Sumo wrestling keeps big ants in line

In a Malaysian ant species, scientists are reporting that the large workers fight among themselves in “spectacular shaking contests.”

The workers of Acanthomyrmex ferox include a class of extra-large hulks, called majors. These female ants do the tough jobs, such as cracking seeds and defending the colony. Like the queen, these workers have six egg-producing organs, whereas smaller workers in the colony have two egg organs. While the queen is alive, the workers’ eggs are nonviable and serve as a food source.

The possibility for conflicts involving majors intrigued Bruno Gobin of Catholic University of Leuven in Belgium and Fuminori Ito of Kagawa University in Miki, Japan. In more than 500 hours of videotaping A. ferox colonies, the researchers caught 79 of what they delicately call “interactions.” In some of these situations, majors engaged in antennal boxing, with one major hammering its antennae against another’s body. More dramatic were episodes of a major mounting its forelegs on the head of another and then rocking furiously, rattling its target.

Shaking bouts have a flavor of sumo wrestling, the researchers say in an upcoming Naturwissenschaften. The majors established a stringent pecking order on the basis of these bouts.

To see how majors behave during a crisis, Gobin and Ito removed the queen from four colonies. Majors clashed more frequently, but the pecking order stayed the same. Also, the big workers began laying viable but unfertilized eggs, which turn into males. High-ranking majors produced more eggs than lowly ones. No major mated and became a queen, but the top major patrolled the doomed colony and ate the others’ eggs.

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