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Study Finds Most Ants In A Colony Are Slackers


Ants - champion weightlifters and builders, soldiers, queens, drones, all toiling diligently to populate and maintain colonies, which for some species can span miles. And then there are the slackers - that's right, there are lazy ants down there. Dr. Anna Dornhaus is an associate professor at the University of Arizona, and she's involved in a new report identifying idle ants. It was just published in the journal Behavioral Ecology and Sociobiology, and she joins us now.

Welcome to the program.

ANNA DORNHAUS: Thank you very much.

SIEGEL: Who are these slackers and what are they not doing?

DORNHAUS: Well, it actually turns out they're the majority of the ants. This is something that we have been describing previously very informally, but now we've really nailed it down and showed that most of the work is done by a very small fraction of the ants in the colony. So a large number of ants actually don't seem to participate in all that work that you were describing.

SIEGEL: They're just hanging around, or giving moral support? What are they doing?

DORNHAUS: (Laughter). Yes, we think that they are not lazy for some kind of selfish reason that they want to slack off or just relax and watch TV, but they are really not doing anything at all. They're just standing there motionless. And our new idea is that we think that that inactivity actually plays a crucial role in the organization of the colony as a whole.

SIEGEL: How is that? How would the inactivity of the majority of ants play such a vital role?

DORNHAUS: Well, there are probably are multiple explanations, but what I find particularly interesting is that we have shown that in order to make sure that the right number of workers are allocated to all the particular jobs that have to be done, it's beneficial if the colony has some excess workers - essentially, extra workers, more than the number that they need to get the work completed because it just makes that process run more smoothly - of actually figuring out who has to do what.

SIEGEL: So you have discovered the theory of surplus ant labor, is what you have found.

DORNHAUS: Yes, indeed. It's also possible that they are, in part, storing food. So these ants that are just standing around may actually have full stomachs, and not just for themselves, but they regurgitate food to other ants when they need it. But we think that the main explanation has to do with this structure of how the colony's organized.

SIEGEL: And are these ants - who you assume would be - inactive throughout their entire lives, or have you discovered retired ants in these colonies who used to do something else?

DORNHAUS: These particular ants that we're studying, they actually live for a few years, so we have an ongoing study trying to find retired ants (laughter), which is quite possible that some of them are senescing and therefore not able to work as much as the other ants.

SIEGEL: I read a description of what you did here, and this involved actually painting - with very small dots I assume - painting the ants to track their behavior over several days.

DORNHAUS: Yes, indeed. And that is one of the major activities that my students are doing over the summer, so we take these individual ants, which are about three millimeters long - that's about the size of a capital I on your printed page - we briefly anesthetize them, and then under a microscope with a very thin wire, we paint each individual ant with an individual specific color code so we can recognize them.

SIEGEL: Are these graduate students, by the way, or are they undergraduates who are painting the ants?

DORNHAUS: Both, and actually even post-docs and sometimes high school students.

SIEGEL: Oh, really?

DORNHAUS: Everybody gets to take part in the joy of painting.

SIEGEL: (Laughter). Dr. Anna Dornhaus, of the University of Arizona, oversaw research on lazy ants that was just published in the journal, Behavioral Ecology and Sociobiology.

Thanks for talking with us.

DORNHAUS: Thank you very much. Transcript provided by NPR, Copyright NPR.

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