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Leafcutter Ants - The Formidable Farmers of Costa Rica's  Rainforests

When you arrive at Camp Osita, one of the first creatures you will probably encounter is the leafcutter ant (Atta cephalotes). These intrepid forest-specialists can be found across most of Central and Southern America, and are seen across the forests near camp. They are most famous for carrying pieces of leaves across the forest floor, forming massive production lines with ants streaming back and forth taking leaves back to the nest. These incredible insects can travel over a kilometre with their cargo and can clear a path up to 6 inches wide, leaving the forest floor bare on their procession route.

Not all leafcutter ants do the same job though. If you look carefully at a leafcutter ant trail in progress, first you will likely notice the ants actually carrying the leaves. These are called ‘media workers’ and their task is to take the leaf fragments back to the nest. Next, you might notice the ‘soldier ants’. These big, brutish ants are responsible for protecting the workers, fending off potential attackers and keeping the line free from debris. Finally, if you look closely, riding on some of the leaves you will find really small ants known as ‘minima workers’. These hitchhikers play an important role protecting their media worker from parasitic flies, which try to lay eggs on the ant’s neck. If successful, the larvae would bury into the ants head – a rather gruesome way to go! Waiting back at the nest is a single ‘queen’, who will have up to 5 million subjects.

But why are the ants harvesting leaves and walking all the way back to their nests with their heavy quarry? The answer may surprise you. Once inside the nest, worker ants clean the leaves and chew them up into tiny pieces. Then, the ants add saliva and their own faecal matter, which helps to decompose the leaves. Next a special fungus is added to the leaves. This fungus is needed to create the perfect growing medium for another fungus. It is this final fungus which the ants eat. Essentially farmers, the ants grow chambers of this fungus, called ‘fungus gardens’, which can reach 12 inches in diameter and serve as the colony’s food source. In a mature colony, there could be hundreds of fungus gardens connected by a maze of tunnels.

It sounds like a complicated system, but the ants can’t digest the leaves themselves, so resort to this clever system to grow their food. This benefits the rainforest as a whole too. The ants excavate the debris from the nest, resulting in a large mound above the nest. This helps to recycle treetop nutrients back into the soil, which are then available to other forest plants and animals. Leafcutter ants are vital to the healthy functioning of an ecosystem. If you ever get the chance to see them in action, remember just how important these tiny creatures are for everything else in the forest!

By Jack Bedford - Costa Rica Big Cats, Primates and Turtle Conservation Project

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