Leiningen is an aging plantation owner in Brazil who employs 400 indigenous workers. Described as having bristling grey hair and a bulky nose, he resembles a shabby eagle. He places absolute faith in Western science, his intellect, and his ability to rationally conquer any natural threat. He maintains a paternalistic attitude over his environment and the people who work for him.

The ants are a ten-mile-long army of reddish-black, flesh-eating insects with razor-edged mandibles and brilliant, cold eyes. They function collectively as a single, relentless force of nature. They are highly organized, voracious, and display a terrifying level of strategic intelligence as they advance on the humans.

The District Commissioner is a Brazilian official with lean and lanky arms. He has lived in Brazil his whole life and understands the severe danger the insects pose to human life. He acts as a foil to Leiningen, exhibiting clear fear and urgency in contrast to the planter's calm arrogance.

The Indian medicine man is a traditional healer among the plantation workers. He uses indigenous knowledge and shamanistic methods to create anti-venom brews and protective salves. His traditional remedies stand in direct contrast to Leiningen's reliance on mechanical engineering and Western science.

The workers are a group of 400 indigenous people employed on Leiningen's plantation. They are generally docile and highly alert, placing immense trust in their employer's wisdom and leadership. They perform the physical labor required to implement the defense strategies against the invading swarm, from digging ditches to operating the dam.