal lawn and bring it to their conspecifics as food or they put fungal threads on fresh plant material and thus start new cultures. They also regularly bite off the ends of the fungal threads, preventing the formation of fruiting bodies. Instead, protein-containing, bulbous thickenings develop, which are called gongylidia .

The symbiosis between the ants and the fungus is so close that both could no longer exist without each other. Because the fungus itself can be attacked by a hose fungus that destroys it. Research suggests that the ants carry bacteria on their bodies that not only inhibit the growth of the tubular fungus, but also fertilize their fodder fungus.

Size and structure of a nest

A leaf cutter ant queen can give birth to up to 150 million workers, of which two to three million are alive at any one time. A nest is ramified and contains not only chambers for the mushroom gardens, but also rubbish chambers in which dead ants, leached leaves and dead mushrooms are disposed of.

A nest created in Brazil by the species Atta , later poured with plaster and finally excavated, contained over a thousand different sized chambers, 390 of which were filled with mushroom gardens and ants. The building covered an area of ​​50 square meters and was eight meters deep.

Harm and benefit

The ants can cause a lot of damage in plantations of crops such as citrus plants , grain , cabbage plants , vines , fruit , cocoa , cotton , coconut palms and many others, because a colony can cut as much vegetation per day as an adult cow eats.

Some species of the Atta ant species use the grasslands in Brazil , Uruguay and Argentina to harvest plant material. These grass cutter ants include Atta bisphaerica , Atta capiguara , Atta laevigata and Atta vollweideri . It has been shown that herds of cattle avoid those parts of the pastures that are populated by the grass-cutting ants. These ants are endowed with well-developed thorns on their backs. It is believed that this protective mechanism is sufficient to keep the cattle away from the pastures around the ant colonies.

Since the ants move large amounts of soil when expanding their nest, they not only aerate the soil, but also circulate nutrients that are important for other organisms. The work of leaf cutter ants can make jungle soil ten times more fertile.

Enemies

The natural enemies of the leaf cutter ants are anteaters , armadillos , lizards and birds . In addition, humans try to fight them in many places with chemical means.

Ants of the genus Azteca , which live in the hollow branches of certain plants, are among the opponents of the leaf cutter ants . B. in those of ant trees ( Cecropia ), and from these plants are also supplied with food. In return, they defend these plants against predators, especially leaf cutter ants. The Azteca ants build cardboard corridors along the branches with holes into which the leaf cutter ants step. In these cardboard tubes, protected from the much larger leaf cutter ants, the Azteca ants fix the leaf cutter ants entering the holes with their mandibles . When trying to break free, the leaf cutter ants step into further traps until they can no longer move at all. So they can be killed in the end without great danger.

The entomologist Meinhard Jacoby received a patent in 1931 for a means to eradicate leaf-cutting ants.

Others

In some regions, leaf cutter ants are used by the local population to heal wounds. The mandibles of the large soldiers (a special caste within the ants) are placed on the wound edges in such a way that they close when they bite. After the animal's body has been severed, the mandibles remain closed for a few days.

In Mexico and Colombia , leaf cutter ants are eaten as a culinary specialty, hormiga culona .

In many zoos, leaf cutter ants are used as show insects because these animals grow up very quickly, are active all year round and the transport of leaves can be easily observed.

Field workers

The team of field workers includes scouts who look for suitable shrubs and trees in the area.

They create a scent trail on which the leaf cutters migrate from the underground nest to their place of use. There they cut pieces of leaf out of the foliage with their razor-sharp pliers.

Transporters drag the leaf pieces back to the nest like sails, but dangers such as B. Humpback flies (Phoridae spp.). These attack the ants with their leaves from the air, because then they are defenseless. Therefore, mostly short bodyguards ride on the leaf fragments and defend the transporters against attacks from the air.

In field experiments with the species Atta colombica named after Christopher Columbus , indications were found that the animals of this species have a magnetic sense.

Systematics

The species of leafcutter ants belong within the family of ants (Formicidae) for the subfamily of the node ants (Myrmicinae) and the tribes of Attini . They are divided into the genera Atta and Acromyrmex .

Species from the genus Atta :

Species from the genus Acromyrmex :

Individual evidence

  1. ^ A b Harold G. Fowler, Norma Bianca Saes: Dependence of the activity of grazing cattle on foraging grass-cutting ants (Atta spp.) In the southern Neotropics. In: Journal of Applied Entomology 101, 1-5, pp. 154-158, 1986
  2. ↑ Thalles C. Mattoso et al .: Symbiotic bacteria on the cuticle of the leaf-cutting ant Acromyrmex subterraneus subterraneus protect workers from attack by entomopathogenic fungi. In: Biology Letters. 8, 2012, p. 461, doi : 10.1098 / rsbl.2011.0963 .
  3. ↑ Youtube video
  4. ^ Database of the German Patent and Trademark Office .
  5. ↑ Zoo Berlin : An unusual partnership - the leaf cutter ants and their mushrooms. ( Memento of March 8, 2008 in the Internet Archive )
  6. ↑ AJ Riveros and RB Srygley: Do leafcutter ants, Atta colombica, orient Their path-integrated vector home with a magnetic compass? In: Animal Behavior. Volume 75, No. 4, 2008, pp. 1273-1281, doi: 10.1016 / j.anbehav.2007.09.030 .
  7. ^ Atta Fabricius, 1804 in the ITIS Report
  8. ^ Acromyrmex Mayr, 1865 in the ITIS Report

literature

  • Wolfgang Hachtel: Bacteria protect the fungal gardens of leaf cutter ants , in: Spectrum of Science No. 9, 1999, pp. 14-17
  • Bert Hölldobler , Edward O. Wilson : Ants. The discovery of a fascinating world , Piper, Munich 2001, ISBN 3-492-23414-3
  • Bert Hölldobler , Edward O. Wilson : Leaf cutter ants - the perfect superorganism , Springer, Berlin, Heidelberg 2011, ISBN 978-3-642-16705-8
  • Katja Ueberschaer, Christian Ziegler: Leaf cutter ants. The triumph of the collective , in: GEO Wissen No. 25 (Rainforest), Gruner & Jahr, Hamburg 1999, pp. 30–39

Web links

Commons : Leaf cutter ants  - Collection of images, videos, and audio files