Pogonomyrmex Barbatus Harvester Ant Colony Moving Day in Cochise County

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I’d never seen a major ant colony move from home to home before. The harvester ants (Pogonomyrmex barbatus) living in what we call Big Colony did that today. They’d been stable, located about eight feet from our largest gasoline powered generator, for at least the past two years, a community most likely numbering a thousand or more of the big headed red insects.

Why did they decide to pull up stakes? We don’t know. The daily earth-shaking rumble of the big gennie could have had something to do with it. In earlier times, that power producer for our off grid home near the Mexican border in southern Cochise County, Arizona, had only been used weekly at most, primarily on laundry days to run the washer and dryer. A few weeks ago, that changed when we decided to shift to that machine to operate my wife’s window air conditioner. It could have been that.

On the other hand, the new home they’d selected was closer to their primary food source vegetation, so that’s a possibility, too.

Their move only covered a distance of 20 feet or so, no big deal for a harvester ant. Our locals often forage for three or four times that distance from their home base. It did get them twice as far from the noisy generator, though, eight feet away from Home #1 and 16 feet away from Home #2. It also meant I would no longer be tromping my big feet across their primary foraging trail every time I went out to start, stop, or service the generator, so…

The discovery of their move presented me with a dilemma. I was running late, needing to drive to Sierra Vista to pick up several of Pam’s meds…yet it had taken me 70 years of living to witness such a mass move by an ant colony even once. In the end, after three or four entire seconds of indecision, I strode to the Border Fort to get the camcorder.

Talk about frenetic activity. These are some truly committed ants!
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It’s hard to pick out in the camcorder shots, but watching the migration with the naked eye was hugely educational. A few of the ants seemed to be carrying other ants. The passengers certainly weren’t all queens. These ants will carry carcasses of their own back to the nest for consumption, but not all of those being carried looked dead, either. Not sure what that was all about.

Big Colony moving day.  Our most notable Pogonomyrmex barbatus harvester ant family leaves the primary entrance of their old home (above) en route to new digs 20 feet closer to Mexico.

Big Colony moving day. Our most notable Pogonomyrmex barbatus harvester ant family leaves the primary entrance of their old home (above) en route to new digs 20 feet closer to Mexico.

Traveling at their usual bat-out-of-Hell harvester ant pace, hundreds upon hundreds of workers transfer food stores and even a few passenger ants to their new digs.

Traveling at their usual bat-out-of-Hell harvester ant pace, hundreds upon hundreds of workers transfer food stores and even a few passenger ants to their new digs.

With video in the can and a few photos in the Canon PowerShot, it was off to town…but of course I had to check in with the ants after I got home around 1:00 p.m. What might they be up to now?

At that moment, it was all quiet on the harvester ant front. There was no action whatsoever near the old colony entrance…but there was something interesting going on at their new home. A few ants at a time, from one to five or so, would come zipping out of the main hole, zipping along–for an average of three inches or so, whereupon they’d do a perfect about face and go zipping back to the hole. The activity, such as it was, seemed to be nonstop. I watched for several minutes, puzzled.

Not until that evening did it hit me what they were doing. They were serving as the colony’s thermometer! It was too hot outside for ants to be foraging on long distance runs. We’ve all heard of those evil little boys who think frying ants with a magnifying glass is a fun thing to do. (I’d like to fry those boys a tad, but that’s another story.) The thermometer was hovering around ninety degrees under a blazing southern Arizona sun. The ants were running out just far enough to say, “Okay, still too hot to go back to work!”

Most likely, the “hot ants” got to hang out under cover to cool off while others took up the rotating temperature gauging duty. Mercury, shmercury; ant colonies–at least Pogonomyrmex barbatus harvester ant colonies–have their own built-in biological thermometers!

This theory received an extra bit of validation later in the day and also today as further observations were made. When clouds began to roll in, obscuring the sun but not automatically dropping the temperature, the “thermometer ants” continued taking the temperature–but with the sun hidden, they were able to travel as much as six to eight inches from the nest before retreating. “Still too hot, boss, but getting better. A bit more siesta….”

When the early evening arrived with temperatures that dropped down into the low eighties…hundreds of the foraging workers got back at it.

Late yesterday, there were still a relatively few ants finishing up at the old hole. By midnight, when I shut down the generator and took a final look for the day, Home #1 appeared to be fully and forever abandoned, not a single ant anywhere near the holes (there are three for that colony, the main entrance plus two smaller entrances). Home #2, however, showed significant activity in the immediate area around the main entrance; there was a continuing “fistful of ants” doing whatever they were doing–possibly guarding the new palace against possible invaders from the Ant Aggressors’ Alliance or some other evil entity.

Home Sweet Home:  Beautiful new quarters for the harvester ants of Big Colony in southern Coschise County.

Home Sweet Home: Beautiful new quarters for the harvester ants of Big Colony in southern Coschise County.

Update: Early evening, one day later. The move from the old home is not quite complete after all. In the cool of deep dusk, a hundred (or maybe two hundred) ants were finishing up, hauling more “stuff” from Home #1 to Home #2. Egg cases seemed to be part of the cargo.

Update: Midafternoon, July 29, 2014. I got it wrong. The harvester ants were not moving; they were expanding the colony. Today, from the “old hole”, hundreds of winged queens and their orange colored but equally winged male consorts emerged for the single mating session scheduled each year. A post on that will be published shortly.

5 thoughts on “Pogonomyrmex Barbatus Harvester Ant Colony Moving Day in Cochise County

  1. This is fascinating, Ghost. I love the editorial along with the video. I wouldn’t have a clue what they were doing without your questioning mind. Pretty cool!

  2. Very interesting Fred . I think the ants carry each other so one can rest etc.,but not sure. I see you got a real camera now. Roy

  3. I certainly find them fascinating, Sha. Of course, I could always be wrong about what it is they’re really doing, but so far they make sense to me.
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    Roy, I figured you’d notice the camera quality difference as soon as I saw it was you commenting. It’s still a point and shoot but not bad at all, a Canon PowerShot SX260HS with 20X optical zoom before getting into the image-degrading digital zoom. The case rides at my left hip every hour I’m awake.

    I never thought about the ants resting by being carried. Could be, though, or maybe they get a free ride if they call in sick for the day. It’s not a high percentage of them in the passenger category, but I noticed a dozen or so during just a few minutes of observation during the peak of the moving activity. Some were carrying egg cases, too, but that was to be expected.

  4. Well, I’ll be jiggered. You are definitely correct, and now I get to correct this post. Except for the video; I’m not about to try re-narrating that. Thanks for the clarifying eyeball.

    My misidentification of the species was, I suspect, a classic example of seeing what one expects to see. We had a very active colony last year (until it got wiped out) of Pheidole tepicana…and I’d always “assumed” this bunch was “more of the same”. Of course, we know what “assume” does….

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