Ant queens are more devious then previously thought

When an ant colony starts its more productive to have multiple queens to produce more workers. After they become successful surplus queens are executed by worker ants until only one remains. Queens can expect to know when there time is up and conserve energy to protect themselves. The Copenhagen team found that queens which were fertile had stronger chemical signals, and were also more likely to be spared execution by workers. Workers therefore appear to be selecting the fertile queen as their ruler based on smell.
http://www.biologynews.net/archives/2010/02/25/plotting_and_treachery_in_ant_royal_families.html