Facts about Leaf Cutter Ants

The Leaf cutter ant is as fascinating a study as a news stand novel! These large colonies you will see in the rainforest surrounding our research site are made up of tens or hundreds of thousands of inhabitants and have an organizational and work structure just as a major city of humans. But there are several big differences between these ants and our work ethic. First of all, everything in the colony revolves around the queen. There is no more important individual to the colony than the queen, without whom the rest of the thousands and thousands of ants would simply give up and cease to exist.

The colony is made up of various types of ants that physically develop with respect to their function in the colony. There are forager ants that we see on the trails, whose job is to explore out from the colony to find leaf material to harvest and transport back to the colony. The leaf material is reduced to a mulch by the worker ants within the colony, and then used as a substrate material to grow the fungus which is food for the colonies inhabitants. There are giant soldier ants whose job is to patrol the colony trails and passages and protect the colony from intruders. These soldiers are way bigger than any of the other inhabitants and they can bite right through a leather boot so beware when you encounter these fierce warriors. There are cleaner ants, very small ants that are one tenth the size of the foragers. These cleaner ants hitch rides on the other ants in the colony and their job is to clean the pests and parasites from the bodies of the rest of the ants in the colony. There are very tiny bot flies that lay their eggs on the leaf cutter ants and these eggs embed themselves in the head of the ants and eventually kill the ants. The little cleaner ants fastidiously clean up the entire body of the rest of the ants to eliminate the threat of these flies. You can see these very little cleaner ants riding along on the bodies of the foragers when you find these leaf cutters on their jungle trails.

Then there are haz-mat ants that remove hazardous materials from the colony. Just like any big city, the colonies have outbreaks of disease, deaths of older members of the community, accident victims, tunneling materials that need to be removed, organic material that turns rotten, all of which has to be removed by ants that are resistant to the pathogens and risks of performing biological and physical cleanup of the community. This function is performed by what we call haz-mat (hazardous material handlers) ants that are larger, older, with more protective mechanisms. Once you can see inside the colony you can see these haz-mat ants doing their work. And of course there is the queen who provides the meaning of life for the whole colony.

To us as humans, there is a great disconnect to the way we live in that the colony contains only ants that are female functions and the only ant that lays eggs is the queen. Thus the colony thrives with all of these ants devoted to work tasks and not to reproductive tasks. Remember that the colony gets its food from the fungus that it grows in its fungus gardens. The fungus gardens are cultivated using nutrient material salvaged from the forest leaves. Each year leaf cutter ants consume 20% of the foliage produced each year by a tropical rainforest, making them by far the largest foliage reduction system in the rainforest. The ants are able to protect their fungus gardens by manufacturing an antibiotic which provides a protection against pathogens that would otherwise contaminate the fungus gardens thus destroying the food source for the colony. The miracle of this system is that the ants somehow keep their antibiotics viable for generation after generation when our science based pharmaceutical labs are unable to do this and we are running out of antibiotics.

The Nuptial Flight

Now for another amazing aspect of the leaf cutter ant propagation cycle! Once per year, as the rainy season approaches, the queen begins laying eggs which produce male ants and queens. Weeks before the rains come(no one knows exactly what triggers this) the leaf cutter ant nest erupt like a miniature volcano and for several hours there is a constant plume of queens and male ants ejected into the dispersal stream of the eruption. A guess is that there might be some 25,000 queens thrown up into the environment during this phenomenon. These queens then fly on what is called a nuptial flight, up to 7 or eight miles to reach a location far removed from their original colony

These queens are packed with an invaluable cargo for they carry with them enough genetic material to fertilize all of the eggs the colony will produce for the next 25 years, she carries with her a supply of the fungus to replant and start a new crop for the new colony she will create. She carries with her a supply of the antibiotics to inoculate the new fungus garden. The queen is so packed with valuable cargo that of each 25,000 queens that are dispersed into the air, only 5 reach their destination, the rest being consumed by birds, bats and humans(yes, indigenous people sautéed the queens) for the nutritional value packed into these flying food packets. When the surviving queen finally lands, she has been impregnated in flight by 1 or 2 or 3 males who expire after transferring their gene pool to the flying queen. This in flight gene transfer has never been observed but we know it take place due to DNA analysis.

Once the queen lands, her wings drop off and she digs a shallow chamber into the ground and seals herself off from the outside world where she starts the whole process of laying new eggs, planting a fungus garden, and tending the beginning of what will become a giant new city in the coming years. As the colony grows its workers create new passageways, new chambers, new fungus growing gardens, new foraging paths deep into the forest, and a whole new colony that will exist for as long as the queen is alive(about 25 years).

Leaf Cutter Wars

Another parallel to human development is the unenviable characteristic of taking your country to war. The reason the queen flies so far from her original colony is that two colonies who intrude upon one another will eradicate one or the other of the colonies. As the colony grows and the foraging trails extend further and further into the forest there is a greater and greater likelihood that one colonies trail will overlap the trail of another colony. When that happens the results are most bizarre. The two colonies then proceed into a war footing with each other. What transpires is much like a duplication of human warfare in which the ants organize into groups that perform different war functions, such as infantry, armor divisions, etc. The two colonies devise their own individual strategies for approaching their conflict with their enemy colony. For example, the huge soldier ants, of which there are limited quantities, make up the armor divisions. The foraging ants might be compared to infantry divisions. The workers might be logistical and supply divisions. Each day of the war there is a strategy undertaken by each colony. The front line of the battle is located in proximity of the location where the two colonies encountered one another.

