Ant science: Thievery persists in a world of plenty


I can forgive people for overlooking the fascinating behaviors of the thieving ant Ectatomma ruidum. There are so many ants with peculiar and amazing features (like agricultural ants, and those with rampaging armies). Some just fly under the radar.

Here’s the latest from my lab.

A few decades ago, Mike Breed and his students were studying behavior, and one part of the work involved using baits to feed ants. He noticed that sometimes, when a colony brought a good piece of bait underground, a different ant took it out of the colony, and carried it in a straight line to a neighboring colony. With a set of careful observations, excavations, labeling workers and some nestmate recognition chemistry, he described a unique phenomenon.

The sneaky thief

The sneaky thief

Colonies of E. ruidum steal from one another, all the time. They have a caste of specialized thieves that spend their time hiding out in a particular neighboring colony. When some good food comes along, they bring it back to their own colony. The best food items move around from one colony to another like uneaten Christmas fruitcake, only everybody wants it instead of passing it off.  The behavior of the thieving has been worked out well by the Breed lab, in a great set of papers. (And, I’m biased, because Mike Breed was my own PhD advisor, the best one I could have had.)

I wanted to understand how this thieving can persist, with everybody stealing from everyone else. This phenomenon makes a jumble of most game theoretical models, because everyone seems to be cheating, all of the time. What makes thieving happen? If they have plenty of food, do they stop thieving?

We ran an experiment in which we gave the colonies as much food as they ever could have wanted. It turns out that the rate of thieving did slow down.

The surprising result was that they kept continuing to steal from their neighbors, even when they had everything they could ever want.

This raises many more questions about the function, evolution and maintenance of thievery. We’re actively working on that, with some work finished and more in the works, and I’ll share more as it comes out.

How this project happened in my teaching institution

I’ve long wanted to work on the ecology of thieving, ever since I helped out on a project with these ants. However, I never had the time to set aside.

In 2008, a friend of mine had a PhD student who was working on poneromorph ants, who was interested in getting some time in the tropics. I was down in Costa Rica with a group of undergrads at the field station, and Benoit Guénard joined us a few weeks. He was a tremendous influence on my students with his enthusiasm, natural history talent, and the most robust work ethic I’ve ever seen. Seriously. We knocked out this project together, with Benoit taking the lead.

So, it took 4 years to get this paper out. In that time, Benoit completed his dissertation on the invasion of the Giant Needle Ant and also has done some top notch work on the macroecology of ant diversity patterns. Once his dissertation was out of the way, he focused on writing up this thieving experiment that we started early on in his dissertation. (I also have a few other collaborations with grad students, and former grad students, that are also awaiting a writeup. We’ll get to them, eventually. There are worse things than a backlog of papers that need to be written.)

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