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Your new neighbors are a different species


Posted on 1st February 2015
Atta cephalotes

Atta cephalotes

 

Atta colombica

Atta colombica

 

I’m back again on my favorite spot on the Osa Peninsula to photograph leaf cutter ants for my sprawling, multimedia project.  I have four short weeks to work with the ants and try to make some magic.

Day one: survey the territory.  Who’s still here?  What colonies have gained or lost since my visit last year?  Who’s new on the block?

After years of relative stability, I arrived in the winter of 2014 to discover a crash of the familiar colonies.  Big, medium, small – they were gone.  Had they died, moved, starved, or lost a war?  It’s hard to know since I missed coming in 2013.  The Vampire colony – massive, war-like and nocturnal – was fully mature in 2008 and probably died of old age.  They were the center of all wars, one by one they picked-off their neighbors.  It was hard to watch, but thank you for the images.

The others?  What happened between 2012 and 2014?  I speculate it was drought.  Now that I’m here this year with normal rainfall I see the difference in the vegetation.  The plant, called perennial peanut (Arachis glabrata) covers a large field at the center of the property where the solar panels are located and this year it is green and full of tiny yellow flowers.  It’s the ant’s equivalent of a salad bowl and sustains far more colonies than would otherwise be possible, especially deep in the forest.  In 2012 this plant was sunburnt and brown.

I try to play Sherlock and piece together what happens in my absence.  The colony I photographed last year for the Scrolls (the only one large enough to work with that year) is still here.  It has thrived and continues to harvest from the same set of trees as before.  In my final post of 2014, I mentioned how odd it was the ants took a long, circuitous route to reach these trees.  This year they are marching on a new direct super-highway, bypassing my old set in the bamboo.  The colony still comes out precisely at 6:00 when darkness falls like a hatchet.  And they continue to be light adverse, comically running away from my small headlight and hiding on the side of their highway.

It’s good news this colony is still here.  At least I have one I can use.  I prefer, though, to find a line of ants working the day shift.  Night is tough and scary.  It’s when the all-too-abundant and all-too-venomous Fer-de-Lance comes out to hunt.

Of the colonies I have seen come and go over the years in this kingdom of ants, all have been Atta cephalotes, except one, which was Atta colombica.  A.cephalotes is the most widely distributed leafcutter ant species and A. colombica is more rare.  They look similar.  It’s hard to tell the difference with the naked eye.  But, through the macro lens of my camera and especially once the image is enlarged and printed I see a marked difference.

A.colombica is darker, more magenta in hue.  Its exoskeleton is mat, faintly textured and absorbs light.  On average, the ants are smaller.  None of these characteristics are preferable.  In contrast, A.cephalotes is a luminous, golden brown with a shiny surface that glows under the lights.  The ants are also slightly larger, and in this macro world, even a small size increase helps me focus the camera.

In the field, the most obvious point of distinction is how they handle their garbage.  A.colombica tosses their trash outside.  They make massive refuse dumps, sometimes dramatically so, dropping remains of spent fungus and biological waste from a high point.  The garbage tumbles down like a waterfall.  Overtime these piles grow and accumulate like sand dunes on the jungle floor.  In contrast, A.cephalotes is tidy and buries its waste.

2010 was the only year I worked with A.colombica.  A large colony that lived across the creek and up a steep hill sent a long line of ants my way to harvest from the perennial peanut in the open field.  It took me an afternoon of climbing through tough terrain in snake boots to locate their distant home.  The field must be an extraordinary draw for these ants to risk drowning and cross the creek.  One day after a rainstorm I found hundreds of thousands of them stranded on a log floating in the creek.

A.colombica features only in two works – the second half of “The Chosen” video and in the “Offering” photographs.  By 2011, this colony was gone, but its conical mounds still remain as evidence of a past civilization.

Day two: I surveyed the rest of the area and found many new colonies.  But to my amazement they are all A.colombica, twelve of them.  Incredible.  Judging by their small refuse piles, they are relatively young.

It’s also the first time I’ve seen a colony dig their underground home in the open field.  Previously, the ants that harvest there live on the perimeter, anchoring their homes near a tree, rock or bush.  A.colombica moved right in, digging exit holes open to the elements.

The other weird thing I noticed, when I follow the various lines of ants – I do this to locate who they are, map where they live, identify their foraging routes – many of the pathways are confused.  It looks like a freeway interchange instead of discrete highways.  Lines from seemingly different colonies are passing uncharacteristically close to one another.  If the ants are unrelated, I would see evidence of wars, but I do not.  Some ants carrying foliage are even traveling in opposite directions on the same line, lines headed towards home bases too far away to be the same colony.  Do underground tunnels connect these distant holes?  But, the colonies have too few members to command such a large footprint.

It frankly looks like the new A.colombica colonies are related.  They seem oddly tolerant of each other’s presence.  Maybe the new queens are sisters originating from the same colony.  Or the males they mated with are brothers.  Has A.colombica evolved the ability to permit multiple queens like the Argentine ants?  It is a strategy that has made them an extremely successful, invasive species.

Stay tuned for next year’s update of the Atta Chronicles.



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