Leaf Cutter Ants: Farmers of the Forest

Categories: Belize

Walk through the forests of Belize, and you might spy dozens of small brown ants scurrying across the forest floor, each carrying a single, perfectly cut leaf. These are leaf-cutter ants, a name that applies to a collection of several antspecies native to Central and South America. With powerful jaws that can vibrate thousands of times each second to strength enough to carry up to 20 times their own body weight, leaf-cutter ants are one of the most impressive species of ants in Central America. But what is most incredible about these insects isn’t their physical prowess – it’s their unique form of symbiosis with their environment, one that lies at the heart of their leaf cutting behavior.

A leaf-cutter ant nest is a massive construct, up to 50 feet wide and 16 feet deep, with tens of thousands of ants born from a single ant queen. A hive this large requires enormous amounts of food to survive, and on first glance, it might appear that the leaves these tiny insects are busy harvesting from the surrounding forest might be the source of their food. But leaf-cutter ants don’t actually eat the leaves they harvest. Instead, these leaves serve as a means to cultivate leaf cutter ants’ true food source: mushrooms.

Deep within this network of tunnels and chambers, some up to a foot wide, lies the true fuel of the colony: a massive forest of fungi, fertilized and cultivated by the leaf cutter ants as a source of food. The masses of leaves that leaf-cutter ants bring to the nest each day, estimated to be around 17% of total leaf production in the surrounding area, serve not as ant-food, but instead as a compost to grow editable mushrooms.

Through this behavior, the leaf-cutter ants give the mushrooms a safe and competition-free place to grow – even going so far as to groom the nest to remove other invasive fungi – while the mushrooms provide a consistent and reliable food source for the entire ant population. It’s a fascinating example of symbiosis in the animal kingdom, and one that all 47 leaf cutter species perform from Belize to the Amazon Rainforest.

This relationship is carried from nest to nest by leaf-cutter ant queens, which leave the nest soon after they are born with a sample of the fungi in tow. In fact, ant queens even have a special pouch near their mouth for just this purpose of transportation. After mating, the queen soon burrows underground to form a new nest, using the small amount of fungi she carried with her to start a new mushroom colony and provide food for herself and her first batch of offspring. From there, her fully grown children move on to prune the surrounding forest, using the leaves they harvest to grow more fungi and allow the queen to produce more eggs. A queen can live up to 20 years; during that time, up to 10,000 ants can be living in a single nest simultaneously.

The ants’ forest environment has itself adapted to make sure leaf cutter ants don’t completely decimate the surrounding foliage. By developing tougher or fuzzy leaves, or sticky sap that discourages harvesting, plants ensure that the ants merely prune their leaves before moving on to another tree or shrub. In fact, over time leaf cutter ants can form tiny “highways,” or ruts in the ground that allow for easier movement between parts of the forest, allowing them to quickly travel to and from plants and their nest.

Division of Labor in the Leaf Cutter Population

Within a leaf ant colony, there are three types of ants besides drones and queens: maximas, medias and minimas. Maximas are the largest of the three, serving as guards and soldiers to defend their nest and workers from other invertebrates or even small vertebrates that seek to eat the ants, doing so with powerful pinchers (strong enough to piece leather) and a venomous stinger. At the other end of the spectrum are the tiny minimas, responsible for taking care of the fungi colonies deep within the nest and pruning workers for any parasites they might be introducing to the colony.

Finally, the medias ants rest between these two extremes, and are the ones who do the harvesting of the leaves. Medias have been overserved to work in tandem with one another, with, for example, on ants cutting a leaf while another waits below to carry it back to the nest once it falls to the forest floor. This division of labor along different body types is called polymorphism, and is overserved in several other animal species, including bees and fruit flies.

Leaf-cutter ant colonies are far more than meets the eye: a complex hive system featuring clearly defined castes along body types is paired with a unique symbiosis with neighboring fungi, all of which combined leads to leaf cutter ants as being one of the most fascinating and complex species of insects in the world.

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Images:

  • Leaf cutter trail – Inspire EdVentures, Eric Weber, photographer

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