Leafcutter Ants

While lots of people hate ants, you can't go wrong with leafcutter ants. I mean, you have to wonder how a single colony can harvest all the leaves of a single mature tree over night and individually carry leaves 50x their own weight. In this article, I will answer this and many more questions that you have. But first, we need to start with the basics. (Note: This article contains a lot of information on leafcutter ants, but not all of it. The world of ant is very big and complex, too much to fit at once.)

What Are Leafcutter Ants

For those who do not know what leafcutter ants are, they are one of the strongest types of ants in the world. They are unique as leafcutter ants perform a kind of "agriculture". Hence the name, they cut leaves and carry them to the nest but not to eat those leaves. Tiny workers called minims chew up the leaves and use the chewed up leaves to fertilize/feed special types of fungus that cannot grow any where else in the world. So why do the ants feed this fungus? Because this is the only food source leafcutter ants can eat from. The reason they can eat only fungus is that thousands of thousands of years the ancestors of this ant found this fungus and started taking the advantage of the fact of not having to hunt and having lots of food still in the winter, just like humans. The thing is they got so used to eating the food the fungus produces, their body evolved to be able to process that single food only. Their are three different genera of leafcutter ants, acromyrmex, atta, and amoimyrmex. They have many differences but what you need to know is that atta ants produce the most workers in a colony life time then the other two genera, has more caste than the other two genera, and one species, atta texana, is the only leafcutter ant recorded to accept more than 1 queen in a single colony. Some species of this genus can grow to at least 18mm long which is almost twice the width of a dice. In this article the information is mainly referred to atta texana ants. But now, how does the journey of our ant begin?

Nuptial Flights

Every colony begins with a queen ant's nuptial flight. Atta queen ants and all other leaf =cutter ants fly only in perfect weather like a warm cloudy day, little to no wind, and high humidity in the surrounding air. It's extremely important that the queen ant flies in good weather with no predator or wind otherwise they'll either have no good land to plant fungus or get scared and loose their fungus pellet stored in a pocket in their throat. And because they need an area with good weather and lots of leaves, they mainly live and reproduce in South America, more in the forested areas. But anyways, during nuptial flights queen leafcutter ants will mate with around 4 different male ants so they can have that wide range of workers. Once the queen ants mate they'll find some moist, well-drained soil, and dig there usually with other leafcutter ants (assuming they are atta texana ants). But now the question remains, how can they successfully start and raise a colony with a 97.5% chance of failing looming over their shoulders?

The Colony Begins

Once the queens have dug their chamber and cover the roof, spit out their fungus to start the farm. That is where one advantage to have multiple queens kick in. Even if 1 or more queens in that group lost their fungus, they can still thrive and lay their eggs if at least of the queens kept her fungus. As soon as they lay eggs the brood will take 6 weeks to grow into minims, like the ones mentioned before. But before they turn to workers, during their larvae stage the queens do something brutal. Since they have to feed some of the internal proteins from the useless wing muscles to the fungus, they don't have enough food to feed the larvae. So any extra eggs that get laid while the minims are larvae gets eaten by the minim larvae. After about 17 days the larvae becomes a pupae then a worker. once they are workers they stop sacrificing eggs and just take care of the fungus and feed from it. After a week from when the minims became workers, they start digging tunnels to the outside world. But that's not the end of the story, what happens next?

