Dr. Dornhaus found that fast ants took one to five minutes to perform a task  collecting a piece of food, fetching a sand-grain stone to build a wall, transporting a brood item  while slow ants took more than an hour, and sometimes two. And she discovered that about 50 percent of the other ants do not do any work at all. In fact, small colonies may sometimes rely on a single hyperactive overachiever.

Why do some worker ants lean on their shovels and let the rest of the workers do all the work? “It’s like students living together  you’ll always find one will have a lower threshold for doing the washing up and will end up always doing it all,” she said.

Perhaps the division of labor  which the economist Adam Smith linked to human achievement  may not be the key to ant success. Possibly, Dr. Dornhaus said, “the lazing ants are resting, or are waiting in reserve in case something goes wrong.” Or the laggards may be cooking up some biochemical nest protection. (All ant species manufacture a fungicide to stave off mold in their nests.) Or, she said, “It’s possible they aren’t doing anything at all.”

Dr. Dornhaus was born in Cologne, Germany. Her father was a physicist and her mother an artist, and, from the age of 10, she wanted to be a biology researcher. A high school whiz in math and chemistry, she breezed through an undergraduate biology degree at the University of Freiburg. From there, she headed to the University of Massachusetts, Amherst, for a year as an exchange student. She worked with Dr. Melinda Novak studying cognition in monkeys.

“We were trying to discover if rhesus monkeys recognized themselves in a mirror as chimps do,” she said. (They apparently do not.) “At that point I knew I wanted to study animal social behavior.”

Dr. Dornhaus returned to Germany to find an animal behavior research group and discovered the Behavioral Physiology and Sociobiology Department at the University of Wurzburg, headed by Dr. Bert Hölldobler, the co-author, with E. O. Wilson at Harvard University, of the classic “The Ants” and the recently published “The Superorganism.”