Parasitism describes a symbiotic relationship where one organism, the parasite, benefits while harming the other, the host. Common human parasites include ticks, tapeworms, and roundworms. Cuckoos are avian brood parasites that lay their eggs in the nests of other bird species like reed warblers. The cuckoo chick then evicts the host's eggs and chicks from the nest to monopolize all food from the host parents.