About 50 years ago, during drought conditions here in New England, I happened to catch sight of a dense column of ants maybe two feet wide and some 35 feet long was marching East across my side yard. Leading the column was a near perfect circle about a meter across, defined by slightly different ants that traveled as though contained by a moving circular boundary. As each ant reached that boundary at some certain angle, it snapped into an equal angle away from the circle. They might always have all been always been turning to their right. They raced around and around with those segments of travel, swinging around in their headings even into reverse direction.

 

In disbelief I tracked them across the street where a water ban violator had lush grass through which the left me staring at their departure.

 

Can anybody advise me of what was going on?

These?

http://en.wikipedia.org/wiki/Army_ant