You wouldn't think that a little ant would or could be very interesting. Well, in this case I HAVE to disagree and if you will follow along here for a few minutes, I think YOU too will think so. Leafcutter ants represent the pinnacle of social and technological expression in ants. Not only are they the only animals (other than humans) that cultivate their own food from fresh vegetation, but they also use sophisticated antibiotics against fungal pests in their gardens!

Chemical Secretions of the leaf-cutter ant Acromyrex octospinosus

As you might expect, many leaf-cutting ants cut the leaves of trees. Leaf-cutters will change the type of leaves they get at any one time depending on the ph chemistry in their nests. Workers of different size do different jobs. While the larger workers cut the leaf, the smaller workers guard them against attack by flies. As in all ants, the workers are all female.

When the larger worker finishes cutting a leaf fragment, smaller workers climb onto the leaf fragment to guard the larger worker. Leaf-cutting ants can carry loads weighing up to twelve times their own weight. Usually, they carry loads only two to four times their own weight. Leaf-cutters often cut leaves fifty to one hundred meters away from their nest. Each round-trip to a tree may take an ant several hours.

The nests are built below ground, sometimes extending over an area of 200 square meters, with galleries to a depth of six meters. The largest nests provide homes for single colonies of up to five million insects. Trails span out from the nests, often for 100 meters or more. Inside the nest, the ants do not eat the leaf fragments. Instead, smaller workers cut the leaves into small pieces which they use as fertilizer for growing a fungus that they use for food. When a certain protien is needed in the fungus, they chew a certain type of leaf up to form a compost on which they cultivate this nutritional breadlike fungus whose tiny white fruiting bodies provide them with food. So evolved has this symbiosis become that the fungus has lost its reproductive ability (it no longer produces sexual spores) and relies exclusively on the ants for propagation.

Each colony of Atta cephalotes has one mother queen who can live more than fifteen years and grow up to 5 centimeters long. All the workers are her daughters. When the hatchlings mature enough to divide the garden, each potential queen takes a piece of the spore as a culture to begin the new gardens food supply. The species has evolved different physical castes, each specializing in its own social tasks. The cutting and carrying are performed by intermediate-size workers ("medias"), guarded by ferocious-looking "majors," or soldier ants, about two centimeters long and with disproportionately large heads and jaws that they use to protect the workers -- usually fighting to the death -- from even the largest marauder. They also work to keep the trails clear. Most of the workers are tiny minors ("minimas"), which tend the nest and mulch it to feed the fungus gardens. Even small "minimas" ride atop the leaves carried by their larger siblings to guard against parasitic phorid flies that attempt to lay their eggs on the leaves so that the eggs may be taken underground, where they will hatch and feed on the ant larvae.Colonies of Atta cephalotes can grow to have ten million workers, all sisters. Here an Atta cephalotes queen sits on her fungus garden, surrounded by her daughters.

Leaf-cutting ants are important enemies of trees in the forests and orchards. But, they are also helpful to plants, and they fertilize the soil with all the vegetation they carry down into their nests.

Leaf-cutting ants have no sting, but they have a powerful bite. One of their enemies is the giant bala ant. Here a bala ant attacks a trail of Atta cephalotes. "Bala" means "bullet" in Spanish. The powerful sting of the bala ant feels like being stung by a bullet.

Some types of leaf-cutting ants do not attack the leaves of trees. Acromyrmex volcanus is primarily a scavenger, cutting the leaves of small herbs and collecting fallen berries and flowers. Here, an Acromyrmex volcanus worker is carrying a fallen flower bud.

In a study featured in the Journal of Chemical Ecology the complex and intricate secretions of the leaf cutter ant, specifically the ant Acromyrex octospinosus, were studied and identified.  The metaplural gland found only in ants has been the subject of much debate in regards to its purpose in the ant's biology.  The gland was first believed to give off secretions of pheromones to mark territory and identify nest mates.  In recent years this theory was replaced with a new one that the metaplural gland was actually involved in antibody defense against microorganisms.  In the Ortis-Lechner and others study featured in the Journal of Chemical Ecology, it was these metaplural gland secretions that they were studying. 

In the Ortis-Lechner and others study twenty-one major chemical compounds were identified!  These twenty-one chemical compounds were identified through gas chromatography, and by testing 138 specimens from three different ant castes (major, media and minor) to get their results. 

So what does all this mean?

From the results of the Ortis-Lecher and others, study of the metaplural gland and its secretions a couple of possible conclusions are reached.  Firstly due to the wide range of discovered acids the metaplural gland secretion can be used to lower the pH in the fungus garden.  This theory is supported by the knowledge that the fungus in garden grows at a pH of five and that if the ants are taken away from their gardens in a matter of days the pH has risen to that of seven or eight  (journal of chemical ecology 26: 1679).  However the acids in the metaplural gland could also have antibiotical uses for the ants or their surroundings.  Needless to say the chemical interactions between the leaf cutter ant and its food source fungus are massive, whether it is the ant adjusting the pH for the fungus to have optimal growth conditions or it is the fungus giving enzymes to the ants to allow the ants to digest usually non-digestible parts of plants.

 

This video documents the picture above showing the various chambers in a leaf-cutters greenhouse. There are chambers strictly for storing various leaves that are composting and the central chamber for the growth of their spores. Pretty good sized kitchen for an ant!