What do you call animals which live on the surfaces of other animals?

Animals that live on the surfaces of other animals are called ectoparasites.

Here's a breakdown of the term:

* Ecto-: This prefix means "outside" or "external".

* Parasite: An organism that lives in or on another organism (the host) and benefits by deriving nutrients at the host's expense.

Some common examples of ectoparasites include:

* Fleas

* Ticks

* Lice

* Mites

* Some types of worms

It's important to distinguish ectoparasites from endoparasites, which live *inside* the body of their host (like tapeworms or roundworms).