Leafcutter Ants of Costa Rica - MartensGallery

Next to humans, leafcutter ants form the largest and most complex animal societies on earth. 

Watch this short video.

Marching with Determination

"Look at these ants" commented Paul Renner as we were hiking down a steep trail that led to the Pacific Ocean in Costa Rica. With excitement in his voice, Paul said "I was hoping we would see leafcutter ants."

Watching them for only a short time captivated me. I saw thousands of ants carrying small bits of leaves 3-4 times their own body size from the top of a 40-foot tree down its trunk and along a trail that extended for over 100 yards before disappearing into the jungle. Somehow in my formal and informal education I missed learning about these amazing creatures. 

Here's Paul photographing the leafcutter ants as they descend from the top of the tree. 

Leafcutter ants live in huge underground nests connected by tunnels. These nests can grow to 100 feet across with smaller nests radiating out extending up to 6000 square feet and containing an incredible 8 million individual ants. 

So why are these ants so busy carrying leaf bits back to the nest?

Deep within the nest the ants cultivate a fungus garden which is  their primary food source. Think of it as preparing "mulch." 

The fungus garden must remain free of parasites that can cause disease which would wipe out the colony. Thus smaller workers remove microorganisms from leafs when they enter the nest and transport these parts of the leaves to a separate chamber away from the fungus garden. 

In a mature leafcutter colony ants are divided into casts based mostly on the size of the ant, and thus perform different tasks. 

Minims are the smallest workers. They tend to the growing brood of ants.

Minors patrol the foraging columns attacking any predators and care for the fungus gardens.

Mediae are the foragers who cut leaves and bring leaf fragments to the nest. 

Majors, or soldiers, are the largest worker ants and defend the nest and clear the foraging trails. 

Only the queen can produce offspring laying thousands of eggs each day.  Most young ants become workers, but a few males and females are capable of later reproduction. 

Beginning with the rainy season fertile ants leave the nest to take part in a nuptial dance where mating occurs. After mating the male dies and the females goes off to begin a new colony. To do so this new queen digs a tunnel, and carrying a tiny piece of fungus in her mouth starts a new fungus garden. 

It is all quite amazing, and yet the success of a new young queen developing a mature colony is estimated to be only about 2-3%. 

While I photographed these busy ants I observed one ant drop its leaf as it was coming down the tree. Almost immediately another ant going up the tree to get a leaf bit stopped to assist the ant, helping it hoist the leaf back up so it could continue marching on to the nest. Teamwork by insects!

I also saw commitment -- an unfaltering focus on completing the mission to which these ants were born. It caused me to think when we humans help each other, work cooperatively, and commit ourselves to the task at hand, we also achieve remarkable things. 

Rainer Martens, March 2015