Expanding The Empire

As the colony starts to grow and new queens start joining the colony, enemies start taking notice of their luxury. Especially army ants, the leafcutter ants' #1 enemy. Without proper defenses a passing army ant colony could destroy everything they have. So they start making majors and super majors. These ants are beasts with bite force 80x stronger than a minim. They also allow once hard to clear pathways easy to clear. They are strong enough in fact that they can pierce human skin. But why do they need both super majors and majors? Why not just super majors? Well in the world of ants the bigger an ant, the duller their mandibles. So if you had two soldier caste, one slightly smaller than the other, you have one that can easily slice things like enemies and food while the other can be used as last resort tanking any attacks and blocking tunnels. Now soldiers are great and all, but what about food and construction? Since majors are tasked to clearing paths and defending entrances while supermajors defend the inside tunnels, the minims are the only ones able to gather food and construct the nest. And creating the soldier castes require tons of more room for the fungus and ants themselves which the minims can't keep up with. So the queens order a new caste to be created. This caste is the mediae cast. These nimble workers can carry larger quantities of leaves and are small enough, but still strong enough, to quickly construct the nest. This also allows minims to focus on the fungus and work on a new job, sitting on the leaves the mediae carry and ward off parasitic flies that like to lay their eggs in the faces of defenseless mediae workers carrying leaves. Now that all the caste are created, how do these workers harvest the leaves and what kind of leaves do they harvest?

Obtaining The Food

Leafcutter ants are notorious for cutting all the leaves on a plant in just a few hours. In fact they can strip all the leaves of a full grown tree, usually plum trees or peach trees overnight. But they don't take any leaves. They have to pick the best ones otherwise it could endanger the fungus. That's why they are always looking for new leaves. The moment a worker finds a sweet, tender leaf they call other ants not through chemicals but stridulation that makes kind of chirping sounds that even humans can hear. They can do this by the stridulatory organ which you can imagine it like the instrument washboard. The ant has a kind of file on its gaster that the ant scraps against the stridulatory organ. Now let's say they find a good leaf, how do they cut this leaf? That's like cutting a flexible sheet of dense iron with just a pair of scissors. Well they use multiple strategies, like their stridulation. Yes, leafcutter ants use stridulation to actually stiffen the leaves to make sure it doesn't just bend out of the way as they cut the leaf. Especially when they cut it in a way so that one of the mandibles are anchoring onto the leaf while the other drags along cutting the leaf. And also remember the mediae workers? Their mandibles are better for cutting leaves and tougher than the minims' mandibles (like it wasn't tough enough, these mandibles are a mixture of protein and zinc making them as durable as a stainless steel knife). Once they have cut the leaves they'll go back to the nest making a trail with a surprisingly low amount to chemical, 0.4 picograms or 1 trillionth of a gram of this chemical at the very least, so other ants can find the leaf and clear pathways for each other if they need to. They found their leaves so they can have lots of fungus, they have a booming population, they seem to be living a happy life. But in the ant world, there is no luxury. What will they do in the face of danger?

The Foes Appear

(Note: Before you continue reading be warned that this section is mainly about how the army ants will attack leafcutter ants. If you want to see how the leafcutter ants will defend their nest, skip to the next section.) Like I've said, it's impossible for an ant colony to be super successful and remain unnoticed by enemies. That's why the leafcutter ants have soldiers after all. Danger bounds to lurk anywhere, especially when your #1 enemy is the wandering army ants. Army ants are a true danger to leafcutter ants, known to destroy any living thing in their path and feed to their larvae. And leafcutter ants to them, is a feast just sitting right there. So the army ants create a nest using their own bodies and then once they start, the army ants march in waves barging right through the front door. See, army ants rely on numbers and strength. So when they charge they don't actually have a proper plan. But they do have higher numbers and majors, allowing them to quickly immobilize leafcutter majors, running them over and breaking in. So how can leafcutter ants defend against this flood?

The Foe's Defeat

Leafcutter ants with their high complex systems have many ways to beat army ants. They are so successful in defending their home fact that only 1 army ant is known to be able to destroy leafcutter ants, Nomamyrmex esenbecki. So first whenever the leafcutter ants discover army ants attacking, they quickly sound the alarm sending out majors and some mediae to defend the nest. Both ants have the same methods of war in their heads, if a major say from the army ants manage to pin a major from the leafcutter ants, regular army ants will shred the major. And same thing the leafcutter ants will do. While they are battling it out super majors will quickly block the entrances using there thick armor to keep any sneaky army ants from getting in. The remaining mediae in the nest would also have started collapsing tunnels leading to the queen and fungus, eventually collapsing the tunnels leading to outside locking out the battle and yes, their own ants. While locking the other's outside would mean they'll eventually die by the army ants, it keeps the army ants from invading the nest. But what happens when a few army ants manage to break in and survive just long enough to transfer a fungus killing mold? How will the ants keep the parasite at bay?

