African army ants are famous for their ferocity. They can, and do, eat anything in their path. When rival army ant colonies meet, there are border wars. Yet when an army ant queen dies, the ants are “adopted” by other colonies.
This very unusual behavior was
documented in a study conducted by Daniel Kronauer, a junior fellow in Harvard's Society of Fellows. What’s significant about it is that army ants aren’t members of supercolonies, the huge modern ant “civilizations” comprised of directly related ants.
Usually, ants are as aggressive to their own species as they are to others. Kronauer’s study found that the army ants joined the neighboring army ant colonies, lost their distinctive individual odors, and became part of the family.
This is an extremely interesting behavior. These new recruits were not only not killed on sight, which would be the normal response, but evidently “qualified for admission”.
The lack of a queen is probably part of the solution. This is purely a layman’s opinion from an amateur mrymecologist, but the absence of active “control” odors in the queen-less ants may have something to do with the acceptance of the adoptees.
Active ant colonies are invariably busy, using chemical stimuli to issue “orders” to the ant armies. Without a queen, these stimuli would deactivate fairly rapidly. It's plausible that other army ants would be aware that the queen-less ants had no working stimuli. It’s possible that the lack of stimuli may mean that these “odorless” ants seen as less of a threat by the other army ant colonies, like chemical flags of truce.
The behaviors are so utterly different compared to normal ant responses that there must be some connection.
I remember seeing a TV documentary years ago in which colonies of army ants and Leaf cutter ants, quite different species, collided. Both colonies contained millions of ants. The expectation would be a spectacular, all out war. Leaf cutters are big, powerful ants. They’re among the few local ant species which can stand up to army ants, and had a war started, both colonies would have been decimated.
In practice, the two species were in contact for a minute or so, conspicuously
not fighting. The only casualty was one ant, which attacked the others, and was promptly killed without retaliation by its nest mates. A peace treaty, no less. The guy doing the documentary was stunned.
So the question is this:
Can ants recognize command stimuli in other ants?
It looks like they can, and that’s how the army ants survive to be adopted by other colonies.