For example, the first colony might elect to attach with armor, so the soldier ants are organized into a massive frontal divisional attach marching to overwhelm their adversaries lines. The second colony might have chosen to attach with overwhelming numbers of infantry so the infantry meets the armor head on. While the soldier ants go through the infantry tearing up the individual soldiers with ease, the infantry attacks with the same strategies as a modern infantry encounter with armor. In these cases the infantry attacks each armor(solder ant) with a simultaneous assault by five or ten infantry on the same armor(soldier) so that with an infantry ant on each leg, an infantry ant on each part of the soldier anatomy they cooperatively bring down the soldier. In this case it then evolves into a numbers game as to who runs out of resources first, the armor or the infantry. The days battle usually ends with no clear cut victor so the two sides retreat to each develop a new strategy for the following day . This process continues until there is evidence that one or the other colonies is at risk of resource depletion and when that happens the resource poorer side gives in to defeat and there is a catastrophic relocation of the colony for survival sake.

Colony Relocation

The relocation of leaf cutter ant colonies is another phenomena yet to be understood. From time to time, a mature leaf cutter ant colony decides to relocate itself. This is a massive undertaking for a community of so many inhabitants. When these relocations take place the entire community relocates its fungus gardens, its brood chambers, its tunnel system, its foraging fields, and the entire community of pupa and larva that are in various stages of development. How they do this is an unknown for it has to be like a giant science fiction story moving the entombed living future of the colony. If we were to scale up the ants to approach human scales this would be the same as moving the entire inhabitants of Paris, their homes, their food sources, the city buildings and street system all to Rome in a two week period. How they do this is yet another mystery to be understood.

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Exposing High School science students to tropical rainforest research in partnership with:
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The ant colonies are comprised of a complex caste system in which ants are morphologically separated into groups of different sizes assigned to tasks commensurate with their size. Here is a large soldier ant assigned to protect the an colony from intruders along side a smaller worker assigned colony hygiene responsibilities. There are many different castes within the colony which students need to observe to determine functional responsibilities with which they might design an experiment.
The atta cephalotes ants we study reside in gigantic colonies with up to 8 million individual ants each with their assigned tasks. Here is a typical "Ant Hill" showing one entrance to such a large colony.
Our scientists and grad students from the University of Costa RIca and the University of Wisconsin first perform a surgical maneuver of removing a fungus garden with its host queen for containment in these plastic containers so that our students learn the quite complex procedures.
Here our students carefully transplant a fungus garden from a leaf cutter colony into a container for relocation to the lab, all done with surgical precision and sterilized tools.
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Leaf Cutter Ants – Why Should We Care?

The leaf cutter ant colonies in the forest vary in size from brand new colonies to colonies that have perhaps 8 million ants in the colony. We deal with a species of leaf cutters called Atta Cephalotes. These leaf cutter ants can be seen marching single file through the rainforest with leaf sections twice as large as the ants themselves. These sections of tropical forest leaves have been harvested form the very top of the canopy of the rainforest where the leaf cutters ascend to use their fast cutting lower jaws(mini saws that operate at 1200 cycles per second) to cut the leaf sections from the forest canopy. These leaves are toxic to the ants, never the less the ants transport the leaf sections down the height of the forest trees, along the forest floor to the entrance to the tunnel system that interconnects the various chambers of their colony. Once at the entry to the leaf cutter ant underground maize the leaf cutter turns the leaf over to another worker ant that is more suited to shredding the leaf into a pulverized mass at the same time as the ant creates a new compost pile of shredded material deep into the bowls of the system of chambers that make up the colonies underground city.

Once the material decays it provides nutrients which allows fungus to grow and it is the tips of the fungus that the ants use for food. Thus, we have another species on our planet, beside ourselves, that undertake farming to raise their own crops for subsistence. However, for 10 decades there was a mystery as to how these ants kept their fungus gardens free of contaminating pathogens.

This was a world class mystery until a young PHD student(Cameron Currie from the University of Montreal) came along and discovered that these fungus gardens not only have a deadly parasitic mold(called Escovopsis), but that the ants are indeed producing antibiotics which serve to provide protection to these rainforest ant cities from infections of their massive fungus gardens. Cameron Currie discovered that these ants cultivate a bacteria called Streptomyces which is the source of roughly half of the antibiotics manufactured by our pharmaceutical industry. This remarkable discovery has now given us a new mystery. The antibiotics that our pharmaceutical industry produces can only manufacture antibiotics that remain effective for two or three or four generations. We are literally running out of antibiotics because the diseases we use these against are evolving resistance to our antibiotics faster than we can create new antibiotics to be used against the new strains of diseases. Our population faces an imminent disaster as each year we have fewer effective antibiotics that the year before. We are running out of antibiotics at a rate that should be seen as nothing more than a looming catastrophe. Yet these ants have been successful in maintaining their fungus gardens for 65 million years. How do these leaf cutter ants, with brains the size of half a grain of sand, produce antibiotics in such a way to keep them viable for such a long period of time when as human beings we are not able to even keep our antibiotics viable for 50 years? Pulitzer Prize winning biologist Edward Wilson, who has made his life studying ants, has created the term “Superorganism” to describe what the combined intellectual power of social animals operating in mass with a single social goal can accomplish, feats that seem impossible to us never mind the low level cranium power of a tiny insect. Here is a subject worthy of research, the answer to which would have an obvious affect on the health outlook for every human on our planet. If only these ants could teach us how they do it?