The difference between commensalism and parasitism are:
Commensalism
- In this association, one organism is benefited while the other remains unaffected.
Image Source: bluecrabfarms.com/jmdpictures/bb.jpg
- There is no involvement of food. E.g. woodpeckers peck holes for nesting in tree trunks. After they abandon these holes, blue birds, use them for nesting.
Parasitism
- In this association, an organism lives in / on the body of another organism and derives benefit from it.
- Nutrition is obtained by the parasite at the expense of the host. E.g. ticks in dogs.