In 1954,
New Mexico State Police Sergeant Ben Peterson and his partner, Ed Blackburn, discover a little girl wandering the desert in a catatonic state near
Alamogordo, and the ravaged and abandoned travel trailer she came from a few miles away. The officers summon an ambulance for the girl, and, while the scene is processed, go to a nearby rural general store. They find it destroyed in the same way as the trailer, and the owner's dead, mutilated body in the cellar. No money was taken at either crime scene. Peterson leaves Blackburn alone to wait for backup, and Blackburn hears a strange, pulsating sound outside. He investigates, and empties his gun at something before screaming in agony. The owner of the trailer is found to be an FBI agent, so Agent Robert Graham is called in from the local FBI office to help Peterson. He sends a cast of a print found near the trailer to Washington, D.C., for analysis, and is surprised when he receives word that Drs. Harold and Pat Medford, father and daughter
myrmecologists, are being sent by the
Department of Agriculture. On an educated hunch, Harold exposes the little girl to the scent of
formic acid, which is characteristic of ants. The odor releases her from her catatonia, leaving her shrieking in panic, "Them! Them!" Peterson and Graham take the Medfords to where the trailer was found. While searching the area, Pat is accosted by a giant foraging ant, and Harold directs Peterson and Graham to shoot off the ant's antennae to blind it, before Peterson kills it with a
Thompson submachine gun. Harold theorizes that the ants were mutated by radiation from
the first atomic bomb test near Alamogordo, and have turned carnivorous from lack of a suitable food supply in the desert. A helicopter search of the desert discovers a giant ant nest, surrounded by human remains.
Cyanide gas bombs are tossed inside, and Graham, Peterson, and Pat enter to explore. They are attacked by a pair of surviving guard ants, which they dispatch with
flamethrower and Thompson. At the lowest level, Pat finds evidence that two queens have hatched and flown away. Harold declares that, if the queens are allowed to establish new colonies and the ants continue to spread, mankind may cease to be Earth's dominant species within a year. The search area is widened, though the reason for the operation is kept top secret to avoid mass panic. Graham and Pat travel to
Brownsville, Texas, to interrogate a ranch foreman committed to a mental hospital after claiming he was forced down in his plane by
UFOs shaped like giant ants. One ant queen is discovered to have boarded a freighter in
Acapulco, Mexico, when, out in the Pacific Ocean, its offspring emerge and attack the crew. The
United States Navy cruiser that responds to the distress call finds only two surviving sailors in the water, and the freighter is sunk by naval gunfire. A report about a shipment of stolen sugar leads the investigators to a Los Angeles hospital, where a chronic
alcoholic claims he has seen giant ants in the city's storm drain system. When they also trace the movements of a man whose mutilated body was found in the area back to the drains and discover another giant ant print, they are convinced that both the final missing queen and the man's two missing young sons are somewhere in the over 700 miles of tunnels under the city. Martial law is declared in Los Angeles, and a curfew imposed. Peterson, Graham, and the Medfords help the armed forces search the drain network, and Peterson finds the boys trapped by some ants. He calls for reinforcements and is just able to lift the boys to safety before being attacked and killed. Graham arrives with backup, and the queen and her hatchlings are located. The Medfords confirm that no new queens have gotten away and sanction the destruction of the nest. Graham wonders what havoc might ensue from all of the other nuclear explosions in the past decade, and Harold responds that mankind has entered a new world, and no one can predict what we will find. ==Cast==