William Tenn issued part of this novel originally in Galaxy Reader magazine under the title “The Men in the Walls” (1963). Of Men and Monsters proved to be a moderate success and helped him earn his place as an important science-fiction author.
The point this book emphasizes most strongly is the size and intelligence ratio of humans over other creatures, especially the cockroach. The tables have turned, and humans have been relegated to the status of vermin by the huge Monsters that have taken over Earth. The Monsters are so incredibly large, intelligent, and impervious to any human weapons that humans must live as pests, much like modern-day cockroaches. People inhabit the insides of Monster dwelling walls; rush out periodically to obtain food, trying not to be killed; and fight one another for territory, women, and belief systems.
The people battle the Monsters much the same way that cockroaches battle humans. More important, it is implied that humans deserve the Monster takeover because of the cruel treatment humans have imposed on other Earth creatures since the beginning of civilization. Domesticating the horse and cow, overbreeding animals to the point of gross physical deformities, and other acts of power over weaker creatures are finally balanced by the fact that humans are forced to live like animals. There are no other animals in the book.
Several Christian references are evident. An attack analogous to that of David against Goliath saves Eric in his first near-death ordeal, and the Aaron, head of the Aaron people, resembles popular images of God.
The great epiphany comes from the Aaron as he relates to Eric that humans are a superior sort of vermin and that they can survive best in “swarms” as parasites. At this statement, the reader and the protagonist realize how horrible humans truly are and that the only thing to do is to contrive to inhabit all the accessible universe.