You scratch my back… the beneficial (and not so beneficial) relationships between organisms

To call someone a “parasite” is an insult. But the word has rather a different meaning in biology. Etymologically speaking, the earliest known record of the word parasite in the English language was in 1539, when it was defined as “a hanger-on, a toady, a person who lives on others”. The word itself was derived from the Greek parasitos, meaning “a person who eats at the table of another”. The social use appears to precede the scientific use, which was first recorded in 1646 as “an animal or plant that lives on others”. Parasite might trigger distant memories of school lessons about fleas and tapeworms. But is this view accurate? As with most things in life, the answer is not as straightforward as it first appears.