Disinfecting The Fungus

It's life threatening for these ants to loose their fungus, especially because this parasite spreads quickly and can even kill workers directly. This is why leafcutter ants keep Actinobacteria on their bodies to quickly kill the parasitic mold (called Escovopsis). After applying the Actinobacteria, the ants will remove any fungus killed by the parasite and allow the older workers to get rid of it as the older workers aren't really valued anymore by the colony. To make sure the fungus doesn't get infected again by any parasite probably on the older workers' bodies, they do not allow them to get anywhere close to the leaves, queen, and fungus. The ants will even kill the older workers if the worker attempts to break those rules. But even after handling the army ant waves, the parasite, and trash, they still have to meat a new foe, the weather.

The Uncontrollable Problem

Remember how the workers got rid of trash through their older workers? Those older workers are also confined to hot, deep chambers underground with dangerously high CO2 levels. The problem is that this high CO2 will come up to the other ants and the heat will kill the fungus. So the ants created vents to specifically allow CO2 to flow out of and temperature to stabilize. Their real danger is the rain. Leafcutter ants do not have many strategies to defend themselves against rain but while it may seem like the end for them when rain starts if they are not prepared, they actually do quite well. Because they live very deep underground any rain water traveling towards them, if their small hole manages to bring down any, gets absorbed quickly by the loose dirt. If there is a massive rainstorm that manages to infiltrate all the way into their chambers they'll simply float till the dirt manages to absorb all the water. And because the fungus repels water, the chambers with fungus will be all dry once the ants come back to the chambers. This is why the ants always make those chambers where they keep brood and the queen as they remain dry. The only way the rain can kill the colony is if it stays in the nest long enough to rot the fungus and/or drown all the ants. These ants survive have survived so many dangers and while these succeeded, many other colonies would have been defeated by one of these challenges. But what happens next?

The Victory

There is no doubt every leafcutter ant colony has faced all of these challenges. But the real question is that can those colonies survive the challenges? Usually not, remember these ants don't only face each challenge once in a life time, it happens frequently almost continuously. But colonies that do successfully survive and live to tell the tale grows stronger and learns. Leafcutter ants are probably one of the most advanced ants in the world which wouldn't be surprising if you know how difficult they are for nature to kill (which you by know now). Their colonies will grow so large, especially for multi-queen accepting species like atta texana that people call them ant towns. But wait, don't leave yet, check out these amazing websites and videos that provided me tons of information to make this article possible.

https://pmc.ncbi.nlm.nih.gov/articles/PMC5620700/#B32-insects-08-00080 https://en.wikipedia.org/wiki/Atta_(ant) https://www.youtube.com/watch?v=uNJYgjnk514&t=214s https://www.antwiki.org/w/images/e/e4/Kubik%2C_T.D.et_al.%282024%29_Fight_or_Flight_%2810.3958%40059.049.0328%29.pdf https://repository.si.edu/server/api/core/bitstreams/f56e33df-3f6a-498b-9a35-bde8a958d78c/content https://asknature.org/strategy/bacteria-fight-fungus/ https://www.researchgate.net/publication/248373454_Waste_management_in_leaf-cutting_ants https://ccb.ucr.edu/news/2018/12/17/leafcutter-ant-colonies-may-be-overlooked-source-carbon-dioxide-emissions-new-study https://www.sciencedirect.com/science/article/abs/pii/S0012825223003392