Why Soldier Ant?
First, it helps to understand something about trophallaxis, the process whereby ants in a colony balance the group's nutritional needs via shared mutual mastication and digestion.
Adventuresome, far-ranging ants will bring bellies-ful of exotic treats (an interesting leaf, perhaps, or a piece of fallen berry) back from their constant perambulations -- and vomit said treats up to share with fellow ants. (Ants who, themselves, may be purging up some different foodstuffs -- kind of an ant-equivelant of "Show me yours and I'll show you mine.") Each ant benefits from having access to a wider variety of nutritional content, and the colony as a whole thrives and survives.
An interesting side-effect of the whole process, however, is that more than just food gets passed along. Trophallaxis is also, it seems, a very effective means for ants to transfer Information. Information about potential danger, a potential windfall, or just information about the lay of the land: what's been traversed, what was found, and where to find it again.
So there you have it. Welcome to my vomit. Please leave some of your own.