Which is a foreign invader to the body that lives in or on a host and gets some or all of its nourishment from the host?

A foreign invader to the body that lives in or on a host and derives some or all of its nourishment from the host is called a parasite. Parasites can be organisms such as worms, protozoa, or ectoparasites like fleas and ticks. They often cause harm to the host by consuming nutrients or causing disease. This relationship typically benefits the parasite at the expense of the host.