ARMY ANTS: A LESSON IN COMPLEX RELATIONSHIPS   Leave a comment


Veridion Adventures. Philip Davison. Rainforest animals. Rainforest plants

Today was a day of sunshine and showers.  I had a tour in the morning and so off we went into the forest.  The group I had out had never been to Costa Rica and had never visited a rainforest.  They were keen to learn something about this amazing ecosystem.  All the paths on their Internet research had led then to one place, the Osa Peninsula.  So far the experience had proved to be over and above their expectations.

We were walking through the forest and I was explaining the complex web of interactions, the sum total of which comprise a rainforest.  Being in situ and having physical props to illustrate the intricate relationships that exist here always helps give people a better understanding and a means by which to remember it all.

As we rounded a bend and crossed a bridge over the creek, we were confronted by a frenzy of highly animated birds.  This was a large mixed flock of birds from many different families, genera and species.  There were birds everywhere, perched momentarily on the branches, clinging briefly to the trunks, flitting here and there, dropping to the ground and then up again, all of them calling excitedly.  This behavior indicated only one thing; Army Ants, (Echiton burchellii), were on the move.  As we walked up the slope, the heralds of an advancing Army Ant column were there to announce their presence; Grey-headed Tanagers, (Eucomectis penicillata).  Wherever there are Grey-headed Tanagers, you can almost guarantee there are Army Ants.   Sure enough there they were, thousands upon thousands of ants marching in determined fashion in a series of well defined columns, flowing like small rivers made up of living insects, their only goal, the harvesting of all small form of forest life as food for the colony.

These feeder columns will then spread out into a front sometimes 60 feet across.  Army Ants are one of the top of the pyramid predators in the forest; they rank alongside Jaguars, Pumas, Harpy Eagles and Boa Constrictors.  They are a nomadic ant, they have to be nomadic because being such a super efficient predator, if they were to settle into any one location for any length of time, they would very quickly deplete it of all forms of life; spiders, scorpions, centipedes, cockroaches, crickets, small frogs, small lizards, small snakes, fledgling birds, if it is there the ants will have it.  All the carved up remains of the prey is taken back to the ant bivouac to feed the larvae.

During the dry season if an Army Ant colony is moving through the forest as a front 60 foot across, you can hear it coming.  It sounds like light rain pattering on the dead leaves.  Advancing towards you will be a living wave of black death.  All the excited bird activity is not due to the birds feeding on the ants, but rather on the insects that are being scattered as they run for their lives.  There will be woodcreepers, woodpeckers, antbirds, antshrikes, antpittas and those obligative followers, the Grey-headed Tanagers.  If you stand on the path running by your feet you will have crickets, beetles and cockroaches all fleeing for their lives.  And that is what we were witnessing here and now in front of us.  We were in situ and having a live visual performance enacted for us to illustrate one of the intricate relationships that exist here. This is one experience I don’t think those visitors will forget.

Army Ants; A Lesson in Complex Relationships

Well if it is not bad enough trying to photograph snakes, you should try photographing ants.  Unless you find some on a tree trunk at eye level, you are going to be lying on the ground.  I use a ground stand that allows me to fix the ball head.  But it is not easy to see through the viewfinder so now I have to use a right angle view finder attachment.  I like to capture as much detail as I can so I need a good depth of field which means a tiny aperture, f/32.  Now I need a lot of light which is where those five flash units come in.  Taking photographs of the Leaf-cutter Ants or the Army Ants means lining yourself up with a moving column but because you are only 2 or 3 inches from the subject the field of view is going to very small.  So as an ant hurries past the front of the lens you have only got a microsecond to hit the shutter.  I normally just focus the camera on a point and hope the ant is the correct distance away.  Once everything is set up I sit back, try to gauge when the scurrying ant will be in shot and use the cable release to take the photo.  It all sounds very easy doesn’t it?  It is a very hit and miss affair.  For every half decent good photograph you get, there are probably many more that you have to commit to the discard pile.

Army Ant stand off

Army Ant stand off

Nest Raider

Nest Raiders

Army Ants are voracious predators.  They will enter the nests of other ants and sack it of everything; eggs, larvae, pupae, workers and queen.  The only ants they will not interfere with under any circumstances are Leaf-cutter Ants.  There may be 500.000 in an Army Ant colony and up to 8,000,000 in a Leaf-cutter Ant colony.  Anyone who has experienced the flesh carving abilities of a Leaf-cutter Ant soldier will testify to the fact that they are not something to mess around with.  The Army Ants would lose so many of their own numbers trying to raid a Leaf-Cutter Ant nest that they will give them a very wide birth, even if they come across them on the trails.  That was the situation here.  There was an injured Leaf-cutter Ant near the moving column of Army Ants but they would not attack it.  The super mini predators backed off and faced the one struggling individual but would not engage with it.

Philip Davison Is a Biologist, Writer and Photographer Based in Costa Rica

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