From "Monster Movies: They Came from Beneath the Fifties" by Brian Murphy in Movies as Artifacts: Cultural Criticism of Popular Film, edited by Michael T. Marsden (New York: Rowman and Littlefield, 1982):

In 1954 (just about the height of the fashion for monster movies) appeared Them. It has all the ingredients. The setting is contemporary America, an America which is marvelously "ordinary," "normal," "nice." It is an America in which teenagers might do crazy things like drive funny cars too fast or neck on deserted roads—but, of course, they didn't wear beads and flowers or bomb post offices. The tranquility of this scene is broken by an isolated disaster—some strange doings someplace: maybe a lone night watchman is found murdered in such a way as to suggest death by most unnatural causes; and maybe his body has been contaminated by radium. At any rate, one of the sheriff's deputies or one of the bored local cops thinks that maybe they ought to call a "prof" at a nearby research station. There is an investigation. More killings. Reports—often by frightened teenagers lately necking (an obsessively recurring motif). Then a whole town realizes the danger, and there is, for a moment, panic and an absolutely uncontrollable fear.

So in Them, as in all monster movies, we turn to scientists and soldiers. They blur together, in fact: was it James Arness or James Whitmore who was the scientist? Well, there was a girl (Joan Weldon)—the busty assistant scientist (quite de rigueur), and in Them, we were allowed to see a great deal of her because she had "scientific knowledge" in "insect pathology." Presiding over all was the wise, elderly, unthreatening, and reassuring Edmund Gwenn. The scene in which he gives a scholarly discussion about the habits of ants was marvelously effective. The monsters, everyone knew, were giant ants; and, in order to deal with the obvious havoc they could wreak, we listen to a fatherly scientist begin at the beginning and, well within the clearly defined boundaries of science, tell us what we need to know.

Enlightened, James Arness and James Whitmore (and the busty specialist in insect pathology) go to do battle with Them (note the impersonal, paranoid, accusative form of the pronoun with no mentionable antecedent). The battle is a huge one—and yet curiously parochial: it involves all of America but only America. On one side are Them, those giant ants. Where did they come from? Scientist Gwenn explains that they are "mutations" which were the result of the first atom bomb explosion in 1945. Moreover, these mutations will proliferate in the way ordinary ants will, so the result will be, of course, catastrophic. There is only one fit adversary, and that cannot be some solitary Frankenstein's assistant or brilliant writer, some mere individual: no, the only fit adversary for such an enemy is the Government of the United States of America. So, Arness and Whitmore are backed up by all resources of the Government, scientific and military, operated by an inevitable "open line to Washington."

One consequence of such battle lines is that the country is absolutely unified. In the face of such an enemy as Them, Americans respond nobly: they do precisely as they are told. The ants are discovered nesting in the sewer system of Los Angeles. Whitmore and Arness and the busty pathologist get to work. But what about the panic-stricken citizens? An announcer goes on the radio and the television air waves to utter a sentence which echoes through all the monster movies and which, indeed, echoes through all the fifties: "Your personal safety depends upon your cooperation with the military authorities."

As a film, Them succeeds admirably in making such a sentence thoroughly convincing. The triumph in the film is, of course, the destruction of Them: it is a triumph of science and the military and the country itself. The film makes the triumph powerful enough by showing the pathos of private agonies. The climax of the film involves the search for the ants in the Los Angeles sewer system. But there are children playing in there someplace, and in order to save the children, in a brilliantly done scene with stunning technical effects (those bloody ants are frightening), James Whitmore has to die horribly. Well, that is the cost: the individual perishes so that the country as a whole (convincingly symbolized for the moment in the children trapped by Them) might survive and return to what it wants so desperately—a nice, safe world in which teenagers drive hot rods and neck a lot. The last lines of Them are spoken by Edmund Gwenn as he muses on this "atomic age," this—the very last words of the film—"new world."

It is not a very brave new world, and it is a new world which no one wants. But it is a new world which we, in actual, appalling fact, have; and there is no getting out of it. Those beasts and things—Them generally—are awfully real; and, it seemed, we could deal with them only by going back to the very real people who spawned them: the scientists working "in full cooperation" (such an important word, that "cooperation") with the military.