[Science and the world of tomorrow] Mutated African siafu (army ants) on the loose in a metropolitan area, what ruckus would they create?

Say, some entomologist (be he or she a hired gun of some company or not) was doing test to see if siafu could be somehow utilized as an organic pest control. Through genetic manipulation create a mutated line of siafu that was as large ‘D’ cell batteries and hardy enough to withstand temps as low as 52 deg. Fahrenheit. If some got loose into the wild (as these things sometimes happen) and started mating and among themselves and crossbreeding with regular ants and fire ants, creating huge colonies of fierce attacking ants, how would that effect a metropolitan area? Would it be incumbent to the size of the metropolitan area or proximally to open spaces or large parks? What if it were simply an urban area in or near the hills or woods? Once the genie was out of the bottle, so to speak, would there be any remedy for them, or would man just have to deal with them as Africanized killer bees?