ABOUT THIS EPISODE
Summary? Can ants be farmers? Join Kiersten to find out!
For my hearing impaired followers, a complete transcript of this podcast follows the show notes on Podbean
Show Notes:
“Tales from the Ant World” by Edward O. Wilson
“Adventures Among Ants” by Mark W. Moffett
Music written and performed by Katherine Camp
Transcript
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Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.
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Kiersten - Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating.
This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.
Can ants be farmers? In this episode we are going to find out. The sixth thing I like about ants is their farming abilities.
You may have heard of leafcutter ants. These are ants that cut leaves and carry them back to their colony. They are often highlighted in nature television programs. It’s mesmerizing and charming watching a line of ants traveling with various sizes of leaf pieces held above their heads. Leafcutters will fall into one of two genera: Acromyrmex and Atta. There are 39 species that we currently know of and they are all found in the New World. Atta are most prevalent in the tropics of South America but there are two species that can be found in North America, one in Texas and Louisiana and one in Arizona.
Leafcutter ant nests can extend 7 meters, or 22 feet, into the earth and contain eight thousand chambers. The largest chamber is typically the ant waste chamber which is buried as far down as they can make it. The title of this episode is farmers so how does that relate to our leafcutter ants? Well, leafcutter ants are farmers. I used to think that they cut those little pieces of leaves to eat themselves, but that is not what they are doing. They take the leaves back to their nest where they feed it to fungus. They tend the fungus like farmers and then they eat the fungus, or rather the larvae eat the fungus. So I guess every leaf cutter ant eats the fungus at some point in their life.
The adult workers ants eat the sap from the leaf fragments that they cut. This is what energizes them to process the leaves. The leaves have to be mulched first before it is fed to the fungus. The fungus will grow and grow and grow in the leafcutter nest. It will fill up the majority of the chambers with a lightweight spongy structure that kind of looks like a human brain and is called a fungus garden. The ants tend the fungus by adding new leaves to the top and sides while they removed the older bottom portions.
It is unusual that ants are completely dependent on vegetation, but leafcutter ants are. The fungus is actually high in protein and that helps the larvae grow big and strong.
The largest nest that Mark Moffett ever came across during his studies was in the Kaw Mountains of French Guiana. The above ground soil mounds were chest high and ranged over a 14 meter wide area. It ranged over about 160 square meters in total. If we compared this to a human made structure, it would be bigger than the Empire State Building in New York City. This nest probably housed millions of workers.
A nest of this size can require an excavation of 40 tons of soil. It must house the queen, the brood, and the workers but even with millions of ants it’s the fungus gardens that take up most of the real estate. The ant population can weigh up to 15 to 20 kilograms and utilize 280 kilograms of leaves. That’s enough plant matter to blanket a soccer field.
Now, this is a lot of living things inside an enclosed space, so it gets hot and humid. To combat increasing heat and humidity which slows down fungal growth, the ants have installed air conditioning ducts. The long tunnels that open above ground are placed strategically around the nest to release humidity and heat. If it get too cold, the tunnels will be closed off.
The only reason leafcutter ant nests can support millions of workers is because they are farmers. Just like humans, farming allows the ants to support a larger population by creating their own resources. These ants use incredibly advanced farming techniques. Humans will use various farming equipment to produce large quantities of crops, but for leafcutter ants its all hands on deck.
The ants within this species are highly polymorphic, meaning sizes between workers vary greatly depending on your job. The largest soldier ant is 200 times bigger than that of a small worker. These colonies are run like assembly lines of self-directed individuals. Many steps are managed by ants in a variety of sizes. Mid-size workers cut the foliage, carry it into the nest, and deposit it onto the garden surface. Smaller ants with 1.6 millimeter wide heads take the next step which is shredding the greens into scraps.The next step is accomplished by even smaller ants who chew up the scraps into moist pulp. Still smaller ants will insert the pulp into the gardens. Then ants with 1 mm sized heads will lick the pulp and seed it with tufts of fungus from established fungal gardens. This is just like a human horticulturist using cuttings from a vine to establish a new crop! The smallest workers with a head width of 0.8mm remove contaminants from the gardens such as bacteria, yeast and spores.
Just like any good farmer, the ants use fertilizer to help their gardens grow. They don’t have to go far to get the fertilizer, they just poop on the leaves. The ammonia and amino acids in the feces helps breakdown the leaves and encourages growth.
To retrieve the plant matter that grows the fungal gardens, leaf cutter ants will maintain almost permanent trails. Other species of ants trails vary depending on where they can find resources, but leafcutter ants are loyal to their grocery stores. Another caste of ants larger than the workers we have already discussed but smaller than soldiers that defend the nest are the maintenance crew for the paths. They will dismantle anything that gets in their way. They haul off debris that they can heft and chew through things they can’t. They widen and smooth out the path until traffic is flowing again. They can do this quickly as they are present on the paths at all times! Boy, don’t we all wish our highways were that well maintained!
There is still one more layer to these superhighways. Worker ants that are smaller than the ladies hauling the leaf parts home will scamper about under the plant carriers and reinforce the pheromone trails. As we discussed before, these pheromone trail are super important for ant communication.
With all of these layers of responsibility, levels of workers, and intricate cooperation, some believe that leaf cutter ants are the gold standard of superorganisms. Quoting from Edward Wilson’s book, Tales from the Ant World, “So well-marked and powerful is the division of labor among members of a leaf colony that individual colonies can be reasonably called a superorganism.” The definition of a superorganism is an organized society that functions as an organic whole. Leafcutter ants must have every layer of worker functioning correctly to survive, any deviation and the whole organism dies.
Edward Wilson goes on to say, “The leafcutters are superorganisms that succeed under natural conditions.”
I think we have established that ants can be farmers and very successful farmers at that! Thanks for joining me for episode six because my sixth favorite thing about ants is their ability to farm.
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Join me next week for another exciting episode about ants.
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This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, my very own piano playing hero.
