The ants pose the greatest of threats to Leiningen, for they threaten to destroy his entire coffee plantation, and kill the peons who work for him as well as himself. These army ants are not small, and they come in biblical numbers.
...thousands of millions of voracious jaws bearing down upon him and only a suddenly insignificant, narrow ditch lay between him and his men and being gnawed to the bones "before you can spit three times."
Not only is there a massive physical army of the ants, but these insects are capable of communicating with one another and, literally, thinking. For instance, they build bridges to cross the ditches that Leiningen has had built around his plantation. If they get across they will literally devour the leaves of every coffee plant.