We think of them with revulsion, but a new book wants us to appreciate their redeeming qualities.

Even when the victims aren’t people, there is something about parasites that arouses appalled fascination. The authors of “Parasite” mention the monster in the film “Alien” as a kind of archetype of the gross-outs in which the field abounds. There’s Cymothoa exigua, a louse that destroys fishes’ tongues and then lives in their mouths, performing a tongue’s functions while gorging itself. The fungus Ophiocordyceps unilateralis, which propagates itself by taking over ants’ bodies, has sufficient notoriety that it appears in the video game The Last of Us, where it zombifies people rather than ants.

By and large, Gardner, Diamond, and Racz resist filling their book with nightmarish creatures. As researchers at the University of Nebraska and its affiliated state museum, which has a large parasitological collection, they want to give us a new understanding of parasites, to counter our unalloyed horror and instill a more scientifically nuanced view. They do this by widening our focus, encouraging us to think in terms of ecosystems and evolutionary history. They write about how parasites may keep populations of species in balance, the ways in which they are imperilled by climate change, and what we owe them in terms of our understanding of genetics, organism development, and ancient human migrations.