http://www.youtube.com/watch?v=prjhQcqiGQc
Ants can sometimes get caught in a phenomenon called a spiral of death, in which the entire colony can become lost and disoriented and march in circles until they die of exhaustion. Because certain species of ants are essentially blind, they navigate by following pheromone trails left behind by other members of their colony; they use these scent markers to identify food supplies and find their way home. However, should enough of them lose the scent, they will begin to follow the ant immediately in front of them, forming an enormous death spiral in which they will essentially commit suicide.