Here's why:

* Dependence: Parasites rely entirely on their host for survival. They need the host for food, shelter, and sometimes even reproduction.

* Harm: The parasite causes harm to its host, often through disease, weakening, or stealing nutrients.

Examples of parasites include:

* Tapeworms: Live in the intestines of animals and humans, absorbing nutrients from their host.

* Fleas: Feed on the blood of mammals, causing itching and discomfort.

* Malaria parasites: Live in mosquitoes and humans, causing a potentially deadly disease.

Let me know if you'd like to explore any of these examples in more detail!