Wikipedia: New Mexico State Police troopers Ben Peterson (James Whitmore) and Ed Blackburn (Chris Drake) discover a little girl in shock, wandering the desert near Alamogordo, New Mexico. They retrace her steps to a mobile home owned by an FBI agent named Ellinson, who was on vacation in the area with his family. The side of the trailer was ripped open from the outside, the rest of the family is missing and no money was taken. A single unidentifiable animal track seems to be the only clue. Then a strange, pulsating high-pitched noise echos out of the desert on the wind. The little girl briefly reacts in fear when she hears the sound, but this is not noticed by those around her.
A general store owner named "Gramps" Johnson is found dead; his store is also torn apart from the outside. No cash was taken, but a barrel of sugar was smashed open. Gramps' Winchester rifle was fired and is now twisted out of shape. Peterson leaves by car to check on the little girl and make a report, leaving Blackburn to guard the store. Blackburn hears the strange, pulsating sound outside and leaves to investigate; off-camera gunshots are fired, the strange sound grows faster and louder, and Blackburn's scream is heard.
A plaster cast of the odd footprint found near the trailer is sent to Washington, D.C. Peterson's boss later points out that Gramps had time to fire all his ammunition at his attacker, and Peterson's missing partner was a "crack shot", eliminating the possibility of a homicidal maniac. Even more puzzling is the coroner's determination of Johnson's cause of death: a broken neck and back, skull fracture, crushed abdomen, and "enough formic acid in his body to kill 20 men".
The FBI sends Agent Robert Graham (James Arness) to investigate after the Bureau is unable to identify the footprint. With him he brings Drs. Harold Medford (Edmund Gwenn) and his daughter Pat Medford (Joan Weldon), both myrmecologists from the Department of Agriculture. The elder Medford examines the footprint. He later exposes the Ellinson girl to formic acid fumes, which revives her from a catatonic state; she screams, "Them! Them!"
Though his suspicions are validated by the girl's reaction, Medford will not reveal his theory; doing so prematurely might lead "to a nationwide panic". While investigating the Ellinson campsite, Pat screams when she encounters a giant, eight-foot long foraging ant. The lawmen run to her aid and empty their pistols into the insect with little effect. On directions from the elder Medford, Peterson and Graham destroy the ant's antennae, blinding it; they then kill it with sustained fire from a Thompson submachine gun. Harold finally reveals his theory: a colony of giant ants, mutated by radiation from the first atomic bomb test near Alamogordo, is responsible for the killings.
A helicopter search conducted by the Medfords, Peterson, Graham, and Major Kibby, on orders from General O'Brien, discovers the ants' nest. Cyanide gas bombs are tossed into it, and Graham, Peterson, and Pat descend into the nest to kill any survivors. Deep inside, Pat finds evidence that two queen ants have hatched and have escaped to establish new colonies. To avoid a general panic, the elder Medford gives a government task force a briefing on ants, as the government covertly investigates all reports of any unusual activity, even sightings of "flying saucers".
The first report comes from south Texas where a private pilot (Fess Parker) has been committed to a mental hospital after claiming that his aircraft was forced down by UFOs, shaped like giant ants. Next, the Coast Guard receives a report of a giant queen hatching her brood in the hold of a freighter at sea in the Pacific; giant ants attack the ship's crew and there are few survivors. The freighter is later sunk by U. S. Navy gunfire, eliminating one of the queens.
A third report comes in that leads Peterson, Graham, and Major Kibby to a rail yard in Los Angeles where a smashed boxcar has been emptied of 40 tons of sugar. An alcoholic in a hospital "drunk tank" claims to have seen giant ants outside his window. The mutilated body of a father is recovered, but his two young sons with him are missing. Peterson, Graham, and Kibby find evidence that the dad and kids were flying a model aircraft in the Los Angeles River drainage channel near the hospital. Given the apparent convergence of sightings, the President of the United States declares martial law in Los Angeles; more troops are assigned to find the new nest in the vast storm drain network under the city.
Peterson finds the two missing boys alive deep inside the drain system, but they are trapped near the ants' nest. He calls for reinforcements and goes in alone to rescue them, getting both boys to safety just before he is attacked by a giant ant. Graham arrives with reinforcements and kills the ant attacking Peterson, as others swarm to protect the nest. Peterson dies from his injuries. Graham and the other soldiers fight off the ants, but a tunnel collapse isolates Graham. Several ants charge him, but he is able to hold them off with his machine gun just long enough for the other troops to break through and make the rescue. The queen and her young hatchlings are discovered and destroyed with flame throwers.
Afterward, Dr. Medford makes a philosophic observation: "When Man entered the Atomic Age, he opened the door to a new world. What we may eventually find in that new world, nobody can predict."
Them featured in the "Insect Film Festival" in 2013, which was originated by Professor May Berenbaum, head of the Department of Entomology at the University of Illinois at Urbana-Champaign. It seems the good professor hadn't spotted Mr. Nimoy in Them yet when interviewed by National Geographic, because only his appearance in The Brain Eaters is mentioned. But then his scene is so brief that you might miss him if you blinked.
Insect Fear Film Festival: Just Like Cannes, Only With Spiders and Scorpions Instead of Jennifer Lawrence and Brad Pitt
I imagine most insect films meet the criteria of non-excellence. Is there anything above a grade B film in the genre?
The granddaddy of them all is Them! A 1954 film about an encounter with a race of giant ants. It was nominated for an Oscar and was Warner Brothers’ biggest grossing film that year. Angels and Insects (1995) won an Academy Award for costumes. Many big actors got their start in bug films. Clint Eastwood appeared as the jet pilot in Tarantula (1955). Leonard Nimoy appears in Braineaters (1958).
Are there trends in insect films?
In the 1950s big bug films were popular—oversized insects made so by radiation. What causes the mutation differs with the era. Genetically engineered big bugs came in the 1990s. In the 1970s, swarms were popular.
Source: National Geographic
Life Before Spock: The Early Sci-Fi Roles of Leonard Nimoy – By Philip Smolen
(...) Even the supporting actors are excellent. Leonard Nimoy has only one scene, but it’s very memorable. He plays an army sergeant who is collating strange phenomena reports for Dr. Medford. He tries to make time with a pretty female soldier and waxes poetic about people from Texas. It’s a great part and Nimoy plays it perfectly. Even though his role was small, Nimoy’s acting helped propel “Them” into a classic GMM [Giant Monster Movie] movie.
Leonard Nimoy, US Army Reserves (1953-1955)
In 1953, Leonard Nimoy served as a member of the United States Army Reserves. He received his final discharge in November 1955 with the rank of Sergeant. According to the National Archives, Nimoy's Army personnel file was destroyed in 1973 during a major fire at the National Personnel Records Center in St. Louis, Missouri... and as a result, there's not much public information about his service.
During the time of his enlistment, Nimoy appeared uncredited in, Them, Gordon Douglas' 1954 thriller about giant mutant ants birthed from radiation resulting from atomic testing. He played the role of a Air Force Sergeant, which was his real-life ranking at the time (albeit in the army)... perhaps as an extra in this film - he got the gig because he owned his own passable wardrobe?