The word “parasite” does not evoke good feelings: among humans, to be a parasite means to live off the backs of others, receiving without giving anything in return. In the scientific world, parasites have been first ignored and then viewed with some suspicion: in Darwin’s time, their presence and apparent “simplicity” also challenged the image of evolution, often understood as progress toward ever more complex and, in fact, superior forms.
That of parasites is a fascinating story, studded with courageous scientists who did not hesitate to immolate their bodies in order to collect data on these life forms, the most numerous on our planet. And it was worth it, because parasites play a vital role on our planet, influencing the ecosystem and the development of their hosts. Today we have a somewhat clearer view of the ecological role and importance of parasites, as well as their evolution. It is a vision that restores justice to these little creatures that have been neglected for too long, and testifies to how complex the web of interactions among organisms in an ecosystem can be.
In addition, the study of parasites can provide us with valuable information on species interactions, and offer a window into the past and models for making future predictions to meet the environmental challenges that lie ahead.
Between history and science, science popularizer Willy Guasti guides us to the discovery of this strange and wonderful army of unwanted guests, which perhaps we should reevaluate.

Willy Guasti is a science popularizer: he has been the face of Focus TV and runs the YouTube channel Zoosparkle, one of the most followed projects dedicated to animals, evolution and paleontology in Italy. He has published Il coccodrillo ha un cuore tenero (Rizzoli 2022) and Dinosauri eccellenti (Gribaudo 2024).