You may be thinking, "What's with the title?"
Well, it's three of the evolutionary reasons for "army ant syndrome" which may be the cause of the ant death spiral (or less sensationally known as the ant mill). Check out this video.
It's apparently caused by some wayward ants following a pheromone trail. One follows another and so on until they begin spiraling around a central point. Eventually, either the mill is broken, or all the ants die from exhaustion (check here for a concise description as well as links to primary research).
You may also be interested to read this entry by Frederic Delsuc which has a very interesting explanation about why this behavior hasn't been selected against. It seems that this is the trade off army ants were stuck with. They got collective foraging ability and paid for it with the possibility of one ant causing an entire colony to all skate right to their deaths.
